title: Basolateral pH-sensitive K+ channels mediate membrane potential of proximal tubule cells in bullfrog kidney.
abstract: The present study investigated basolateral K+ channels and their pH-sensitivity in isolated bullfrog proximal tubule cells by using the patch-clamp technique, and compared channel activity with the basolateral membrane potential (EM) and intracellular pH (pHi) monitored by using double-barreled H+-selective microelectrodes in perfused bullfrog proximal tubules. In the patch-clamp experiments, K+ channels with inward slope conductance of about 50 pS were observed in the basolateral membrane of isolated proximal tubule cells in cell-attached patches. Raising pH of the bath with HCO3(-)-free HEPES Ringer solutions from 7.7 (control) to 8.2 in the presence of an H+ ionophore, FCCP (2 micro M), enhanced channel activity to 126.4% of controls; lowering bath pH to 7.2 and to 6.7 reduced channel activity to 26.4 and to 1.7% of controls. Microelectrode experiments in bullfrog proximal tubules perfused with HCO3(-) -free HEPES Ringer solutions showed that EM and pHi in control conditions of peritubular pH 7.7 without FCCP were -52.6 mV and 7.45. Raising peritubular pH to 8.2 in the presence of FCCP (2 micro M) increased EM and pHi to -61.8 mV and 7.73; lowering it to 7. 2 and to 6.7 decreased EM and pHi to -28.6 mV and 7.25 and to -10.6 mV and 6.95. These results suggest that changes in EM in response to cellular alkalinization or acidification made by HCO3(-)-free HEPES solutions are produced primarily by changes in activity of the pH-sensitive K+ channels.
authors.affiliation: Department of Physiology, Osaka Medical College, Takatsuki, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Kubokawa
authors.forename: Y
authors.initials: Y
authors.lastname: Mori
authors.forename: K
authors.initials: K
authors.lastname: Fujimoto
authors.forename: T
authors.initials: T
authors.lastname: Kubota
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D017736:Ion-Selective Electrodes; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008839:Microelectrodes; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011892:Rana catesbeiana
chemical_list: D001639:Bicarbonates; D015221:Potassium Channels