AJP - Cell Physiology, Vol 262, Issue 5 C1161-C1166, Copyright © 1992 by American Physiological Society
Verapamil blocks basolateral K+ channels in the larval frog skin
S. D. Hillyard and W. Van Driessche
Department of Biological Sciences, University of Nevada, Las Vegas 89154.
The short-circuit current (Isc) across isolated skin from larval frogs
(Rana catesbeiana) was measured when the tissue was bathed with Na2SO4
Ringer solution on the serosal side and with a Ringer solution containing
K+ as the primary cation on the mucosal side. When 150 U/ml nystatin was
added to the mucosal solution, the Isc increased from 1.4 +/- 0.1 to 35.4
+/- 4.8 microA/cm2. When verapamil was added to the mucosal and serosal
Ringer solutions in concentrations between 2.5 and 80 microM, Isc was
inhibited in a stepwise manner. At 80 microM, Isc was reduced by 75.3% to
8.74 +/- 1.14 microA/cm2. Analysis of the inhibition of Isc with the direct
linear plot method showed that the blockage of Isc could be described by
pseudo-first-order kinetics with a Michaelis constant (Km) of 9.59 +/- 2.20
microM. Fluctuation analysis revealed a Lorentzian component in power
spectra obtained from preparations treated with 10-80 microM verapamil. The
corner frequency of these Lorentzian components increased in a linear
manner over this range of verapamil concentrations. The Km calculated from
the ratio of the dissociation and association rate constants (k10/k'01) was
39.5 microM. The single-channel currents (i) calculated from the
fluctuation analysis parameters decreased significantly between verapamil
concentrations of 10 and 80 microM. It appears that the inhibition of K+
channels in the basolateral membrane of this tissue has at least two
components.(ABSTRACT TRUNCATED AT 250 WORDS)
