Rat vascular smooth muscle cells in culture contract upon Ca2+ repletion after depletion

We investigated the effects of Ca2+-repletion following depletion on cultured vascular smooth muscle cells (SMCs) from the rat aorta. With Ca2+-repletion, the cells in primary cultures contracted, as indicated by a decrease in cell area. The process was slow (30 min to maximum effect) and reversible (relaxation completed by 120 min). Contraction during Ca2+-repletion was never observed in subcultured cells. The SMCs in primary culture after treatment maintained the ability to grow and to exclude dye, with a normal plating efficiency. There was no treatment-related additional leakage of intracellular enzymes, LDH and CPK, into the medium. Ca2+-repletion at first accelerated the 45Ca uptake by SMCs (1-5 min after repletion) and then increased Ca2+ efflux after about 10 min of Ca2+-repletion. We conclude that Ca2+-repletion after depletion induces a transient and reversible contraction of vascular SMCs in primary culture, without cell injury and in association with a transient increase in Ca2+ influx and then efflux. This phenomenon may relate to the decrease in perfusion flow in hearts and kidneys during Ca2+-repletion after depletion (Ca2+-paradox).