Calcium Equilibrium in Muscle

Abstract

1. A study of the calcium equilibrium in isolated frog muscle has been attempted. 2. When sartorius muscles were immersed in Ca45 Ringer's solution, the surface phase took up the Ca45 in about 1 minute; the extracellular water space and connective tissue in about 30 minutes; and the intracellular space in about 300 minutes. 3. The percentages of total calcium in the whole muscle immersed in Ringer's solution was as follows: 10 per cent in the surface phase; 12 per cent in the extracellular water space; 17 per cent in the dry connective tissue; 24 per cent in the intracellular space; and 37 per cent as non-exchangeable calcium. 4. The exchange constants of isolated frog sartorius muscle to calcium has been determined. The flux of intracellular calcium in the steady state was approximately 0.8 mM/(liter hr). 5. It appears that there is a calcium pump pushing calcium out of the cell against an electrochemical gradient of about 4 cal./mM of calcium. However, since the flux is low, the maximum energy required per hour to pump calcium out of the cell against this high gradient is only about 2 cal./kg. muscle or about 1 per cent of the resting energy.

Calcium Influx in Skeletal Muscle at Rest, During Activity, and During Potassium Contracture

“…0.015 of those for net sodium entry (see pages 216 and 217 in reference 32); even if the sodium content of whole muscle were doubled by activity--representing an increment of 20 #g/gin. in cat muscle (4)--this would correspond to a calcium uptake of 0.3 #5, or about 30 per cent or less than that found in mammalian and amphibian muscle (5,8,9).…”

Autoradiographic Studies of Intracellular Calcium in Frog Skeletal Muscle

“…From kinetic studies with frog sartorius, Shanes and Bianchi (6) and Gilbert and Fenn (21) have divided the muscle calcium into several components, extracellular fluid, connective tissue-bound, rapidly exchanging cellular (presumably bound to the cell surface), slowly exchanging'cellular (presumably intracellular), and inexchangeable. The half-times of exchange or the two cellular components, 10 minutes and 300 to 500 minutes, are similar to those found in the toe muscle.…”

Calcium Flux and Contractility in Guinea Pig Atria

“…As in earlier calcium studies (39), the calcium of the guinea pig atrium has been divided into three different components by the kinetics of Ca 4~ washout: (a) rapidly exchangeable; (b) slowly exchangeable; and (c) non-exchangeable. In addition to calcium in the extracellular fluid and probably calcium bound to connective tissue, it is not unlikely that the rapidly exchanging fraction includes some calcium loosely bound to the cell surface.…”