beta-escin and aluminum-fluoride

Halothane directly relaxes airway smooth muscle partly by decreasing the Ca2+ sensitivity. In smooth muscle, receptor stimulation is thought to increase Ca2+ sensitivity via a cascade of heterotrimeric and small monomeric guanine nucleotide-binding proteins (G-proteins). Whether this model is applicable in the airway and where halothane acts in this pathway were investigated.. A beta-escin-permeabilized canine tracheal smooth muscle preparation was used. Exoenzyme C3 of Clostridium botulinum, which inactivates Rho monomeric G-proteins, was used to evaluate the involvement of this protein in the Ca2+ sensitization pathway. The effects of halothane on different stimulants acting at different levels of signal transduction were compared: acetylcholine on the muscarinic receptor, aluminum fluoride (AIF4-) on heterotrimeric G-proteins, and guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) on all G-proteins.. Exoenzyme C3 equally attenuated acetylcholine- and AIF4--induced Ca2+ sensitization, suggesting that these pathways are both mediated by Rho. Halothane applied before stimulation equally attenuated acetylcholine- and AIF4--induced Ca2+ sensitization. However, when added after Ca2+ sensitization was established, the effect of halothane was greater during Ca2+ sensitization induced by acetylcholine compared with AIF4-, which, along with the previous result, suggests that halothane may interfere with dissociation of heterotrimeric G-proteins. Halothane applied during GTPgammaS-induced Ca2+ sensitization had no significant effect on force, suggesting that halothane has no effect downstream from monomeric G-proteins.. Halothane inhibits increases in Ca2+ sensitivity of canine tracheal smooth muscle primarily by interfering with the activation of heterotrimeric G-proteins, probably by inhibiting their dissociation.

Topics: Acetylcholine; ADP Ribose Transferases; Aluminum Compounds; Anesthetics, Inhalation; Animals; Botulinum Toxins; Calcium; Dogs; Escin; Female; Fluorides; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Halothane; In Vitro Techniques; Isometric Contraction; Male; Muscle, Smooth; Trachea

We studied the involvement of protein kinase C (PKC) and a small GTP-binding protein (G-protein), rho, in receptor-mediated Ca2+ sensitization of the contractile apparatus of smooth muscle of guinea pig vas deferens. In beta-escin-permeabilized smooth muscle strips, norepinephrine (NE) in the presence of GTP caused further contraction of the preparations at a constant Ca2+ level (Ca2+ sensitization). Prazosin and GDP beta S, a nonhydrolyzable GDP analogue, inhibited NE-induced Ca2+ sensitization, indicating an alpha-1 adrenoceptor/G-protein mediated response. GTP alone (> 10 microM) and GTP gamma S, a non-hydrolyzable GTP analogue, also induced Ca2+ sensitization. Pretreatment of preparations with C3 exoenzyme of Clostridium botulinum, which is known to ADP-ribosylate rho family proteins, with NAD resulted in complete inhibition of NE- and GTP (GTP gamma S)-induced Ca2+ sensitization. AIF4-, which activates heterotrimeric G-, but not small G-protein also induced Ca2+ sensitization. Interestingly, AIF4(-)-induced Ca2+ sensitization was inhibited by not only GDP beta S but also C3-treatment, suggesting that activation of heterotrimeric GTP-binding protein precedes activation of rho protein. On the other hand, phorbol 12,13-dibutyrate, like NE, also induced Ca2+ sensitization. The sensitization was inhibited by PKC(19-31), a PKC inhibitor peptide. However, PKC(19-31) did not have any effect on NE- or AIF4(-)-induced Ca2+ sensitization.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adenosine Diphosphate Ribose; ADP Ribose Transferases; Aluminum Compounds; Animals; Botulinum Toxins; Calcium; Escin; Fluorides; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Triphosphate; Guinea Pigs; In Vitro Techniques; Male; Muscle Contraction; Muscle, Smooth; Norepinephrine; Peptides; Phorbol 12,13-Dibutyrate; Protein Kinase C; rho GTP-Binding Proteins; Vas Deferens