Influence of temperature upon contractile activation and isometric force production in mechanically skinned muscle fibers of the frog

Abstract

Increasing temperature (4-22°C) increases the Ca2+ concentration required for activation of mechanically skinned frog muscle fibers. The pCa required for 50% maximal force (pCa50) was inversely proportional to absolute temperature. Assuming that relative force is directly related to fractional occupancy of the Ca2+-binding sites on troponin that regulate force, the shift was consistent with a Gibbs free energy change of binding (ΔG) of about -7.8 kcal/ mol. This is close to the ΔG for Ca2+ binding to the calcium-specific sites on troponin C reported by others. Decreasing Mg2+ from 1 mM to 60 µM shifts the force-pCa curves at either 4 or 22°C to higher pCa, but the shift of pCaso with temperature over this range (0.4 log units) was the same at low and high Mg2+. Maximal force increased with temperature for the entire range 4-22°C with a Q10 of 1.41, and over the restricted range 4-15°C with a Quo of 1.20. From the dual effects of temperature on Ca2+ activation and maximal force, one would expect that force would respond differently to temperature change at high or low Ca2+. At high Ca2+, a temperature increase will lead to an increased force. However, at low to intermediate Ca2+ levels (below the intersection of the forcepCa curves for the initial and final temperatures), steady state force should decrease with increasing temperature. The inverse responses should occur with a decrease in temperature. These responses are observed when temperature is changed by rapid solution exchange. © 1982, Rockefeller University Press., All rights reserved.