Effects of acetaldehyde on electrical activity during neuroeffector transmission in guinea-pig vas deferens.

The effects of acetaldehyde on electrical activity during sympathetic neuroeffector transmission were studied in the guinea-pig vas deferens. Application of 1 mM acetaldehyde produced a slow depolarization of the smooth muscle membrane. The amplitudes of facilitated excitatory junction potentials (EJPs) evoked by nerve stimulation were slightly decreased. A higher concentration of acetaldehyde (5 mM) initially hyperpolarized and later depolarized the membrane. The decrease in EJP amplitudes was more pronounced during hyperpolarization. Acetaldehyde (5 mM) increased the frequency of the spontaneous EJPs and reduced their amplitudes, whereas action potentials in postganglionic nerves were unaffected. Acetaldehyde (1-5 mM) decreased the amplitudes of EJPs in vasa pretreated with reserpine but did not alter the resting membrane potentials. The decrease in the EJP amplitudes together with the hyperpolarization of the membrane could be responsible for the early inhibitory effect of acetaldehyde on neuroeffector transmission. The slow depolarization, which is presumably mediated by endogenous noradrenaline, may cause the late facilitatory effect.