Measurement of the intracellular pH of blood platelets using a photolabel fluorescent probe.

The internal pH of blood platelets using the intracellular photolabel probe azidofluorescein diacetate was determined. No change of intracellular pH during thrombin activation of human platelets was observed. Platelets were found to adjust themselves very quickly to the external pH. Quantitative subcellular localization of the attachment sites of this probe reveals that most of it is bound to low molecular weight proteins or peptides.