FURTHER CHOLINERGIC ASPECTS OF CAROTID-BODY CHEMOTRANSDUCTION OF HYPOXIA IN CATS

From the 1930s into the 1970s, the role of acetylcholine (ACh) in the carotid body's chemotransduction of hypoxia was debated. Since the lat e 1970s, the issue has been pursued only intermittently or not at all. The purpose of this study was to test again with a new preparation th e hypothesis that ACh is an excitatory neurotransmitter in the cat car otid body's chemotransduction of hypoxia. We tested the effect of the specific nicotinic blocker mecamylamine and the muscarinic blocker of all five muscarinic receptors, atropine. We further tested the effects of M(1) and M(2) muscarinic-receptor blockers. The carotid body regio n was selectively perfused with hypoxic Krebs-Ringer bicarbonate (KRB) solutions that were blocker free or contained varying doses of the bl ockers. Both mecamylamine and atropine reduced the response to hypoxic KRB in a dose-related manner. The M(2) muscarinic-receptor blockers g allamine and AFDX 116 increased the response to hypoxic KRB, whereas t he M(1) muscarinic-receptor blocker pirenzepine reduced the response t o hypoxic KRB. These data are consistent with an excitatory role for A Ch in the carotid body chemotransduction of hypoxia in the cat.