The effect of potassium concentration on Ca45 uptake in frog sartorius muscle

Abstract

AbstractRadiocalcium uptake by frog sartorius muscle is increased as the potassium concentration of the bathing Ringer is increased from 1.6 mM to 32.0 mM; at higher concentrations of K+ no further increase in radiocalcium uptake occurs. Substitution of the chloride of Ringer solution by nitrate increases the amount of radiocalcium uptake at potassium concentrations between 1.6 and 32.0 mM but not at higher concentrations. The nitrate anion enhances both the maximum tension and the area of the contracture curves that occur between 16 and 80 mM K+. Comparison of paired muscle preparations in nitrate Ringer at 32 mM K+ and 80 mM K+ shows no difference in total radiocalcium uptake and no difference in the area under the contracture curves. When a three minute prequilibration period in Ca45 is omitted, the radiocalcium uptake by the sartorius muscle in 80 mM K+, Ca45 Ringer nitrate is reduced by 50% as compared to its mated muscle soaked in 32 mM K+, Ca45 Ringer nitrate. Within the limitations of the experimental techniques employed, it appears that calcium uptake is more prolonged at lower levels of potassium (32.0 mM) but the total amount taken up is the same as at higher levels of potassium (80 mM).