Intracellular protons inhibit a cloned rat kidney outer medulla k+ channel
expressed in xenopus oocytes.
Tsai, T. D., Shuck, M. E.,+ Thompson, D. P., Bienkowski, M. J. and Lee, K. S.
Cardiovascular Pharmacology, Cell Biology, and Animal Health Therapeutics.
The Upjohn Laboratories, Kalamazoo, MI 49007
APStracts 2:0028C, 1995.
The pH sensitivity of a cloned rat kidney K+ channel, ROMK1, was examined
following expression in Xenopus oocytes. Membrane currents and intracellular
pH 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
inward-rectifying, Ba2+ sensitive K+ current. Lowering external pH from 7.4
to 6.7 using membrane permeable acetate buffer reduced measured intracellular
pH 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 intracellular pH fitted to a titration curve suggested
binding of four H+ ions 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.
Received 6 October 1994; accepted in final form 15 November 1994
APS Manuscript Number C0599-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1994 The American Physiological Society.
Published in APStracts on 27 February 1995.