Role of Cl- in electrogenic H+ secretion by cortical distal tubule

The presence of an electrogenic H+-ATPase has been described in the late distal tubule, a segment which contains intercalated cells. The present paper studies the electrogenicity of this transport mechanism, which has been demonstrated in turtle bladder and in cortical collecting duct. Transepithelial PD (Vt) was measured by means of Ling-Gerard microelectrodes in late distal tubule of rat renal cortex during in vivo microperfusion. The tubules were perfused with electrolyte solutions to which 2 x 10(-7) M bafilomycin or 4.6 x 10(-8) M concanamycin were added. No significant increase in lumen-negative Vt upon perfusion with these inhibitors as compared to control, was observed as well as when 10(-3) m amiloride, 10(-5) M benzamil or 3 mM Ba2+ were perfused alone or in combination. The effect of an inhibition of electrogenic H+ secretion, i.e., increase in lumen-negative Vt by 2-4 mV, was observed only when Cl- channels were blocked by 10(-5) M 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB). This blocker also reduced the rate of bicarbonate reabsorption in this segment from 1.21 +/- 0.14 (n = 8) to 0.62 +/- 0.03 (8) nmol.cm-2.sec-1 as determined by stationary microperfusion and pH measurement by ion-exchange resin microelectrodes. These results indicate that: (i) the participation of the vacuolar H+ ATPase in the establishment of cortical late distal tubule Vt is minor in physiological conditions, but can be demonstrated after blocking Cl- channels, thus suggesting a shunting effect of this anion; and, (ii) the rate of H+ secretion in this segment is reduced by a Cl- channel blocker, supporting coupling of H+-ATPase with Cl- transport.