Cytoplasmic pH dependency of Na+/H+ exchange in human platelets activated with thrombin, arachidonic acid, A23187 and TPA.
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.
Ogawa
A
A
Japanese Red Cross Central Blood Center, Tokyo.
Ishikawa
Y
Y
Sasakawa
S
S
D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D002352:Carrier Proteins / Q000097:blood*; D003593:Cytoplasm / Q000378:metabolism; D006801:Humans; D006859:Hydrogen / Q000097:blood*; D006863:Hydrogen-Ion Concentration; D009550:Nigericin / Q000494:pharmacology; D012964:Sodium / Q000097:blood*; D017923:Sodium-Hydrogen Exchangers; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013917:Thrombin / Q000502:physiology
D001095:Arachidonic Acids; D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D016718:Arachidonic Acid; D000001:Calcimycin; D006859:Hydrogen; D012964:Sodium; D013917:Thrombin; D013755:Tetradecanoylphorbol Acetate; D009550:Nigericin