Identification of a sodium-bicarbonate symport in human platelets

Oscar A. Gende, Horacio E. Cingolani

Research output: Contribution to journalArticlepeer-review

Abstract

Intracellular pH (pH(i)) was measured in human platelets using fluorescent probes. Basal pH(i) was higher in HCO3--buffered solutions (7.33 ± 0.01) than in nominally HCO3- free, Hepes-buffered solutions (7.16 ± 0.01, P < 0.05). Addition of EIPA caused a fall in Hepes, but did not inhibit the increase of pH(i) when platelets maintained in Hepes were transferred to a CO2/HCO3- buffer. After an intracellular acidosis induced by an NH4Cl prepulse, the initial velocity of recovery (d(pH)/dt(i), in pH units/min) was 3.32 ± 0.69 in Hepes-buffered solution and 2.85 ± 0.88 in HCO3- media. Taking into account the differences in buffer capacity, the efflux of acid equivalents after 1.2 min was twice as much in the presence of bicarbonate. The addition of 30 μmol/l EIPA effectively blocked acid efflux (d(pH)/dt(i) = 0.08 ± 0.03) in a nominally HCO3- -free solution, whereas the recovery was reduced but not abolished (d(pH)/dt(i) = 0.37 ± 0.10, P < 0.05) in the presence of bicarbonate. The stilbene derivative SITS further inhibited the ETPA-resistant pH(i) recovery. Removal of external Na+ inhibited the HCO3- -dependent recovery whereas depletion of internal Cl-, did not suppress it. Depolarization of the membrane had no effect on this recovery. The results suggest the contribution of an electroneutral Na+/HCO3- cotransport in the recovery of pH(i) following an acid load. Both the Na+/H+ antiport and the HCO3--dependent mechanism contribute approx. 50% each to the total acid equivalent efflux during the recovery from a pH(i) 6.46 ± 0.14 to the basal pH(i) in human platelets.

Original languageEnglish (US)
Pages (from-to)119-124
Number of pages6
JournalBiochimica et Biophysica Acta - Biomembranes
Volume1278
Issue number1
DOIs
StatePublished - Jan 12 1996

Keywords

  • Bicarbonate cotransport
  • Intracellular
  • Platelet
  • Sodium ion
  • pH
  • pH(i) regulation

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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