Biology Of Sodium‐Absorbing Epithelial Cells: Dawning of a New Era

The effect of cAMP on electrogenic Na(+) absorption in the rat distal colon

Cyclic AMP is a ubiquitous second messenger produced in cells in response to extracellular stimulants. The aim of this study was to examine its role in the regulation of amiloride-sensitive electrogenic Na(+) absorption in the rat distal colon by measuring the short-circuit current (I(sc)) and (22)Na(+) fluxes in a chamber-mounted mucosal sheet. Forskolin stimulated the amiloride-inhibitable I(sc) and amiloride-inhibitable (22)Na(+) absorption. 8Br-cAMP also stimulated the amiloride-inhibitable I(sc). Furthermore, isoproterenol, acting via beta-adrenergic activation, stimulated the amiloride-inhibitable I(sc). The isoproterenol-induced increase in the amiloride-sensitive I(sc) was largely suppressed by H89, a protein kinase A inhibitor. In conclusion, cAMP can upregulate amiloride-sensitive electrogenic Na(+) absorption in the rat distal colon.