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Cytoplasmic pH dependency of Na+/H+ exchange in human platelets activated with thrombin, arachidonic acid, A23187 and
A Ogawa1, Y Ishikawa, S Sasakawa
1Japanese Red Cross Central Blood Center, Tokyo.
Abstract:
The cytoplasmic pH (pHc) of human platelets was lowered to 6.8-7.2 by treatment with various doses of nigericin (K+/H+ ionophore), then these platelets were stimulated with thrombin, arachidonic acid (AA), A23187 or 12-o-tetradecanoylphorbol-13-acetate (TPA), to monitor the pHc changes using a pH-sensitive fluorescent dye, BCECF. The pHc increased with the stimulation in an amiloride-sensitive manner only when the resting-pHc was lower than a certain value (pHc 6.99 for thrombin-stimulation, 6.95 for AA, 7.04 for A23187 and 6.95 for TPA, n = 3). At a higher resting-pHc, the pHc decreased. Similar observations were found using platelets acid-loaded by Na-acetate treatment. These results suggest that stimulation-induced activation of the Na+/H+ exchanger depends on cytoplasmic H+ concentration, and it can function properly only when the resting-pHc is lower than about pHc 7.