Distinct regulation of Na+ reabsorption and Cl- secretion by arginine vasopressin in the amphibian cell line A6

The neurohypophysial peptide arginine vasopressin (AVP) increases Na+ absorption across A6 epithelia. In addition to the positive natriferic response, AVP increases net basolateral to apical Cl- flux. The time course of activation of electrogenic ion transport in A6 epithelia was examined by measuring transepithelial short-circuit current (ISC). Basolateral application of AVP (0.1 U/ml) or forskolin (10 microM) affects ISC in a biphasic manner. Shortly after addition of AVP, an early (transient) phase is observed in which ISC is rapidly stimulated, reaching a peak value at 1.4 +/- 0.1 min. A subsequent decrease in current is interrupted by a slower, late phase in which ISC reaches a peak 23 +/- 3 min after addition of AVP. The late increase in ISC is sustained over the remainder of the 40-min period of observation. The time course of ISC stimulation by forskolin is qualitatively similar. Replacement of external Cl- by aspartate lowers baseline transport nearly 40%, strongly blunts the early phase of ISC stimulation, and retains the late increase. Addition of amiloride (10 microM) to the apical bath before AVP or forskolin stimulation of ISC eliminates the late increase of ISC. Steady-state amiloride-insensitive ISC activated under these conditions was sensitive to apical application of the Cl- channel blockers 5-nitro-2-(3-phenylpropylamino)-benzoate (20 microM) and niflumic acid (100 microM). 4,4'-Diisothiocyanostilbene-2,2'-disulfonic acid (1 mM) was not an effective inhibitor of this current. Basolateral bumetanide (100 microM) inhibited baseline ISC and reduced both the peak transient and steady-state amiloride-insensitive ISC.(ABSTRACT TRUNCATED AT 250 WORDS)