AJP - Cell Physiology, Vol 234, Issue 3 110-C114, Copyright © 1978 by American Physiological Society
Association of increased pHi with calcium ion release in skeletal muscle
R. J. Connett
The pH difference across the cell membrane of frog sartorius muscle cells
was measured with the distribution of 5,5-dimethyl-2,4-oxazolidine-dione
(DMO) as the marker. Depolarization of the muscles to values at or below
the contraction threshold caused by elevating external potassium up to
approximately 20 mM resulted in an internal alkalinization. The change was
smaller with superthreshold depolarization (20--30 mM [K+]). The
alkalinization was blocked by agents that block calcium release from the
sarcoplasmic reticulum (procaine and dantrolene sodium). Other agents that
cause calcium release (caffeine, theophylline, and quinine) were found to
give alkalinization when tested at concentrations just below the
contracture threshold. Increased acidification of the extracellular medium
was associated with the internal alkalinization. The data were interpreted
as indicating the presence of a calcium-stimulated H+ and/or OH- ion
transport system in the muscle membrane.
