REGULATION OF AMILORIDE-SENSITIVE NA+ ABSORPTION IN THE LIZARD (GALLOTIA-GALLOTI) COLON BY ALDOSTERONE

1. Acute (AT) or chronic (CT) administration of exogenous aldosterone brought about a considerable increase in transmural potential difference (PD), short-circuit current (Isc) and net sodium flux (J(net)Na). 2. A good relationship between Isc and J(m-s)Na was observed in CT but not in AT or UC (untreated controls). 3. Addition of mucosal amiloride reduced Isc in AT and CT colons, but did not cause any change in UC colons. The relationship between Isc and J(m-s)Na observed in CT was totally suppressed by the diuretic. 4. J(net)Na was reduced in AT tissues and abolished in CT colons by amiloride. 5. The present results strongly suggest that aldosterone levels quantitatively and qualitatively modify sodium absorption across colonic mucosa in a dose-dependent fashion and that lower levels of the hormone are required to induce the electrogenic Na absorption than to suppress the electroneutral transport.