title: Ca2+-activated K+ channels from cultured renal medullary thick ascending limb cells: effects of pH.
abstract: Ca2+-activated K+ channels were studied in cultured medullary thick ascending limb cells (MTAL) using the patch-clamp technique. The purpose was to determine the effect of acidic pH on channel properties in excised patches of apical cell membrane. At pH 7.4, increasing Ca2+ on the intracellular side or applying positive voltages increases channel open probability. Reducing pH to 5.8 on the intracellular face of the channel decreases channel open probability at each voltage and Ca2+ concentration. Channel mean open times display two distributions and mean closed times display three distributions. Increasing Ca2+ or applying depolarizing voltages lengthens each of the mean open times and shortens each of the closed times. Lowering pH to 5.8 decreases the mean open times and increases mean closed times at each Ca2+ and voltage with the greatest effect on the mean closed times. In contrast, both single-channel conductance and channel kinetics are unaffected when pH is reduced to 5.8 on the extracellular face of the membrane. We conclude that protons interfere with Ca2+ binding to the gate of Ca2+-activated K+ channels reducing the probability of channel opening.
authors: Department of Physiology, Johns Hopkins University, School of Medicine, Baltimore, Maryland 21205.
authors: M
authors: M
authors: Cornejo
authors: S E
authors: SE
authors: Guggino
authors: W B
authors: WB
authors: Guggino
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002462:Cell Membrane / Q000378:metabolism / Q000502:physiology / Q000648:ultrastructure; D002463:Cell Membrane Permeability / Q000187:drug effects; D002478:Cells, Cultured; D004553:Electric Conductivity; D006859:Hydrogen / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating / Q000502:physiology; D007684:Kidney Tubules; D007686:Kidney Tubules, Distal / Q000166:cytology* / Q000502:physiology / Q000648:ultrastructure; D011188:Potassium / Q000378:metabolism / Q000493:pharmacokinetics; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D011817:Rabbits
chemical_list: D015221:Potassium Channels; D006859:Hydrogen; D011188:Potassium; D002118:Calcium