Changes in intracellular pH and inorganic phosphate concentration during and after muscle contraction as studied by time-resolved 31P-NMR. Alkalinization by contraction.

The changes in intracellular pH and concentration of inorganic phosphate (Pi) were studied during and after contraction of bullfrog sartorius muscles by using 31P-NMR. The intracellular pH was 7.04 in resting muscles at 4 degrees C and an alkalinization by as much as 0.08 pH unit occurred following 5 s tetanic contraction. During the recovery period after contraction the increased level of intracellular pH returned to the resting level, the time course of which coincided with that of the recovery of the Pi concentration. Based on the changes in the intracellular pH and Pi concentration, the buffering power was estimated to be 18 mM/pH unit.