Early effects of glucose and oxygen deprivation on the spontaneous acetylcholine release from the myenteric plexus of the guinea pig ileum

Abstract

The early effects of glucose and oxygen deprivation on the spontaneous acetylcholine output from the myenteric plexus – longitudinal muscle preparation of the guinea pig ileum were studied using an incubation chamber that permitted rapid sample collection in 2-min intervals. Glucose deprivation or hypoxia resulted in a gradual decline in rate of spontaneous acetylcholine output. However, glucose deprivation plus hypoxia caused an acceleration in acetylcholine output within 10–15 min, which attained a rate seven times greater than observed under normal conditions. Recovery of low resting rates was obtained by reintroduction of oxygen and glucose into the bath medium. Neither morphine (2.7 × 10−5 M) nor tetrodotoxin (1.6 × 10−6 M) prevented the increase in acetylcholine output induced by energy deprivation. The substitution of Ca2+ by Mg2+, in the presence of EGTA, greatly reduced the acetylcholine output induced by energy deprivation. However, a small transitory output of acetylcholine was observed under these conditions which was resistant to tetrodoxin and not affected by depolarizing amounts of K+. The transitory output was repeatable by reintroduction of glucose and oxygen to the Ca2+-free medium with subsequent return to conditions of hypoxia and glucose deprivation.These results suggest that energy deprivation initially stimulates normal acetylcholine secretion by (a) increasing Ca2+ influx across the plasma membrane and (b) mobilizing an intracellular Ca2+ pool. This implies that processes involved in maintenance of normal low transmitter release are more sensitive to energy lack than the neurosecretion process itself.