Effect of isosmotic removal of extracellular Ca2+ and of membrane potential on cell volume in muscle cells
Peña-Rasgado, C.; McGruder, K.D.; Summers, J.C.; Rasgado-Flores, H.
American Journal of Physiology 267(3 Pt 1): C768-C775
1994
ISSN/ISBN: 0002-9513 PMID: 7943206 Document Number: 429768
Isosmotic removal of extracellular Ca-2+ (Ca,) and changes in membrane potential (V-m) are frequently performed manipulations. Using isolated voltage-clamped barnacle muscle cells, we studied the effect of these manipulations on isosmotic cell volume. Replacing Ca-o by Mg-2+ induced 1) verapamil-sensitive extracellular Na+-dependent membrane depolarization, 2) membrane depolarization-dependent cell volume reduction in cells whose sarcoplasmic reticulum (SR) was presumably loaded with Ca-2+ (intracellular Ca-2+ (Ca-i)-loaded cells), and 3) cell volume increase in cells whose SR was presumably depleted of Ca-2+ (Ca-i-depleted cells) or in Ca-i-loaded cells whose V-m was held constant. Membrane depolarization induced 1) volume reduction in Ca-i-loaded cells or 2) verapamil-sensitive volume increase in Ca-i-depleted cells. This suggests that, in Ca-i-loaded cells, membrane depolarization induces SR Ca-2+ release, which in turn promotes volume reduction. Conversely, in Ca-i-depleted cells, the depolarization activates Na+ influx through a verapamil-sensitive pathway leading to the volume increase. This pathway is also revealed when Ca-o is removed in either Ca-i-depleted cells or in cells whose V-m is held constant.