pH measurement in human skeletal muscle samples: effect of phosphagen hydrolysis

Measurements of muscle pH (pHm) with the homogenate technique are routinely made when extensive phosphagen hydrolysis has occurred. Upon exposure of the homogenate to 37 degrees C in the pH meter, phosphocreatine and ATP were rapidly degraded to 35 and 60% of control concentrations after 30 s. Attempts at chemically arresting this hydrolysis were unsuccessful. Therefore we examined the significance of phosphagen hydrolysis on pHm measurement in human biopsies taken at rest and following intense electrical stimulation. To accomplish this, pHm was measured at 0 degree C, where extensive hydrolysis did not occur. On the same homogenate, pHm was measured at 0 degree C with phosphagens and at 0 and 37 degrees C after phosphagen hydrolysis. The effect of phosphagen hydrolysis on pHm at 0 degrees C was used to estimate this effect at 37 degrees C. In resting samples, phosphagen hydrolysis produced a nonsignificant acidification of 0.008 pH units and, in electrically stimulated samples, a nonsignificant alkalinization of 0.033 units. Measurements of homogenate PCO2 suggested that most of the CO2 remained in the sample during pHm measurement at 37 degrees C. The present work substantiates the use of the homogenate technique as an accurate and practical method for the estimation of intracellular pH in resting and exercise human muscle samples.