title: Effects of 8-bromo-cyclic GMP on contraction and on inotropic response of ferret cardiac muscle.
abstract: The effects of guanosine 3':5'-cyclic monophosphate (cGMP) on cardiac contraction are not established. Using isolated electrically-stimulated ferret papillary muscle at 29 degrees C, 2.0 mM calcium we investigated the effects of 8-Bromo-cGMP on (a) basal contraction for comparison with the effects of reduction in extracellular calcium or of reduction in resting muscle length; (b) contraction of preparations stimulated by isoprenaline, the dihydropyridine calcium agonist Bay K8644 or post-extrasystolic potentiation. 8-Bromo-cGMP (0.1 mM) induced a small significant reduction in isometric twitch tension (TT) (7%), isotonic shortening (PS) (6%) and in twitch duration, but had no effect on maximum unloaded shortening velocity (Vmax) or rate of tension development (+dT/dt). Reduction in muscle length induced a similar immediate effect on contraction. Reduction of extracellular calcium (2.0 mM to 1.25 mM) reduced TT by 24% and PS by 14% as well as Vmax (19%) and +dT/dt (29%), but did not alter twitch duration. Bay K8644 (0.01 to 10 microM) produced increases in TT, +dT/dt, PS and twitch duration each of which was significantly reduced in the presence of 8-Bromo-cGMP (0.1 mM). 8-Bromo-cGMP had no effect on the responses to isoprenaline 1 nM to 100 microM--which increased TT, +dT/dt and PS but markedly reduced twitch duration--nor on post-extrasystolic potentiation which increased TT and +dT/dt but slightly reduced twitch duration. These results show that 8-Bromo-cGMP induces changes similar to the immediate effects of reduction in resting muscle length, and reduces the positive inotropic effects of Bay K8644 but not those of isoprenaline or post-extrasystolic potentiation.
authors.affiliation: Department of Cardiology, University of Wales College of Medicine, Heath Park, Cardiff, UK.
authors.forename: A M
authors.initials: AM
authors.lastname: Shah
authors.forename: M J
authors.initials: MJ
authors.lastname: Lewis
authors.forename: A H
authors.initials: AH
authors.lastname: Henderson
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005289:Ferrets; D007545:Isoproterenol / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects*; D010210:Papillary Muscles / Q000187:drug effects / Q000502:physiology
chemical_list: C016276:8-bromocyclic GMP; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D006152:Cyclic GMP; D007545:Isoproterenol; D002118:Calcium