Na+/Ca2+ exchange-mediated calcium entry in human lymphocytes.
Regulation of cytosolic Ca2+ and cytosolic Na+ is critical for lymphocyte cation homeostasis and function. To examine the influence of cytosolic Na+ on Ca2+ regulation in human peripheral blood lymphocytes, Ca2+ entry and cytosolic Ca2+ (measured with fura-2) were monitored in cells in which cytosolic Na+ was increased and/or the Na+ gradient was decreased by reduction of external Na+ concentration. Ouabain-treated cells (0.1 mM for 30 min at 37 degrees C), suspended in Na(+)-free medium, showed a 30-65% increase in Ca2+ uptake compared to cells in 140 mM Na+ medium. Enhanced Ca2+ influx was entirely dependent on ouabain pretreatment and reversal of the Na+ gradient. Na pump inhibition or Na ionophore addition and subsequent exposure to Na(+)-free medium resulted in a sustained elevation of cytosolic Ca2+. As preincubation of cells in Ca(2+)-free medium further enhanced the ouabain-dependent increase in cytosolic Ca2+, the effects of the microsomal Ca(2+)-ATPase inhibitor thapsigargin on Ca2+ influx and cytosolic Ca2+ were studied. Thapsigargin stimulated Ca2+ entry following ouabain pretreatment and reversal of the Na+ gradient; the effects of thapsigargin were retained in the presence of LaCl3, a potent inhibitor of store-dependent calcium influx pathways. These results show lymphocytes demonstrate Na+/Ca2+ exchange activity and suggest the Na+/Ca2+ exchanger modulates cytosolic Ca2+ following intracellular Ca2+ store depletion.
Balasubramanyam
M
M
Hypertension Research Center, University of Medicine and Dentistry-New Jersey Medical School, Newark 07103.
Rohowsky-Kochan
C
C
Reeves
J P
JP
Gardner
J P
JP
D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000502:physiology*; D006801:Humans; D008214:Lymphocytes / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; D013729:Terpenes; D010042:Ouabain; D019284:Thapsigargin; D012964:Sodium; D002118:Calcium