Abstract

Stuclies have been made of a number of factors which might influence the amount of tension generated in glycerinated myocardial fibers by ATP. ATP concentrations from 5 x 10^-4M to 1 x 10-2M were about equally effective in generating similar degrees of tension. An increase of pH from 7.5 to 9.0 was associated with slight increase in generated tension. Calcium was not found to inhibit the generation of tension, and when sodium was time principal cation the amount of tension generated was only 5 per cent less than the tension generated when potassium was the principal cation. The tension generated was not significantly influenced by ionic strengths from 0.05 to 0.20. At ionic strengths of 0.25 and 0.30, tension was progressively diminished to 50 per cent of maximum. The significance of these results for various theories of how ions influence contraction are discussed.