title: Intracellular H+ inhibits a cloned rat kidney outer medulla K+ channel expressed in Xenopus oocytes.
abstract: The pH sensitivity of a cloned rat kidney K+ channel, ROMK1, was examined after expression in Xenopus oocytes. Membrane currents and intracellular pH (pHi) were concomitantly monitored by the two-microelectrode voltage-clamp technique and a pH-sensitive microelectrode. Oocytes injected with ROMK1 cRNA developed a hyperpolarized resting potential of -98.7 +/- 0.98 mV and a slightly inwardly rectifying Ba(2+)-sensitive K+ current. Lowering external pH from 7.4 to 6.7 using membrane-permeable acetate buffer reduced measured pHi from 7.2 to 6.6 and reduced the ROMK1 current by 80%. The H+ blockade of ROMK1 currents was voltage independent. The relationship between ROMK1 slope conductance and pHi fitted to a titration curve suggested binding of four H+ to a site with a pK of 6.79. Extracellular acidification from pH 7.4 to 6.0 using membrane-impermeable biphthalate buffer had no effect on the ROMK1 current. The pH sensitivity of the ROMK1 channel is similar to that reported for a small-conductance native kidney K+ channel.
authors.affiliation: Upjohn Laboratories, Kalamazoo, Michigan 49007, USA.
authors.forename: T D
authors.initials: TD
authors.lastname: Tsai
authors.forename: M E
authors.initials: ME
authors.lastname: Shuck
authors.forename: D P
authors.initials: DP
authors.lastname: Thompson
authors.forename: M J
authors.initials: MJ
authors.lastname: Bienkowski
authors.forename: K S
authors.initials: KS
authors.lastname: Lee
mesh_terms: D000085:Acetates / Q000494:pharmacology; D019342:Acetic Acid; D000818:Animals; D001464:Barium / Q000494:pharmacology; D003001:Cloning, Molecular; D004594:Electrophysiology; D006859:Hydrogen / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism*; D007679:Kidney Medulla / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism; D018075:RNA, Complementary / Q000378:metabolism; D051381:Rats; D014982:Xenopus laevis
chemical_list: D000085:Acetates; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D018075:RNA, Complementary; D001464:Barium; D006859:Hydrogen; D019342:Acetic Acid