cyclic-gmp and proctolin

As in many other arthropods, the neuropeptide proctolin enhances contractures of muscles in the crustacean isopod Idotea emarginata. The enhancement of high K+-induced contractures by proctolin (1 micromol l-1) was mimicked upon application of the protein kinase C (PKC) activator phorbol-12-myristate 1-acetate (PMA) and was inhibited by the PKC inhibitor bisindolylmaleimide (BIM-1). The potentiation was not inhibited by H89, a protein kinase A (PKA) inhibitor. Proctolin did not change the intracellular concentration of 3',5'-cyclic adenosine monophosphate (cAMP) whereas it significantly reduced the intracellular concentration of 3',5'-cyclic guanosine monophosphate (cGMP). The reduction of cGMP was not observed in the presence of the PKC inhibitor BIM-1. 8-Bromo-cGMP, a membrane-permeable cGMP analogue, reduced the potentiating effect of proctolin on muscle contracture. We thus conclude that proctolin in the studied crustacean muscle fibres induces an activation of PKC, which leads to a reduction of the cGMP concentration and, consequently, to the potentiation of muscle contracture.

Topics: Animals; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Isopoda; Isoquinolines; Male; Muscle Contraction; Muscle, Skeletal; Neuropeptides; Oligopeptides; Potassium; Protein Kinase C; Protein Kinase Inhibitors; Sulfonamides

1. The catecholamines dopamine, epinephrine and norepinephrine were detected in alumina extracts of Limulus midgut tissue using high performance liquid chromatography with electrochemical detection. Moderate levels of norepinephrine (28.2 +/- 2.1 ng/g) and dopamine (24.0 +/- 5.2 ng/g) were detected in the midgut, while epinephrine levels (7.4 +/- 0.9 ng/g) were less. Catecholamines were present in all regions along the longitudinal axis of the midgut, and norepinephrine and dopamine levels were highest in posterior regions. 2. Catecholamines decreased muscle tonus and inhibited spontaneous contractions of the Limulus midgut. Dopamine typically decreased spontaneous midgut activity at doses of 10(-8) M or greater, and produced inhibitory actions on all regions of the Limulus midgut. In some preparations epinephrine and norepinephrine elicited a secondary rhythmicity. The actions of dopamine opposed the excitatory effects produced by either proctolin or octopamine. 3. Catecholamines significantly elevated levels of cyclic AMP in Limulus midgut muscle rings. Dopamine (10(-5) M) increased cyclic AMP with a time course consistent with its physiological effects. Forskolin and several methyl xanthines increased Limulus midgut cyclic AMP levels and mimicked the inhibitory effects of dopamine on the isolated midgut preparation. Cyclic nucleotide analogues also produced dopamine-like effects on the isolated midgut preparation. Inhibition of cyclic nucleotide phosphodiesterase prior to addition of dopamine enhanced the effect of this amine to decrease baseline muscle tension. 4. The inhibitory effects of 10(-5) M dopamine on the midgut persisted in solutions of zero sodium and in the presence of tetrodotoxin. Zero calcium solutions gradually reduced spontaneous midgut activity and the effects of dopamine. Calcium channel blockers did not prohibit dopamine-induced relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Catecholamines; Chromatography, High Pressure Liquid; Cyclic AMP; Cyclic GMP; Digestive System; Dopamine; Electrochemistry; Gastrointestinal Motility; Histocytochemistry; Horseshoe Crabs; In Vitro Techniques; Muscles; Neuropeptides; Octopamine; Oligopeptides

The biochemical mechanisms by which octopamine, catecholamines and the peptide proctolin exert their actions on Limulus cardiac muscle were investigated. Amines produced long-lasting increases in the amplitude of contractions evoked by electrical stimulation. At 10(-5) mol l-1, the apparent order of potency for amine-induced increases in evoked contraction amplitude was dopamine approximately equal to octopamine greater than norepinephrine approximately equal to epinephrine. At this dose, amines produced long-lasting increases in the levels of cyclic AMP (octopamine greater than dopamine approximately equal to norepinephrine approximately equal to epinephrine), but not of cyclic GMP, in Limulus cardiac muscle. Like the amines, the adenylate cyclase activator forskolin enhanced cardiac muscle contractility and increased levels of cyclic AMP, but not of cyclic GMP. The phosphodiesterase inhibitor IBMX produced a transient increase in cardiac muscle contractility, but typically produced long-lasting negative inotropy. This agent increased levels of both cyclic AMP and cyclic GMP in Limulus cardiac muscle. Proctolin and the protein kinase C activator phorbol dB increased the contraction amplitude of the intact heart and the electrically stimulated myocardium. These compounds, as well as dopamine, elicited sustained contractures and rhythmic contractions when applied to deganglionated Limulus cardiac muscle rings. Unlike the amines, proctolin and phorbol dB did not increase cardiac muscle cyclic AMP levels. These results suggest that several second-messenger systems may be utilized by amines and peptides to produce excitatory actions on cardiac muscle fibers of the Limulus heart. Cyclic AMP appears to be an important second messenger underlying the effects of amines to enhance cardiac muscle contractility. Pharmacological data suggest that proctolin may alter cardiac muscle contractility and excitability by a mechanism which involves the phosphatidylinositol pathway. Dopamine, unlike the other amines, produces a number of proctolin-like effects and may activate both the cyclic AMP and the phosphatidylinositol systems in Limulus cardiac muscle.

Topics: 1-Methyl-3-isobutylxanthine; Amines; Animals; Catecholamines; Colforsin; Cyclic AMP; Cyclic GMP; Dose-Response Relationship, Drug; Epinephrine; Heart; Horseshoe Crabs; Myocardial Contraction; Neuropeptides; Norepinephrine; Oligopeptides; Peptides; Phorbol 12,13-Dibutyrate; Protein Kinase C; Second Messenger Systems