Time course of transmitter action at the sympathetic neuroeffector junction in rodent vascular and non-vascular smooth muscle

Abstract

1. Transmitter release from sympathetic postganglionic nerve terminals innervating the guinea-pig and mouse vas deferens and the rat tail artery has been studied in vitro by focal extracellular recording with particular emphasis on the time course of transmitter action underlying the intracellular potential changes. 2. In the absence of stimulation, spontaneous excitatory junction currents (SEJCs) were recorded with amplitudes up to 500 microV and durations between 40 and 100 ms. SEJCs were unaffected by the competitive alpha-adrenoceptor antagonist prazosin but blocked by alpha, beta-methylene ATP which desensitizes P2-purinoceptors. 3. During trains of supramaximal stimuli at 0.1-4 Hz stimulus locked excitatory junction currents (EJCs) were evoked intermittently from the population of varicosities located under the suction electrode. 4. SEJCs were similar in amplitude and time course to EJCs evoked by low-frequency stimulation in the same attachment in all three tissues. 5. SEJCs recorded using either a conventional AC amplifier or a patch clamp amplifier had the same time course. 6. These studies show that the time course of the current underlying the excitatory junction potential is brief and essentially the same in three different tissues. The prolonged time course of the excitatory junction potential in different tissues can be accounted for by the passive membrane properties.