Feedback regulation of na channels in rat cct - iv. mediation by
activation of pkc.
Frindt, Gustavo, Lawrence G. Palmer, and Erich E. Windhager.
Dept. of Physiology and Biophysics, Cornell University Medical
College, New York, N.Y. 10021
APStracts 2:0169F, 1995.
The hypothesis that feedback inhibition of the apical Na channels in
the cortical collecting tubule is mediated by activation of a Ca2+
-dependent protein kinase was tested using the patch-clamp technique.
Na channel activity was monitored in cell-attached patches in
principal cells of split open rat tubules. Mean number of open
channels (NPo) and single channel current (i) were measured at 37o C
during continuous tubule superfusion. Phorbol 12-myristate 13-acetate
(PMA) (50 nM), an activator of protein kinase C (PKC), decreased NPo
to 33% of the control value. Staurosporine (200 nM), an inhibitor of
PKC and of Ca2+/CaM kinase II, practically abolished the effect of
PMA. Ouabain (1 mM), reduced NPo to 29% of control values and
decreased i. Ouabain did not down-regulate the channels in tubules
exposed to staurosporine although it still reduced i. Incubation of
the tubules with 10 [mu]M KN-62, a specific cell-membrane-permeable
inhibitor of Ca/Cam kinase II, did not interfere with the ouabain
-dependent downregulation of the channels. The results support the
view that the downregulation caused by ouabain involves the Ca2+
-dependent phosphorylation of the channel itself or of proteins
regulating the channel.
Received 15 March 1995; accepted in final form 11 September 1995.
APS Manuscript Number F90-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 31 October 95