Modulation of na+/ca2+ exchange in epithelial cells of the porcine
thick ascending limb.
Dai, Long-Jun, Gordon Ritchie, Brian Bapty, Veronique Auger, and Gary
A. Quamme.
Department of Medicine, University of British Columbia, Vancouver
Hospital and Health Sciences Centre, Koerner Pavilion, Vancouver, BC
Canada
APStracts 2:0212F, 1995.
We have provided functional and molecular evidence for the presence of
Na+/Ca2+ exchange in isolated porcine cortical thick ascending limb
(cTAL) cells. The present studies were designed to show that this
exchange activity may be modulated by phosphorylative processes.
Control of [Ca2+]i was determined in isolated cTAL cells with
microfluorescence. cTAL cells were pretreated with ouabain to elevate
[Na+]i from 10 to 20 mM. These cells had normal basal [Ca2+]i , 79+/
-3 nM. Substitution of extracellular NaCl (50 mM) with KCl resulted in
the rapid elevation of [Ca2+]i to maximal levels of 795+/-60 nM,
n=17. The increments of [Ca2+]i were associated with [Na+]i. We next
determined the modulation of Na+/Ca2+ exchange activity with
phosphorylative inhibitors. Pretreatment of cells with calmidazolium,
a Ca2+-calmodulin inhibitor, resulted in a shift of the [Na+]i
dependence curve to the right. Pretreatment with okadaic acid, a
phosphatase 1 and 2A inhibitor, increased the Na+/Ca2+ exchanger
activity resulting in half maximal [Ca2+]i increase near normal
[Na+]i of 12 mM. Further, in the presence of okadaic acid in normal
cTAL cells, pretreatment with ouabain and the elevation of [Na+]i was
not required to elicit increments in [Ca2+]i. These data indicate
that Na+/Ca2+ exchange is present in cTAL cells and the exchange
activity appears to be modulated, directly or indirectly, by
phosphorylation events.
Received 31 August 1995; accepted in final form 30 November 1995.
APS Manuscript Number F288-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95