AJP - Renal Physiology, Vol 244, Issue 2 122-F128, Copyright © 1983 by American Physiological Society
Effect of potassium concentration on bicarbonate reabsorption in the rabbit proximal convoluted tubule
S. Sasaki, C. A. Berry and F. C. Rector Jr
The direct effects of acute changes in K+ concentration on HCO-3 (JnettCO2)
and volume reabsorption (Jv) were examined in isolated perfused rabbit
proximal convoluted tubules (PCT). Increasing ambient K+ concentration from
5 to 8 mM did not change JnettCO2 (94.5 +/- 16.1 vs. 98.8 +/- 17.7 pmol X
mm-1 X min-1) or Jv (1.27 +/- 0.15 vs. 1.24 +/- 0.16 nl X mm-1 X min-1). In
contrast, reducing ambient K+ concentration from 5 to 2 mM inhibited
JnettCO2 by 22% and Jv by 29%. Reducing luminal K+ concentration from 5 to
0 mM with constant bath K+ concentration at 5 mM did not affect JnettCO2 or
Jv. Further reductions in bath K+ concentration to 0.5 and 0 mM showed a
similar dependence of both fluxes on K+ concentration. Half-maximum
inhibition of JnettCO2 was obtained at 1.1 mM ambient K+ concentration and
of Jv at 0.85 mM. At zero bath K+ concentration JnettCO2 was 6.6 +/- 2.5
pmol X mm-1 X min-1 and Jv was 0.03 +/- 0.04 nl X mm-1 X min-1. To
determine whether this rate of acidification was significantly different
from zero, we examined the ability of the PCT to generate tCO2
concentration gradients with zero bath K+ concentration at slow perfusion
rates. The tCO2 concentration gradient generated (0.94 mM) was not
different from that found when the perfusate was inserted directly into the
collection pipette in the absence of a tubule (0.71 mM). These data are
consistent with the view that HCO-3 reabsorption is totally dependent on
the Na+-K+-ATPase pump system.
