The intracellular pH of the human platelet.

A great number of cells are acidic compared to their environment (1). Changes in the pH of extracellular fluid are important primarily as they affect hydrogen ion activity within the cell. However, cellular hydrogen ion activity is dependent upon a number of factors, so that it is impossible to predict cellular pH from knowledge of extracellular pH alone (2, 3). Since the interior of most cells is not homogeneous, measurements of cellular pH reflect an aggregate hydrogen ion activity (1). The present studies were performed to determine the aggregate intracellular pH of the human platelet and to characterize changes in cellular pH subsequent to changes of pH in extracellular fluid.