Evidence for Na(+)-Ca2+ exchange and Ca(2+)-induced Ca2+ release in a cultured vascular smooth muscle cell line from the rat.
Measurements of intracellular calcium (Cai2+) and sodium (Nai+) have been made in single smooth muscle cells from the rat aortic cell line (A10) using the Ca(2+)- and Na(+)-sensitive dyes Fura-2 and SBFI (sodium-binding benzofuran isophthalate). The effects of manipulation of intracellular and extracellular Na+ on Cai2+ have been investigated. Reversal of the Na+ gradient in control cells does not result in any measurable increase in Cai2+ or change in the rate of recovery of the cells from agonist stimulation, suggesting that there is little functional Na(+)-Ca2+ exchange. In ouabain-pre-treated cells however, the recovery from agonist stimulation is significantly slowed, suggesting that in the presence of an elevated intracellular Na+ concentration there is an alteration in the Ca(2+)-handling mechanisms. Reversal of the Na+ gradient in ouabain-pre-treated cells results in a transient increase in Cai2+ followed by a slow secondary rise. The transient component of this rise is absent on a second activation of the cell or by prior mobilization of the intracellular stores of Ca2+ by agonist. Data presented in this paper suggest the possibility that the transient component is due to a Ca(2+)-induced Ca(2+)-release mechanism triggered by an initial influx of Ca2+. The mechanism underlying this influx is not known but may involve the Na(+)-Ca2+ exchanger operating in reverse. The possible modulation of the Na(+)-Ca2+ exchanger and Ca(2+)-induced Ca2+ release by internal Na+ is discussed.
Gillespie
J I
JI
Department of Physiological Sciences, Medical School, The University, Newcastle upon Tyne.
Otun
H
H
Greenwell
J R
JR
Dunlop
W
W
D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D007474:Ion Exchange; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger
D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; D001127:Arginine Vasopressin; D010042:Ouabain; D012964:Sodium; D002118:Calcium