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

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Abstract
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 Km ). 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.