The effect of [Na+]i and [Na+]o on Ca2+ mobilization in the rat aortic smooth muscle cell line A7r5.
Measurements of intracellular calcium (Ca2+i) and sodium (Na+i) have been made in single smooth muscle cells in confluent cultures of the A7r5 cell line using the Ca(2+)- and Na(+)-sensitive dyes Fura-2 and sodium-binding benzofuran isophthalate (SBFI). Reversal of the Na+ gradient in control cells results in a small increase in Ca2+i and slows the rate of recovery in Ca2+i following agonist stimulation. This suggests that a Na(+)-Ca2+ exchange mechanism may be functioning in these cells. In ouabain-pretreated cells, Na+i is elevated and the recovery from agonist stimulation is significantly slowed. This suggests that the elevation of Na+i alters Ca2+ homeostasis. Reversal of the Na+ gradient in ouabain-pretreated cells results in a transient increase in Ca2+i which was larger than in control cells. This response is reduced during a second or third exposure to zero Na+o.NA+i, in Na(+)-loaded cells, falls in the absence of external Na+. This fall is slowed in the absence of external Ca2+ supporting the idea that the Na+ loss is via Na(+)-Ca2+ exchange. The possible modulation of the Na(+)-Ca2+ exchanger and Ca2+ mobilization 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; D001011:Aorta / Q000378:metabolism*; D001127:Arginine Vasopressin / Q000494:pharmacology; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D007474:Ion Exchange; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D009994:Osmolar Concentration; D051381:Rats; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology*
D001127:Arginine Vasopressin; D012964:Sodium; D002118:Calcium