Luminal influences on potassium secretion: transepithelial voltage.

In vivo microperfusion techniques were used to evaluate whether changes in luminal fluid flow rate affect late distal tubule transepithelial voltage (VTE) and to determine whether flow-dependent changes in K secretion by the renal distal tubule of the rat that we observed previously could be attributed to changes in electrical driving forces. Results showed that increasing the perfusion rate from 6 to 26 nl/min of solutions containing either 94, 46, or 15 mM sodium and 2 mM potassium caused VTE to become 10-12 mV less lumen negative. Since increasing perfusion rate decreases VTE, a flow-dependent voltage change is not responsible for the effect of increasing luminal flow rate to increase distal K secretion. To evaluate the possible contribution of changes in luminal Na and K concentrations to the flow-dependent changes in VTE, the effects of changing either Na or K concentration at constant flow rate were examined. These studies showed that 1) changes in luminal Na concentration within the physiological range (44-94 mM) have no detectable effect on VTE; 2) increases in luminal K concentration within the physiological range (5-16 mM) significantly increase VTE; and 3) the flow-dependent depolarization of VTE is primarily caused by flow-dependent changes in luminal K concentration.