ESTIMATION OF THE PHYSICAL STATE OF POTASSIUM IN FROG BLADDER CELLS BY ION EXCHANGER MICROELECTRODE

Publisher Website
Google Scholar
Abstract
Intracellular K+ activity in the epithelium of the isolated bullfrog urinary bladder was measured with a K+-selective liquid ion exchanger microelectrode. Using Ussing''s apparatus, the short circuit current (SCC) and the potential difference (PD) across the bladder were also determined in Ringer solution on both sides of the epithelium with or without certain metabolic inhibitors. The mean values obtained from 76 control experiments were -25.1 mV for PD (the mucosal side negative) and 49.3 .mu.A for the SCC (current from the mucosal to the serosal side). The serosal and mucosal membrane potential (sEm and mEm) was -12.4 and 12.7 mV with respect to the serosal and mucosal surface, respectively. The normal intracellular K+ activity was 39.3 mM. Assuming that the intracellular ionic strength was equal to the extracellular one, the predicted K+ concentration was 52 mM. The calculated K+ equilibrium potential, EK, was -67.2 mV with respect to the serosal surface, which was far more negative than the measured value of sEm or mEm. Addition of ouabain to and removal of K+ from the bathing media effectively reduced the intracellular K+ activity in the free form, but not in the bound form. Ethacrynic acid and rotenone markedly depressed the membrane potential disproportionately to the cellular K+. Though significant correlations were observed between PD and SCC, sEm and mEm, and so between SCC and sEm, the EK tended to vary independently of either sEm or SCC. K+ must be actively accumulated into the cell against the electrochemical gradient and more than half of the cellular K may exist in a restricted (bound or compartmentalized) form.

This publication has 3 references indexed in Scilit: