Effects of ba2+ and cs+ on the apical membrane k+ conductance in the toad
retinal pigment epithelium.
Hughes, Bret A., Ahsan Shaikh, and Amjad Ahmad.
Departments of Ophthalmology and Physiology, University of Michigan, Ann
Arbor, MI 48105
APStracts 2:0061C, 1995.
Intracellular microelectrode techniques were employed to characterize the
blocker sensitivity of the K+ conductance (gK) at the apical membrane of the
toad retinal pigment epithelium. Increasing the K+ concentration in the
apical bath ([K+]o) from 2 to 5 mM produced a rapid depolarization of
the apical membrane potential (VA). The addition of 0.5 mM Ba2+ or 5 mM Cs+
to the apical bath rapidly depolarized VA and increased the transepithelial
resistance and ratio of apical-to-basolateral membrane resistance. In the
presence of apical Ba2+ or Cs+, the response of VA to D[K+]o was
markedly reduced, indicating that these ions are effective blockers of apical
gK. The Ba2+- and Cs+-induced decreases in the apparent apical-to-basolateral
membrane conductance ratio were concentration dependent, with apparent
dissociation constants of 17 [mu]M and 0.5 mM, respectively. The apparent
blocker sensitivity of apical gK is similar to that previously demonstrated
for the inwardly rectifying K+ conductance in isolated toad RPE cells,
suggesting that an inwardly rectifying K+ conductance comprises much of
apical gK.
Received 23 September 1994; accepted in final form 30 November 1994.
APS Manuscript Number C574-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 27 February 1995.