Unique localization of mrna encoding plasma membrane ca2+ pump
isoform three in rat thin descending loop of henle.
Caridea, Ariel J., Eduardo N. Chinib, Mario Yamakib, Thomas P. Dousab,
and John T. Pennistona.
Department of Biochemistry and Molecular Biologya and Nephrology
Research Unitb, Division of Nephrology and Internal Medicine,
Departments of Medicine and Physiology, Mayo Clinic/Foundation, 200
First Street South West, Rochester, MN 55905 U.S.A.
APStracts 2:0086F, 1995.
n our previous study of plasma membrane Ca2+ pump (PMCA) isozymes in
the rat kidney, we found that the mRNA coding isoform PMCA3 was
detected primarily in the outer medullary zone of rat kidney tissue.
We now investigated the location of the mRNAs coding for isoforms
PMCA3 and PMCA4 of Ca2+ pump in the nephron segments which are
present in outer medullary parenchyma using the method of reverse
transcription and polymerase chain reaction. In mRNA extracted from
whole dissected outer medulla we detected mRNA encoding three splice
variants (a, b, and c) of isoform PMCA3; isoform PMCA4 was found in
the outer medulla almost exclusively as variant b. Analysis of mRNA
from microdissected tubule segments show that proximal straight
tubules (PST), medullary thick ascending limbs (MTAL), outer
medullary collecting ducts (OMCD), and descending thin limb of Henle
s loop (DTL) all contained mRNA for isoform 4b. In contrast, the mRNA
encoding isoform 3 was detected exclusively in DTL and not in other
nephron segments. The unique presence of isoform 3 in DTL is rather
surprising, since the specific role of this nephron segment in
vectorial Ca2+ transport or in intracellular Ca2+ signalling is not
known. The data suggest that isoform 3 in cells of the DTL may have a
hitherto unrecognized specific role in Ca2+ signalling or transport
of Ca2+, which is distinct from the role of the isoforms of the
plasma membrane Ca2+ pump in all other nephron segments.
Received 1 March 1995; accepted in final form 11 May 1995.
APS Manuscript Number F69-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 26 May 1995.