guanosine-diphosphate and mastoparan

Recombinant heterotrimeric G-protein α(i1), α(i2) and α(i3) subunits were purified in GDP-depleting conditions by affinity chromatography using StrepII-tagged β₁γ₂ subunits. Real-time monitoring of fluorescence anisotropy of Bodipy-FL-GTPγS was used for characterization of nucleotide binding properties and inactivation of the purified proteins. All GDP-depleted α(i) were unstable at room temperature and therefore nucleotide binding could be characterized only in a nonequilibrium state. In comparison to Mg²⁺, Mn²⁺ inhibited nucleotide binding to all α(i)-heterotrimers studied and accelerated nucleotide release. Mn²⁺ had stabilizing effect on the nucleotide free state of the α(i1) subunit, whereas both Mn²⁺ as well as G-protein activation by mastoparan destabilized the α(i2) subunit.

Topics: Animals; Cell Line; Fluorescence Polarization; GTP-Binding Protein alpha Subunits, Gi-Go; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; Guanosine Triphosphate; Humans; Intercellular Signaling Peptides and Proteins; Magnesium; Manganese; Peptides; Protein Multimerization; Protein Stability; Protein Structure, Quaternary; Protein Subunits; Wasp Venoms

Application of the tetradecapeptide mastoparan to the prothoracic glands (PGs) of the tobacco hornworm, Manduca sexta, and the silkworm, Bombyx mori, resulted in increases in intracellular Ca(2+) ([Ca(2+)](i)). In M. sexta, Gi proteins are involved in the mastoparan-stimulated increase in [Ca(2+)](i). However, there is no involvement of Gi proteins in the mastoparan-stimulated increase in [Ca(2+)](i) in prothoracic gland cells from B. mori. Unlike in M. sexta prothoracic glands, in B. mori prothoracic glands mastoparan increases [Ca(2+)](i) even in the absence of extracellular Ca(2+). Pharmacological manipulation of the Ca(2+) signalling cascades in the prothoracic glands of both insect species suggests that in M. sexta prothoracic glands, mastoparan's first site of action is influx of Ca(2+) through plasma membrane Ca(2+) channels while in B. mori prothoracic glands, mastoparan's first site of action is mobilization of Ca(2+) from intracellular stores. In M. sexta, the combined results indicate the presence of mastoparan-sensitive plasma membrane Ca(2+) channels, distinct from those activated by prothoracicotropic hormone or the IP(3) signalling cascade, that coordinate spatial increases in [Ca(2+)](i) in prothoracic gland cells. We propose that in B. mori, mastoparan stimulates Ca(2+) mobilization from ryanodine-sensitive intracellular Ca(2+) stores in prothoracic gland cells.

Topics: Animals; Bombyx; Boron Compounds; Calcium; Calcium Signaling; Dose-Response Relationship, Drug; Gadolinium; Guanosine Diphosphate; Intercellular Signaling Peptides and Proteins; Manduca; Peptides; Pertussis Toxin; Ryanodine; Thapsigargin; Thionucleotides; Time Factors; Wasp Venoms

In addition to a bicarbonate-regulated soluble adenylyl cyclase (sAC), mammalian spermatozoa, like somatic cells, appear to contain receptor/G protein-regulated AC activity that contributes to the modulation of specialized cell processes. This study provides evidence that agents, known to influence somatic membrane-associated AC (mAC) but apparently not germ cell sAC, can modulate cAMP production and functional state in mouse spermatozoa. Specifically, forskolin significantly enhanced cAMP production and capacitation, while inclusion of 2',5'-dideoxyadenosine significantly blocked these responses. Furthermore, GTPgammaS and NaF stimulated cAMP, but GDPbetaS and mastoparan had no apparent effect, consistent with recent evidence that G(s), but not G(i), contributes to AC/cAMP regulation in uncapacitated cells. In addition, intact mouse spermatozoa were screened for all known mAC isoforms by immunolocalization, using commercially available specific antibodies. The most abundant isoforms appeared to be AC2, AC3, and AC8, each with distinct distributions in the acrosomal and flagellar regions; AC1 and AC4 also appeared to be present, although less abundantly, in the midpiece and acrosomal cap regions, respectively. Intriguingly, however, Western blotting revealed that the major immunoreactive proteins in mouse sperm lysates were considerably smaller (approximately 50-60 kDa) than their somatic cell counterparts, suggesting that mature spermatozoa contain multiple mACs which may function in a shortened form. Of particular interest were AC3 and AC8, located in the same regions as, and hence possibly directly associated with, specific cell surface receptors and G proteins that are able to regulate the spermatozoon's acquisition and maintenance of fertilizing ability via changes in AC/cAMP.

Topics: Adenylyl Cyclases; Animals; Colforsin; Cyclic AMP; Dideoxyadenosine; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; Intercellular Signaling Peptides and Proteins; Isoenzymes; Male; Mice; Peptides; Receptors, Cell Surface; Signal Transduction; Sodium Fluoride; Sperm Capacitation; Spermatozoa; Thionucleotides; Wasp Venoms

Mastoparan, a hormone receptor-mimetic peptide isolated from wasp venom, stimulates insulin release from pancreatic beta-cells in a Ca(2+)-independent but GTP-dependent manner. In this report, the role of the Rho family GTP-binding protein Cdc42, in the mastoparan stimulus-secretion pathway, was examined. Overexpression of wild-type Cdc42 in beta HC-9 cells, an insulin-secreting mouse-derived cell line, resulted in a 2-fold increase in mastoparan-stimulated insulin release over vector-transfected beta HC-9 cells. This effect was not seen with secretagogues such as glucose that stimulate secretion via Ca(2+)-dependent pathways. GDP/GTP exchange assay data and studies with pertussis (PTX) toxin suggest that mastoparan may work directly to activate Cdc42 and not via PTX-sensitive heterotrimeric GTP-binding proteins. Using bacterial glutathione S-transferase-Cdc42 fusion proteins and co-immunoprecipitation and transient transfection studies, Cdc42 was shown to be an upstream regulator of the exocytotic protein, syntaxin. These results suggest that the GTP-dependent signal underlying the mastoparan effect acts at a "distal site" in stimulus-secretion coupling on one of the SNARE proteins essential for exocytosis. In vitro binding assays, using purified Cdc42 and syntaxin proteins, show that Cdc42 mediates the GTP signal through an indirect association with syntaxin. The H3 domain at the C-terminus of syntaxin, which participates in the formation of the ternary SNARE complex with the core proteins, SNAP-25 and synaptobrevin, is also required for the association with Cdc42. Thus, these studies indicate that Cdc42 could be a putative GTP-binding protein thought to be involved in the mastoparan-stimulated GTP-dependent pathway of insulin release.

Topics: Animals; cdc42 GTP-Binding Protein; Cell Line; Guanosine Diphosphate; Guanosine Triphosphate; Insulin; Insulin Secretion; Intercellular Signaling Peptides and Proteins; Membrane Proteins; Mice; Peptides; Qa-SNARE Proteins; Wasp Venoms

The hyperpolarizing receptor potential of scallop ciliary photoreceptors is attributable to light-induced opening of K(+)-selective channels. Having previously demonstrated the activation of this K(+) current by cGMP, we examined upstream events in the transduction cascade. GTP-gamma-S produced persistent excitation after a flash, accompanied by decreased sensitivity and acceleration of the photocurrent, whereas GDP-beta-S only inhibited responsiveness, consistent with the involvement of a G-protein. Because G(o) (but not G(t) nor G(q)) recently has been detected in the ciliary retinal layer of a related species, we tested the effects of activators of G(o); mastoparan peptides induced an outward current suppressible by blockers of the light-sensitive conductance such as l-cis-diltiazem. In addition, intracellular dialysis with the A-protomer of pertussis toxin (PTX) depressed the photocurrent. The mechanisms that couple G-protein stimulation to changes in cGMP were investigated. Intracellular IBMX enhanced the photoresponse with little effect on the baseline current, a result that argues against regulation by light of phosphodiesterase activity. LY83583, an inhibitor of guanylate cyclase (GC), exerted a reversible, dose-dependent suppression of the photocurrent. By contrast, ODQ, an antagonist of NO-sensitive GC, and YC-1, an activator of NO-sensitive GC, failed to alter the light response or the holding current; furthermore, the NO synthase inhibitor N-methyl- l-arginine was inert, indicating that the NO signaling pathway is not implicated. Taken together, these results suggest a novel type of phototransduction cascade in which stimulation of a PTX-sensitive G(o) may activate a membrane GC to induce an increase in cGMP and the consequent opening of light-dependent channels.

Topics: Animals; Calcium Channel Blockers; Dose-Response Relationship, Drug; Enzyme Inhibitors; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; Guanylate Cyclase; In Vitro Techniques; Intercellular Signaling Peptides and Proteins; Mollusca; Nitric Oxide Synthase; Patch-Clamp Techniques; Peptides; Pertussis Toxin; Phosphodiesterase Inhibitors; Photic Stimulation; Photoreceptor Cells, Invertebrate; Retina; Signal Transduction; Thionucleotides; Virulence Factors, Bordetella; Wasp Venoms

Known nucleoside diphosphate kinases (NDPKs) are oligomers of 17-23-kDa subunits and catalyze the reaction N1TP + N2DP --> N1DP + N2TP via formation of a histidine-phosphorylated enzyme intermediate. NDPKs are involved in the activation of heterotrimeric GTP-binding proteins (G-proteins) by catalyzing the formation of GTP from GDP, but the properties of G-protein-associated NDPKs are still incompletely known. The aim of our present study was to characterize NDPK in soluble preparations of the retinal G-protein transducin. The NDPK is operationally referred to as transducin-NDPK. Like known NDPKs, transducin-NDPK utilizes NTPs and phosphorothioate analogs of NTPs as substrates. GDP was a more effective phosphoryl group acceptor at transducin-NDPK than ADP and CDP, and guanosine 5'-[gamma-thio]triphosphate (GTP[S]) was a more effective thiophosphoryl group donor than adenosine 5'-[gamma-thio]triphosphate (ATP[S]). In contrast with their action on known NDPKs, mastoparan and mastoparan 7 had no stimulatory effect on transducin-NDPK. Guanosine 5'-[beta, gamma-imido]triphosphate (p[NH]ppG) potentiated [3H]GTP[S] formation from [3H]GDP and ATP[S] but not [3H]GTP[S] formation from [3H]GDP and GTP[S]. Depending on the thiophosphoryl group acceptor and donor, [3H]NTP[S] formation was differentially regulated by Mg2+, Mn2+, Co2+, Ca2+ and Zn2+. [gamma-32P]ATP and [gamma-32P]GTP [32P]phosphorylated, and [35S]ATP[S] [35S]thiophosphorylated, a 36-kDa protein comigrating with transducin-beta. p[NH]ppG potentiated [35S]thiophosphorylation of the 36-kDa protein. 32P-labeling of the 36-kDa protein showed characteristics of histidine phosphorylation. There was no evidence for (thio)phosphorylation of 17-23-kDa proteins. Our data show the following: (a) soluble transducin preparations contain a GDP-prefering and guanine nucleotide-regulated NDPK; (b) transducin-beta may serve as a (thio)phosphorylated NDPK intermediate; (c) transducin-NDPK is distinct from known NDPKs and may consist of multiple kinases or a single kinase with multiple regulatory domains.

Topics: Animals; Cations, Divalent; Cattle; Edetic Acid; Guanosine Diphosphate; In Vitro Techniques; Intercellular Signaling Peptides and Proteins; Kinetics; Nucleoside-Diphosphate Kinase; Peptides; Phosphorylation; Protein Conformation; Rod Cell Outer Segment; Solubility; Transducin; Wasp Venoms

The whole-cell patch-clamp membrane capacitance measurement was used to monitor secretory activity in rat melanotrophs, while rab3AL, putative effector domain peptides of Rab3 small GTPases (20-30 kDa), were introduced into cytosol. In melanotrophs dialyzed with calcium free solutions membrane capacitance tends to decrease slightly. This decrease is further potentiated with GDPbetaS (500 microM). We found that rab3AL (100 microM) stimulated secretory activity in the absence of calcium. The rab3AL response was qualitatively comparable to the response to mastoparan (1 microM), an activator of certain heterotrimeric GTP-binding proteins. Interestingly, inclusion of GDPbetaS (500 microM) resulted in a blockade of both rab3AL and mastoparan induced responses. We conclude that rab3AL and mastoparan induce calcium-independent stimulation of secretory activity in rat melanotrophs by activation of a downstream heterotrimeric GTP-binding protein.

Topics: Amino Acid Sequence; Animals; Calcium; Cells, Cultured; Drug Synergism; Electrophysiology; GTP-Binding Proteins; Guanosine Diphosphate; Intercellular Signaling Peptides and Proteins; Molecular Sequence Data; Patch-Clamp Techniques; Peptides; Pituitary Gland; Rats; Thionucleotides; Wasp Venoms

We have examined the effects of the tachykinin substance P on the action potential of lamprey mechanosensory dorsal cells. Substance P increased the spike duration and reduced the afterhyperpolarization. These effects were mimicked by stimulation of the dorsal root, which contains tachykinin-like immunoreactive fibres. The tachykinin antagonist spantide II blocked the effects of both substance P and dorsal root stimulation. The spike broadening was voltage-dependent, and was due to the reduction of a 4-aminopyridine-sensitive potassium conductance. The spike broadening was mimicked by G-protein activators and blocked by the G-protein inhibitor GDPbetaS. Pertussis toxin did not block the effects of substance P. The spike broadening was blocked by the protein kinase C and cAMP-dependent protein kinase inhibitor H7, and by the specific protein kinase C antagonist chelerythrine, but not by the cAMP and cGMP-dependent protein kinase inhibitor H8. The phorbol ester phorbol 12,13-dibutyrate mimicked and blocked the effects of substance P, supporting the role of protein kinase C in the spike modulation. The adenylate cyclase activator forskolin and the cAMP agonist SpcAMPs mimicked but did not block the effects of substance P on the spike duration, suggesting that protein kinase A also modulates the dorsal cell action potential, but that substance P acts independently of this pathway. Substance P also increased the excitability of the dorsal cells. This effect was blocked by 4-AP, PDBu and chelerythrine, but not by H8, suggesting that the increase in excitability shares the same intracellular and effector pathways as the spike broadening.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; 4-Aminopyridine; Action Potentials; Adenylate Cyclase Toxin; Alkaloids; Animals; Benzophenanthridines; Cadmium Chloride; Electric Stimulation; Enzyme Inhibitors; Female; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; In Vitro Techniques; Intercellular Signaling Peptides and Proteins; Lampreys; Male; Neurons; Notochord; Peptides; Pertussis Toxin; Phenanthridines; Phorbol 12,13-Dibutyrate; Potassium Channels; Protein Kinase C; Protein Kinases; Spinal Cord; Substance P; Tetraethylammonium; Thionucleotides; Virulence Factors, Bordetella; Wasp Venoms

Topics: Amino Acid Sequence; Animals; Cations; Detergents; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; Guanosine Triphosphate; Intercellular Signaling Peptides and Proteins; Kinetics; Lipids; Macromolecular Substances; Mast Cells; Molecular Sequence Data; Peptides; Phosphorus Radioisotopes; Radioisotope Dilution Technique; Tritium; Wasp Venoms

Studies have shown that mastoparan and other amphiphilic peptides induce exocytosis of hormones from anterior pituitary cells. We have studied the effect of mastoparan on the secretion of prolactin from cultured rat anterior pituitary cells and on the concomitant functional status of signal-transducing pathways in lactotroph-enriched cell cultures. Mastoparan stimulation of prolactin secretion was dose-dependent, time-dependent, reversible and required the presence of calcium. Pretreatment of pituitary cell cultures with cholera and pertussis toxin had no effect on the secretory response, whereas encapsulation of guanosine 5-[beta-thio]diphosphate (GDP-beta-S) by reversible electropermeabilization inhibited mastoparan-stimulated secretion. Incubation of mastoparan with myo-[3H]inositol-labelled lactotroph-enriched anterior pituitary cell cultures resulted in increased formation of inositol phosphates compared with control cells, and encapsulation of GDP-beta-S blocked mastoparan-induced inositol lipid hydrolysis. Mastoparan caused translocation of protein kinase C activity from a soluble to a membrane-attached form. Mastoparan was able to increase the intracellular Ca2+ concentration in Fura-2-loaded individual lactotrophs. Omission of Ca2+ from the extracellular medium did not change the Ca2+ response in lactotrophs when stimulated with mastoparan. On the basis of these results it is concluded that mastoparan-induced release of prolactin is preceded by activation of the inositol(1,4,5)trisphosphate/diacylglycerol pathway with resulting translocation of protein kinase activity and increment in intracellular Ca2+. However, other signal-transducing pathways may be involved in the secretory process.

Topics: Animals; Calcium; Cells, Cultured; Cholera Toxin; Dose-Response Relationship, Drug; Guanosine Diphosphate; Inositol Phosphates; Intercellular Signaling Peptides and Proteins; Kinetics; Peptides; Pertussis Toxin; Pituitary Gland, Anterior; Prolactin; Protein Kinase C; Rats; Thionucleotides; Virulence Factors, Bordetella; Wasp Venoms

Mastoparan (MP) is a component of wasp venom which stimulates secretion from a number of cell types. We have used intact and electrically permeabilised islets of Langerhans to investigate the mechanisms through which MP stimulates insulin secretion from pancreatic beta-cells. MP caused a temperature-dependent and dose-related stimulation of insulin secretion from intact islets at a substimulatory concentration (2 mM) of glucose, which was not dependent upon the presence of extracellular Ca2+. MP also stimulated ATP-independent insulin secretion from electrically permeabilised islets in which intracellular Ca2+ was clamped at a substimulatory concentration (50 nM). MP-induced insulin secretion was not inhibited by down-regulation of islet protein kinase C, nor by the protein kinase inhibitor staurosporine, nor by the cyclic AMP antagonist Rp-adenosine 3',5'-cyclic phosphorothioate. However, MP-induced secretion from permeabilised islets was inhibited by the presence of guanosine 5'-O-2-thiodiphosphate. These results suggest that MP stimulates insulin secretion by a mechanism that is independent of changes in cytosolic Ca2+ or protein kinase activation, but which is dependent, at least in part, upon activation of a GTP-binding protein at a late stage in the secretory process.

Topics: Adenosine Triphosphate; Alkaloids; Amino Acid Sequence; Animals; Calcium; Cell Membrane Permeability; Cyclic AMP; Enzyme Activation; Glucose; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; Insulin; Insulin Secretion; Intercellular Signaling Peptides and Proteins; Islets of Langerhans; Molecular Sequence Data; Peptides; Phosphorylation; Protein Kinase C; Protein Kinase Inhibitors; Protein Processing, Post-Translational; Rats; Signal Transduction; Staurosporine; Stimulation, Chemical; Tetradecanoylphorbol Acetate; Thionucleotides; Wasp Venoms

We have examined the effects of various agonists and antagonists of GTP-binding proteins on receptor-mediated endocytosis in vitro. Stage-specific assays which distinguish coated pit assembly, invagination, and coat vesicle budding have been used to demonstrate requirements for GTP-binding protein(s) in each of these events. Coated pit invagination and coated vesicle budding are both stimulated by addition of GTP and inhibited by GDP beta S. Although coated pit invagination is resistant to GTP gamma S, A1F4-, and mastoparan, late events involved in coated vesicle budding are inhibited by these antagonists of G protein function. Earlier events involved in coated pit assembly are also inhibited by GTP gamma S, A1F4-, and mastoparan. These results demonstrate that multiple GTP-binding proteins, including heterotrimeric G proteins, participate at discrete stages in receptor-mediated endocytosis via clathrin-coated pits.

Topics: Aluminum; Aluminum Compounds; Amino Acid Sequence; Coated Pits, Cell-Membrane; Endocytosis; Fluorides; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; Guanosine Triphosphate; Humans; In Vitro Techniques; Intercellular Signaling Peptides and Proteins; Molecular Sequence Data; Peptides; Receptors, Transferrin; Thionucleotides; Tumor Cells, Cultured; Wasp Venoms

Recent studies have shown that mastoparan, an amphiphilic peptide derived from wasp venom, accelerates guanine nucleotide exchange and GTPase activity of purified GTP-binding proteins. In the present study we have examined the functional consequences of exposure of intact human platelets to mastoparan. Mastoparan promoted rapid (less than or equal to 1 min) dose-dependent increases in 5-hydroxy[14C]tryptamine and beta-thromboglobulin release from dense-granule and alpha-granule populations respectively. The exocytotic response did not result from a lytic effect of mastoparan and occurred in the complete absence of platelet shape change and aggregation. Liberation of [3H]arachidonate and increases in cytosolic [Ca2+] (detected with fura 2) were not observed in platelets stimulated with mastoparan. Similarly, in platelets preloaded with [3H]inositol during reversible electroporation, mastoparan did not cause the accumulation of [3H]inositol phosphates. Mastoparan-induced secretion was unaffected by preincubation with either the protein kinase C inhibitor staurosporine (10 nM-10 microM) or prostacyclin (PGI2; 100 ng/ml) and was not accompanied by phosphorylation of the 45 kDa protein kinase C substrate or the 20 kDa protein normally associated with platelet activation. The G-protein inhibitor guanosine 5'-[beta-thio]diphosphate (GDP[S]; 1 mM) attenuated the secretion induced by mastoparan in both intact and saponin-permeabilized platelets. Encapsulation of GDP[S] during reversible permeabilization inhibited mastoparan-induced secretion, providing evidence for an intracellular action of GDP[S]. In all these studies thrombin (0.05-0.2 unit/ml) elicited characteristic responses, and thrombin-induced secretion was inhibited by staurosporine, PGI2 and GDP[S]. Mastoparan also increased intra-platelet cyclic AMP in a dose-dependent manner. Mastoparan and PGI2 increased 32P incorporation into a protein of approx. 24 kDa, whereas phosphorylation of a 50 kDa substrate was only seen in PGI2-stimulated platelets. These results indicate that mastoparan promotes secretion by a mechanism which does not involve stimulation of phospholipase C and suggest that the secretory event may result either from a direct fusogenic action of mastoparan and/or from stimulation of the putative exocytosis-linked G-protein, Ge.

Topics: Alkaloids; Amino Acid Sequence; Arachidonic Acids; Blood Platelets; Calcium; Cyclic AMP; Cytoplasmic Granules; Dose-Response Relationship, Drug; Epoprostenol; Exocytosis; GTP-Binding Proteins; Guanosine Diphosphate; Humans; In Vitro Techniques; Intercellular Signaling Peptides and Proteins; Molecular Sequence Data; Peptides; Phosphatidylinositols; Platelet Activation; Saponins; Staurosporine; Thionucleotides; Thrombin; Wasp Venoms

Guanosine triphosphate (GTP)-binding proteins are required for intracellular vesicular transport. Mastoparan is a peptide component of wasp venom that increases nucleotide exchange in some classes of G alpha subunits of regulatory heterotrimeric GTP-binding proteins (G proteins). Mastoparan and other compounds that increase nucleotide exchange by G proteins inhibited endosome fusion in vitro and reversed the effects of guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S), a nonhydrolyzable GTP analog. Addition of beta gamma subunits of G proteins to the fusion assay antagonized the stimulatory effect of GTP-gamma-S, confirming the participation of G proteins. These results indicate that GTP-binding proteins are required for endosome fusion and in particular that a G protein is involved. Given the function of G proteins in signal transduction, these findings may provide insight into the mechanism by which endosomal vesicles become competent for fusion after their formation at the cell surface.

Topics: Biological Transport; Endocytosis; Endosomes; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; Guanosine Triphosphate; Intercellular Signaling Peptides and Proteins; Intracellular Membranes; Macromolecular Substances; Membrane Fusion; Organelles; Peptides; Wasp Venoms

Effects of guanine nucleotides on glucose transport were studied in permeabilized rat epididymal fat cells. GTP gamma S and Gpp(NH)p, but not App(NH)p, stimulated 3-O-methylglucose transport. Effect of GTP gamma S was dose-dependent, being detectable at 0.1 mM, and 1.0 mM GTP gamma S stimulated glucose transport to the same extent as insulin. GTP gamma S (0.3 mM) enhanced insulin-stimulated glucose transport while 1 mM GTP gamma S did not affect insulin-mediated transport. GDP beta S had no effect on glucose transport by itself but rather enhanced insulin action. NaF, which is known to activate trimeric G proteins, increased glucose transport to the same extent as insulin. Likewise, mastoparan augmented glucose transport. These results indicate that a certain type of trimeric G protein(s) is involved in the regulation of glucose transport.

Topics: 3-O-Methylglucose; Adenylyl Imidodiphosphate; Adipose Tissue; Animals; Biological Transport; Cell Membrane Permeability; Cells, Cultured; Dose-Response Relationship, Drug; Electric Stimulation; Glucose; Guanine Nucleotides; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; Guanylyl Imidodiphosphate; Insulin; Intercellular Signaling Peptides and Proteins; Male; Methylglucosides; Peptides; Rats; Rats, Sprague-Dawley; Sodium Fluoride; Thionucleotides; Wasp Venoms