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 th e release of adenosine 5'-triphosphate (ATP) and noradrenaline (NA) fr om sympathetic nerves during stimulation with trains at 20 Hz (tetanus ). In mouse vas deferens ATP release was mainly facilitated during the tetanus, but in rat tail artery progressively and reversibly depresse d. In rat tail artery reduction of external calcium attenuated the dep ression and increased the facilitation during the tetanus, while incre ased external calcium accentuated the depression. Both ATP and NA rele ase were depressed in parallel during the first 100 pulses of the teta nus. The depression of release was not due to action potential failure , or alpha2-adrenoceptor-mediated autoinhibition.