Aldosterone regulation of active sodium chloride transport in the lizard colon (Gallotia galloti)

Abstract

Bioelectrical parameters and unidirectional sodium and chloride fluxes were measured under voltageclamp conditions in groups of lizards submitted to single or chronic aldosterone treatment. Both acute (AT) and chronic (CT) treatment induced significant increases in the short-circuit current (Isc), as well as in the mucosa-to-serosa (Jm-sNa) and net sodium flux (JnetNa). In AT tissues, aldosterone did not change net chloride flux (JnetCl) but did so in CT tissues. Amiloride reduced the aldosterone-increased Isc in AT and CT tissues, inhibited JnetNain AT tissues and abolished it in CT colons. JnetClwas also reduced by the diuretic in the group of AT colons, whereas no changes were observed in the CT tissues. Addition of luminal DIDS reduced Na+ absorption and totally inhibited Cl- absorption in the AT tissues, but did not change Isc. However, in CT tissues neither Na+ nor Cl- transport were affected by DIDS. A good relationship between Isc and Jm-sNawas apparent after DIDS treatment in AT tissues. In this group, simultaneous addition of DIDS and amiloride totally abolished JnetNaand reduced Isc to untreated control values. Addition of serosal ouabain abolished Isc and Na+ absorption in AT and CT colons, but Cl- absorption was only altered in AT tissues. These results support the hypothesis that aldosterone induces an electrogenic, amiloride-sensitive sodium absorption, and in a dose-dependent fashion suppresses electroneutral NaCl absorption in the lizard colon.