cyclic-gmp and cobaltous-chloride

The objective of this study was to investigate the effects of nitroglycerin (NG) on the contractile force in order to elucidate regulatory roles of cyclic guanosine monophosphate (cGMP) in the bundle of canine cardiac Purkinje fibers. NG suppressed the developed tension in canine Purkinje fibers immersed in normal Tyrode's solution. The contraction was also elicited in the depolarizing solution containing 30 mM K+ by adding isoproterenol (Iso) or tetraethylammonium (TEA). The suppression caused by NG was more marked in fibers in the depolarizing solution treated with TEA than in the depolarizing solution treated with Iso. 8-Bromo-cGMP and sodium nitroprusside had a slight inhibition on the contraction in the fibers. Methylene blue did not affect the decrease in contractile force induced by NG. The weaker inhibition caused by NG on the contraction in the presence of Iso might result from a possible increase in intracellular cAMP levels in the fibers.

Topics: Animals; Cardiotonic Agents; Cobalt; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Dogs; Dose-Response Relationship, Drug; Electric Stimulation; Enzyme Inhibitors; Guanylate Cyclase; In Vitro Techniques; Isoproterenol; Methylene Blue; Muscle Strength; Myocardial Contraction; Nitric Oxide Donors; Nitroglycerin; Nitroprusside; Potassium; Potassium Channel Blockers; Purkinje Fibers; Tetraethylammonium