VANADATE INCREASES CYTOSOLIC-FREE CALCIUM IN RAT AORTIC SMOOTH-MUSCLECELLS

Although several studies have shown that vanadate evokes vasoconstrict ion whether it elevates cytosolic free calcium, [Ca2+](i), in vascular smooth muscle (VSM) cells has not been investigated. The present stud y shows that acute additions of low concentrations of vanadate (10-200 mu M) to cultured aortic smooth muscle cells (ASMC) produced a rapid and a concentration-dependent increase in [Ca2+](i) with an EC(50) (me an +/- SEM) value of 42 +/- 11 mu M. Inclusion of vanadate (200 mu M) led to a significant increase (p < 0.05) in the peak [Ca2+](i) level t o 190 +/- 23 nM from a basal level of 102 +/- 2 nM. At concentrations > 200 mu M, vanadate caused quenching of fura-2 fluorescence. For exam ple, addition of 1 mM vanadate led to an apparent decrease in fluoresc ence by about 50 % (due to a quenching effect), followed by a transien t rise. H2O2, which is used in the preparation of peroxide forms of va nadate, pervanadate (PV), also produced a rise in [Ca2+](i). These dat a suggest that vanadate promotes vascular tone by elevating [Ca2+](i) in ASMC. However, [Ca2+](i) measurements made with higher concentratio ns of vanadate and PV, using the fura-2 method, must be interpreted wi th caution.