Fusion of cultured dog kidney (MDCK) cells: II. Relationship between cell pH and K⁺ conductance in response to aldosterone

Summary

We have chosen the MDCK cell line to investigate aldosterone action on H⁺ transport and its role in regulating cell membrane K⁺ conductance (G ^K_m ). Cells grown in a monolayer respond to aldosterone indicated by the dose-dependent formation of domes and by the alkalinization of the dome fluid. The pH sensitivity of the plasma membrane K⁺ channels was tested in “giant cells” fused from individual MDCK cells. Cytoplasmic pH (pH _i ) andG ^K _m were measured simultaneously while the cell interior was acidified gradually by an extracellular acid load. We found a steep signoidal relationship between pH _i andG ^K _m (Hill coefficient 4.4±0.4), indicating multiple H⁺ binding sites at a single K⁺ channel. Application of aldosterone increased pH _i within 120 min from 7.22±0.04 to 7.45±0.02 and from 7.15±0.03 to 7.28±0.02 in the absence and presence of the CO₂/HCO ⁻₃ buffer system, respectively. We conclude that the hormone-induced cytoplasmic alkalinization in the presence of CO₂/ HCO ⁻₃ is limited by the increased activity of a pH _i -regulating HCO ⁻₃ extrusion system. SinceG ^K _m is stimulated half-maximally at the pH _i of 7.18±0.04, internal H⁺ ions could serve as an effective intracellular signal for the regulation of transepithelial K⁺ flux.