Na(+)- and Ca(2+)-dependent pH regulation in unstimulated human platelets.
The influence of transmembrane Na+ and Ca2+ gradients on cytosolic pH (pHi) and free Ca2+ concentration ([Ca2+]i) have been examined in unstimulated human platelets with the aid of BCECF and Fura-2 fluorescent dyes. The removal of external Na+ (Na+o) acidified the cytosol in a pHo-dependent manner which was insensitive to EIPA and DIDS, the inhibitors of the Na+/H+ exchanger and bicarbonate transporters. Na+o removal also increased [Ca2+]i by 17 +/- 5%, but the amplitude of the concomitant acidification was independent on Ca2+ influx or cytosolic Ca2+ concentration. In contrast, in the presence of 145mM Na+o, a rise in external Ca2+ concentration from 1 to 2mM increased [Ca2+]i by 38 +/- 11% and acidified the cytosol by 0.16 +/- 0.04 pH units. These results indicated that, in resting human platelets, the transmembrane Na+ gradient is a major determinant of pHi. Two Na(+)-dependent processes have been found: one is triggered by an external acidification and the other activated by a rise in Ca2+ influx or cytosolic concentration.
Astarie
C
C
Department of Pharmacology, CNRS SDI 6167, Necker Medical School, Paris, France.
David-Dufilho
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M
Devynck
M A
MA
D001792:Blood Platelets / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D012964:Sodium / Q000502:physiology*
D012964:Sodium; D002118:Calcium