ROLE OF CL- IN ELECTROGENIC H+ SECRETION BY CORTICAL DISTAL TUBULE

The presence of an electrogenic H+-ATPase has been described in the la te distal tubule, a segment which contains intercalated cells. The pre sent paper studies the electrogenicity of this transport mechanism, wh ich has been demonstrated in turtle bladder and in cortical collecting duct. Transepithelial PD (V-t) was measured by means of Ling-Gerard m icroelectrodes in late distal tubule of rat renal cortex during in viv o microperfusion. The tubules were perfused with electrolyte solutions to which 2 x 10(-7) M bafilomycin or 3.6 x 10(-8) M concanamycin were added. No significant increase in lumen-negative V-t upon perfusion w ith these inhibitors as compared to control, was observed as well as w hen 10(-3) M amiloride, 10(-5) M benzamil or 3 mM Ba2+ were perfused a lone or in combination. The effect of an inhibition of electrogenic H secretion, i.e., increase in lumen-negative V-t by 2-4 mV, was observ ed only when Cl- channels were blocked by 10(-5) M 5-nitro-2-(3-phenyl propylamino) benzoic acid (NPPB). This blocker also reduced the rate o f 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 m icroperfusion 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 V-t is mi nor in physiological conditions, but can be demonstrated after blockin g 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- chan nel blocker, supporting coupling of H+-ATPase with Cl- transport.