MYOPLASMIC FIXED CHARGES OF THE BARNACLE MUSCLE-FIBER

The experimental model used to study diffusion and electrical conduction in the cytoplasm of large muscle fibers was adapted to evaluate the myoplasmic density of fixed charges. Membranes of myoplasm were prepared and øX, the myoplasmic thermodynamically effective charge density, was calculated from the membrane potential (Kamo, N., Toyoshima, Y. and Kobatake, Y. (1971) Kolloid Z.u.Z. Polymère 1061-1068) when these membranes were used as the partition between two electrolyte solutions. The dilution of KCl in the external solutions reduced øX, which increases with the reduction of the water content in the membrane of myoplasm. With a water content of 73.0 ml/100g KCl concentration in the external medium equal to 0.15 M, øX was evaluated to 0.058 equiv/l. The substitution of KCl by NaCl introduces a reduction in øX of 20-50% depending on [KCl] in the external solutions. The addition of ATP, Mg2+ and Ca2+ also causes a reduction of øX by 30-50% according to the experimental conditions. These results indicate that the fraction of counterions dissociated from the myoplasmic macromolecules is reduced when the concentration of the counterions is diminished or when KCl is replaced by NaCl. It also suggests a reduction of øX during muscular contraction. © 1979.