Presence of Na+/Ca2+ exchange activity and its role in regulation of intracellular calcium concentration in bovine adrenal chromaffin cells.
The presence of a Na+/Ca2+ exchanger in bovine adrenal chromaffin cells was demonstrated by measuring the efflux of 45Ca2+ which had been preloaded into cells by a brief depolarization. The efflux of 45Ca2+ was dependent on extracellular Na+ (Na+o); 45Ca2+ efflux was significantly decreased by replacing Na+o with N-methylglucamine (NMG), or Li+. Replacement of Na+o by NMG increased the resting intracellular Ca2+ concentration ([Ca2+]i) of freshly isolated chromaffin cells. This could be reversed by adding Na+, suggesting that Na+/Ca2+ exchanger activity was involved in maintaining [Ca2+]i at its resting level. The initial rate of Na(+)-dependent [Ca2+]i recovery after Ca2+ loading by depolarization was dependent on the level of [Ca2+]i. There was an apparent linear relationship between the activity of the Na+/Ca2+ exchanger and [Ca2+]i both in the presence and absence of Na+o. When cells were treated with other stimuli, including 10 microM DMPP or 40 mM caffeine, the ability of the stimulated cells to decrease [Ca2+]i was significantly reduced upon replacing Na+o with NMG. Our data show that the Na+/Ca2+ exchanger is one of the major pathways for regulating [Ca2+]i in chromaffin cells in both resting and stimulated states.
Chern
Y J
YJ
Institute of Biomedical Sciences, Academia Sinica, Nankang, Taipei, Taiwan, Republic of China.
Chueh
S H
SH
Lin
Y J
YJ
Ho
C M
CM
Kao
L S
LS
D000313:Adrenal Medulla / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D004246:Dimethylphenylpiperazinium Iodide / Q000494:pharmacology; D066298:In Vitro Techniques; D007474:Ion Exchange; D007700:Kinetics; D012964:Sodium / Q000378:metabolism*
D002110:Caffeine; D004246:Dimethylphenylpiperazinium Iodide; D012964:Sodium; D002118:Calcium