AJP - Cell Physiology, Vol 248, Issue 5 436-C441, Copyright © 1985 by American Physiological Society
Cultured rat vascular smooth muscle cells: extracellular calcium and Na+-K+ regulation
M. Kino, A. Tokushige, H. Tamura, L. Hopp, B. M. Searle, F. Khalil and A. Aviv
This study explores the relationship between extracellular calcium (Cao)
and Na+-K+ regulation as it particularly pertains to the activity of the
Na+ pump in cultured vascular smooth muscle cells (VSMCs) originating from
Sprague-Dawley rats. As compared with cells incubated in media containing
0.5, 2.0, or 4.0 mM calcium, when the Na pump is active, VSMCs incubated in
a Ca-deficient medium show a marked increase in intracellular sodium and no
significant change in intracellular potassium. Associated with the rise in
intracellular sodium there is an augmented activity of the Na pump. When
the Na pump is inhibited, VSMCs incubated in either high-Ca medium (Cao =
4.0 mM) or Ca-deficient medium manifest a greater decline in intracellular
potassium than cells incubated in media containing 0.5 or 2.0 mM calcium.
Furthermore, when the Na pump is inhibited, VSMCs incubated in a
Ca-deficient medium exhibit higher intracellular sodium levels in
comparison with their counterparts incubated in media containing calcium.
Flux experiments indicate that the aforementioned changes reflect increased
membrane permeabilities to Na+ and K+. It is concluded that by regulating
the permeability of the VSMC membrane, Cao plays an important role in the
intracellular Na+-K+ homeostasis and that its effect on the Na pump is
mediated via perturbations in the intracellular Na+ and K+ concentrations.
