Intracellular pH and membrane potassium conductance in rabbit distal colon

Intracellular pH (pH(c)) was measured in the short-circuited epithelium of rabbit distal colon using H⁺-selective microelectrodes. pH(c) was 6.91 ± 0.02 (SE) when the bath pH was 7.4. Intracellular HCO₃̄ activity (a(HCO₃̄)(c)) was estimated from these measurements to be 8 ± 0 mM. When we replaced all Cl^- in the tissue bathing solutions with the impermeant anion gluconate, pH(c) rose to 7.44 ± 0.08 and a(HCO₃̄)(c) increased to 30 ± 6 mM. These results demonstrate thast this tissue contains a Cl^--HCO₃̄ exchange mechanism. During the Cl^- replacement the apical membrane electrical potential difference hyperpolarized from -55 ± 1 to -74 ± 3 mV, suggesting that membrane ionic conductance had changed. Elevation of either the apical or basolateral membrane bathing solution K⁺ concentration produced a greater depolarization of membrane potential during Cl^- replacement than when tissues were bathed in normal electrolyte solutions. In additional experiments, pH(c) was raised by lowering the bath CO₂ concentration while the bath Cl^- concentration was kept normal. Under these conditions, membrane potential hyperpolarized and was more sensitive to the elevation of bath K⁺ concentration than when pH(c) was normal. These results suggest that membrane K⁺ conductance in this tissue is increased by intracellular alkalinization.