AJP - Renal Physiology, Vol 250, Issue 4 644-F648, Copyright © 1986 by American Physiological Society
Evidence for electroneutral sodium chloride transport in rat proximal convoluted tubule
K. J. Howlin, R. J. Alpern, C. A. Berry and F. C. Rector Jr
One- to two-thirds of NaCl absorption in the late proximal convoluted
tubule (no luminal organic solutes present) is inhibited by cyanide and
thus is dependent on active transport. To examine whether this active
transport-dependent NaCl transport is electrogenic or electroneutral, the
effect of cyanide on transepithelial potential difference (PD) was measured
in the rat proximal convoluted tubule microperfused in vivo. In the
presence of an ultrafiltrate-like luminal perfusate containing glucose and
alanine, cyanide addition caused the transepithelial PD to change from
-0.44 +/- 0.04 to -0.05 +/- 0.03 mV (P less than 0.001). In the presence of
a late proximal tubular fluid (high chloride, low bicarbonate, no
organics), the transepithelial PD was 1.23 +/- 0.06 mV and was unchanged at
1.19 +/- 0.05 mV after cyanide addition (NS). To eliminate the possibility
that an effect of cyanide on a putative acidification-dependent
lumen-positive PD was concealing an effect on an electrogenic sodium
transport-dependent lumen-negative PD, the above studies were repeated in
the presence of acetazolamide. Cyanide did not affect the transepithelial
PD (1.17 +/- 0.05 vs. 1.07 +/- 0.06 mV, NS). We conclude that, although
cyanide-inhibitable NaCl transport is electrogenic in the presence of
luminal organic solutes, it does not generate a transepithelial PD in their
absence and therefore is electroneutral.
