Nicotinic and muscarinic responses of embryonic chick ventricular myocardium to acetylcholine: chronotropic and electrophysiological effects.
Sensitivity of 7-day-old chick embryo ventricular heart fragments to acetylcholine was investigated. Low doses mainly produced a positive chronotropic effect, whereas high doses of acetylcholine provoked a decrease in the heart beat rhythm. The positive chronotropic effect of acetylcholine was related to the presence of nicotinic receptors that were evidenced within ventricular myocardium by autoradiography. Membrane potential recording showed that acetylcholine hyperpolarizes the diastolic membrane potential when the drug had a negative chronotropic effect. This effect of acetylcholine on the membrane potential was not observed when the drug had a positive chronotropic effect. In many cases, the diastolic membrane potential exhibited spontaneous small depolarizing potentials. Their amplitude was low and their frequency was irregular. These potentials were suppressed by treatment with alpha-bungarotoxin, suggesting that they are triggered by nicotinic receptor activation.
Suignard-Khaskiye
G
G
Groupe de Physiologie Cellulaire, Faculté des Sciences, Nantes, France.
Renaud
D
D
Le Douarin
G
G
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001345:Autoradiography; D002642:Chick Embryo; D004594:Electrophysiology; D006339:Heart Rate / Q000187:drug effects; D006352:Heart Ventricles / Q000187:drug effects; D007457:Iodine Radioisotopes; D011976:Receptors, Muscarinic / Q000032:analysis / Q000502:physiology*; D011978:Receptors, Nicotinic / Q000032:analysis / Q000502:physiology*; D016276:Ventricular Function
D007457:Iodine Radioisotopes; D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic; D000109:Acetylcholine