Cellular Calcium Transport in Renal Epithelia: Measurement, Mechanisms, and
Regulation.
Friedman, Peter A., and Frank A. Gesek.
Department of Pharmacology and Toxicology, Dartmouth Medical School,
Hanover, New Hampshire.
APStracts 2:0003P, 1995.
ABSTRACT
The kidneys play a vital role in mineral homeostasis. In this review, the
handling of calcium and the methods currently applied to measuring its
intracellular concentration are discussed. The bulk of calcium absorption
proceeds in proximal tubules, with smaller fractions recovered by thick
ascending limbs, distal convulted tubules, and connecting tubules. Hormonally
regulated transcellular calcium absorption is essentially limited to distal
convoluted and conecting tubules. At physiological concentrations,
parathyroid hormone, calcitonin, and vitamin D increase net calcium
absorption. Calcium absorption by polarized epithelial cells is a two-step
process wherein calcium enters the cell across apical plasma membranes and
exits across basolateral membranes. Recent electrophysiological and
pharmacological experiments demonstrate that apical entry is mediated by
calcium channels, which are modestly calcium selective, sensitive to
dihydropyridine-type calcium channel blockers, and exhibit a wide range of
single-channel conductances. Cellular calcium efflux is mediated by Ca2+
ATPase and by Na+/Ca2+ exchange. Ca2+-ATPase activity is highest in segments
that exhibit significant rates of active calcium absorption. Multiple plasma
membrane Ca2+- ATPase isoforms have been identified in the kidney. Several
renal Na+/Ca2 exchange isoforms have been identified, and their role in
effecting calcium efflux is under investigation.
APS Manuscript Number P-0001-5.
Article publication scheduled July 1995 Physiological Reviews.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 16 May 1995.