Effects of apamin on alpha-adrenoceptor-mediated changes in plasma potassium in guinea-pigs

An intravenous K+-sensitive electrode has been used to monitor plasma [K+] changes induced by adrenaline (1.4-6.8 micrograms kg-1) and amidephrine (14-340 micrograms kg-1) in anaesthetized guinea-pigs. A biphasic response consisting of an initial increase in [K+] followed, within 1 min, by a fall below baseline was observed with both agonists. Apamin (0.4-40 micrograms kg-1) reduced the hyperkalaemic phase of the response to amidephrine in a dose-related, non-competitive manner. The response to adrenaline was also reduced but to a lesser extent. Apamin caused little or no reduction of the hypokalaemic phase of the response to either agonist.