Regulation of intracellular calcium in N1E-115 neuroblastoma cells: the role of Na /Ca exchange

Kopper, Kara L., and Joseph S. Adorante. Regulation of intracellular calcium in N1E-115 neuroblastoma cells: the role of Na /Ca2 exchange. Am J Physiol Cell Physiol 282: C1000–C1008, 2002; 10.1152/ajpcell.00182.2001.—In fura 2-loaded N1E-115 cells, regulation of intracellular Ca2 concentration ([Ca2 ]i) following a Ca2 load induced by 1 M thapsigargin and 10 M carbonylcyanide p-trifluoromethyoxyphenylhydrazone (FCCP) was Na dependent and inhibited by 5 mM Ni2 . In cells with normal intracellular Na concentration ([Na ]i), removal of bath Na , which should result in reversal of Na /Ca2 exchange, did not increase [Ca2 ]i unless cell Ca2 buffer capacity was reduced. When N1E-115 cells were Na loaded using 100 M veratridine and 4 g/ml scorpion venom, the rate of the reverse mode of the Na /Ca2 exchanger was apparently enhanced, since an 4to 6-fold increase in [Ca2 ]i occurred despite normal cell Ca2 buffering. In SBFI-loaded cells, we were able to demonstrate forward operation of the Na /Ca2 exchanger (net efflux of Ca2 ) by observing increases ( 6 mM) in [Na ]i. These Ni2 (5 mM)-inhibited increases in [Na ]i could only be observed when a continuous ionomycininduced influx of Ca2 occurred. The voltage-sensitive dye bis-(1,3-diethylthiobarbituric acid) trimethine oxonol was used to measure changes in membrane potential. Ionomycin (1 M) depolarized N1E-115 cells ( 25 mV). This depolarization was Na dependent and blocked by 5 mM Ni2 and 250–500 M benzamil. These data provide evidence for the presence of an electrogenic Na /Ca2 exchanger that is capable of regulating [Ca2 ]i after release of Ca2 from cell stores.