AJP - Cell Physiology, Vol 235, Issue 3 122-C127, Copyright © 1978 by American Physiological Society
Cellular Cl content and concentration of amphibian skeletal and heart muscle
D. D. Macchia, P. I. Polimeni and E. Page
Toads (Bufo marinus) and frogs (Rana pipiens pipiens) were given
intraperitoneal injections of Na36Cl and Na235SO4. After in vivo
equilibration for 20--180 min, the animals were pithed, and their
ventricular and semitendinosus muscles were excised. Measurements of total
Cl (by titrimetry) and 36Cl (by radioassay) showed that specific
radioactivities of plasma and mus les approached equality within 1 h after
injection for toad skeletal and heart muscle and frog ventricles,
indicating complete exchange of cellular Cl with 36Cl. From the
simultaneously measured muscle water contents and 35SO4 spaces,
intracellular Cl concentrations in vivo (in mumol/g cell water) for
semitendinosus and ventricular muscles were calculated to be, respectively,
1.4 +/- 0.3 and 2.3 +/- 0.8 for Bufo and 1.7 +/- 0.7 and 4.8 +/- 2.4 for
Rana. In view of these low values, active cellular Cl accumulation seems
improbable, but cannot be rigorously excluded without simultaneous membrane
potential and intracellular ion activity measurements. A high concentration
of Cl in the sarcoplasmic reticulum of skeletal muscle is also inconsistent
with these measurements.
