Sympathetic transmitter release in rat tail artery and mouse vas deferens: facilitation and depression during high frequency stimulation.

Electrophysiological and electrochemical methods were used to study the release of adenosine 5'-triphosphate (ATP) and noradrenaline (NA) from sympathetic nerves during stimulation with trains at 20 Hz (tetanus). In mouse vas deferans ATP release was mainly facilitated during the tetanus, but in rat tail artery progressively and reversibly depressed. In rat tail artery reduction of external calcium attenuated the depression and increased the facilitation during the tetanus, while increased external calcium accentuated the depression. Both ATP and NA release were depressed in parallel during the first 100 pulses of the tetanus. The depression of release was not due to action potential failure, or alpha 2-adrenoceptor-mediated autoinhibition.