On the time course of the acetylcholine-induced hyperpolarization in quiescent guinea-pig atria.
The time course of the action of acetylcholine (ACh) released from postganglionic parasympathetic nerve endings was studied in quiescent preparations of right atria from the guinea-pig heart. ACh release was induced by stimulation with single impulses subthreshold for excitation of atrial muscle cells. After stimulation a hyperpolarization of the atrial cell membrane could be recorded. At 35 degrees C time to peak (ttp) was reached 580--890 ms after the stimulus pulse. The hyperpolarization declined exponentially with a time constant of 1.6--3.4 s. The early rising phase was proportional to t3 where t is time and displayed a Q10 of about 12. The decay was less temperature-dependent (Q10 of ca. 1.5). Superfusion with solutions containing caffeine (0.25--2.0 mM) an inhibitor of cyclic nucleotide phosphodiesterases resulted in a prolongation of ttp, a flattering of the hyperpolarization maximum and an increase of the time constant of decay. It is suggested that a least three successive reactions are involved in the formation of ionic conductance channels after ACh receptor interaction. The results obtained with caffeine support the idea that formation of a cyclic nucleotide might participate in muscarinic action of ACh in the atrium.
D000109:Acetylcholine / Q000502:physiology*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D004594:Electrophysiology; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects / Q000294:innervation*; D006325:Heart Atria / Q000187:drug effects / Q000294:innervation; D066298:In Vitro Techniques; D010275:Parasympathetic Nervous System / Q000502:physiology; D011950:Receptors, Cholinergic / Q000502:physiology*
D011950:Receptors, Cholinergic; D002110:Caffeine; D000109:Acetylcholine