Inhibition of calcium entry preserves contractility of arterial smooth muscle in culture

The addition of the growth stimulator fetal calf serum (FCS, 10%) to rings of rat tail artery causes an increase in [Ca2+](i), accompanied by contraction. This response was inhibited by the calcium entry blocker verapamil (1 mu M). To investigate the effect of Ca2+ entry blockade on growth and contractility, rings of rat tail artery were cultured for 4 days in medium with or without FCS and then mounted for tension registration and stimulated with noradrenaline (NA) or high-K+ solution. In cultured rings growth was quantitated by [H-3]-thymidine incorporation and increase in protein contents. FCS in the medium stimulated DNA synthesis by about 2-fold and increased protein contents by about 70%. The growth-stimulated cultured rings developed less force than freshly prepared rings (2.2 +/- 0.3 vs. 8.3 +/- 1.0 mN/mm). The addition of 1 mu M verapamil to the medium during culture increased maximal NA-evoked force to 5.0 +/- 0.4 mN/mm but had no effect on the increases in DNA synthesis and protein contents. Force developed by growth-arrested rings, cultured in the absence of FCS, was not different from that of freshly prepared rings (7.2 +/- 0.6 mN/mm). Verapamil did not affect maximal force in these rings. Similar responses were seen when contraction was elicited by high-K+ solution. We conclude that verapamil, present during culture, preserves contractility of arterial smooth muscle, and that this effect is not parallel to inhibition of growth.