AJP - Renal Physiology, Vol 249, Issue 3 346-F355, Copyright © 1985 by American Physiological Society
Effect of calcium on transport characteristics of cultured proximal renal cells
L. M. Sakhrani, N. Tessitore and S. G. Massry
We examined the effects of acute changes in extracellular and intracellular
calcium on transport processes in primary culture of proximal rabbit renal
cells. A change in extracellular calcium from 0 to 3 mM inhibited
amiloride-sensitive sodium uptake by 30%, and this effect was maximal at 1
mM calcium. Other polyvalent cations (Mn2+, Mg2+, La3+, and Ba2+) produced
quantitatively similar inhibition of amiloride-sensitive sodium uptake
compared with calcium. An increase in cytosolic calcium produced by calcium
loading (20 mM) or by A23187 (20 microM) resulted in an inhibition of
25-40% of amiloride-sensitive sodium uptake. Moreover, quinidine (10(-4)M)
and ruthenium red (3 microM), agents presumed to increase cytosolic
calcium, inhibited amiloride-sensitive sodium uptake by 20-60%. Both these
agents also inhibited sodium-dependent phosphate uptake by 20% but had no
effect on ouabain-sensitive 86Rb+ uptake or on sodium-dependent
alpha-methylglucoside uptake. Our data indicate that increases in
extracellular calcium inhibit amiloride-sensitive sodium uptake and
increases in cytosolic calcium inhibit sodium-dependent phosphate and
amiloride-sensitive sodium uptakes. The effect of extracellular calcium may
be due to charge screening and/or binding to the negatively charged plasma
membrane or due to alterations in membrane fluidity.
