Na+/ca2+ exchanger in epithelial cells of the porcine cortical
thick ascending limb.
Dai, Long-Jun, Gordon Ritchie, Brian Bapty, Lynn Raymond, and Gary A.
Quamme.
Departments of Medicine and Psychiatry, University of British
Columbia, VHHSC - Koerner Pavilion, Koerner Pavilion, Vancouver, BC
Canada
APStracts 2:0189F, 1995.
Intracellular Ca2+ concentration, [Ca2+]i, plays an important role in
the signal transduction processes within cortical thick ascending
limb (cTAL) cells. Control of [Ca2+]i was investigated in isolated
cTAL cells with microfluorescent techniques. cTAL cells pretreated
with ouabain to elevate [Na+]i had basal [Ca2+]i, of 86+/-2 nM.
Removal of extracellular Na+o or voltage depolarization with KCl (in
the presence of Na+o) resulted in a rapid and reversible maximal
elevation of [Ca2+]i, 1023+/-72 nM, n=28, which was dependent on the
presence of external Ca2+o. The rise in [Ca2+]i was inhibited with
La3+, Mg2+, amiloride, and bepridil. The increments of [Ca2+]i with
either removal of Nao or voltage depolarization was dependent on
pretreatment with ouabain and increases in [Na+]i. The presence of a
Na+/Ca2+ exchanger was confirmed with hybridization techniques and
the isoform identified by sequencing the alternative splicing site
within the intracellular loop. A gene transcript which encodes a
portion of the intracellular loop of the renal Na+/Ca2+ exchanger was
amplified from cortical tissue and single cTAL cells by RT-PCR, using
primers flanking the alternative splicing site. Southern
hybridization and DNA sequencing demonstrated the isoform contained
exons B and D which is characteristic of one isoform (NACA3) of the
renal Na+/Ca2+ exchanger. The results provide both functional and
molecular evidence for a Na+/Ca2+ exchanger in thick ascending limb
cells of the porcine kidney.
Received 27 April 1995; accepted in final form 11 September 1995.
APS Manuscript Number F141-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95