Elevated cytosolic ca2+ is not required in purinergic-mediated
inhibition of na,k-atpase in proximal tubule cells.
Jin, Wenwu, and Ulrich Hopfer.
Department of Physiology and Biophysics, School of Medicine, Case
Western Reserve University, Cleveland, OH 44106-4970
APStracts 3:0328C, 1996.
The involvement of cytosolic Ca 2+ ([Ca 2+ ] i ) as messenger for the
regulation of Na,K-ATPase activity was investigated in a renal cell
line recently developed by immortalization of early proximal tubule
primary cultures from the Wistar-Kyoto (WKY) rat strain. Na,K-ATPase
was measured as short-circuit current (Isc) in intact monolayers
after permeabilization of the apical plasma membrane with
amphotericin B. With symmetrical solutions, Isc quantitatively
reflects Na,K-ATPase activity as judged by ouabain inhibition and
dependence on Na + and K + . Extracellular ATP (EC 50 = 0.32 mM) on
the apical side produced acute inhibition of Na,K-ATPase generated
Isc of up to 50%. The inhibition peaked within 1 min and lasted about
5 min. The potency order was ATP > ADP >> AMPPCP
= UTP, consistent with a P 2y receptor. Extracellular ATP also
stimulated a transient increase in [Ca 2+ ] i . This increase had a
similar time course as the inhibition of ATPase and reached a peak
change of about 120 nM. However, the elevation of [Ca 2+ ] i is not
required in the purinergic inhibition of the Na,K-ATPase, since
firstly, increases in [Ca 2+ ] i produced with a Ca 2+ ionophore
(ionomycin), failed to mimic the purinergic inhibition; secondly,
BAPTA which abolished the [Ca 2+ ] i elevation failed to block the
purinergic inhibition.
Received 8 February 1996; accepted in final form 11 October 1996.
APS Manuscript Number C76-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996