Leakage of the fluorescent Ca2+ indicator fura-2 in smooth muscle.
The movement of a fluorescent intracellular Ca2+ indicator, fura-2, in smooth muscle was examined. Strips of rat and rabbit aortas and bovine trachea were loaded with the acetoxymethyl ester of fura-2 (fura-2/AM), followed by washing with normal physiological solution. Not only fura-2/AM but also fura-2 was detected in the washout solution. The amount of fura-2 in the cells, measured fluorometrically, decreased gradually during the washout. The decrease was fastest in rat aorta followed by rabbit aorta > bovine trachea. In rat aorta, fura-2 leakage was inhibited by an inhibitor of anion transport, probenecid, or by a decrease in bath temperature. The Ca2+ ionophore ionomycin (10 microM) increased the leakage of fura-2, which was not inhibited by probenecid, possibly because a high concentration of ionomycin nonselectively increased membrane permeability. These results suggest that fura-2/AM is cleaved to fura-2 in the cell which gradually leaked out of the cell mainly by an anion transport system. The amount of fura-2 in the cell seemed to be determined mainly by the rate of leakage of fura-2, which is the largest in rat aorta followed by rabbit aorta and bovine trachea.
Mitsui
M
M
Department of Veterinary Pharmacology, Faculty of Agriculture, University of Tokyo, Japan.
Abe
A
A
Tajimi
M
M
Karaki
H
H
D000818:Animals; D001013:Aorta, Thoracic / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D016257:Fura-2 / Q000031:analogs & derivatives / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D009130:Muscle, Smooth / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar; D014132:Trachea / Q000378:metabolism
C049925:fura-2-am; D002118:Calcium; D016257:Fura-2