Dihydropyridine Ca++ channel agonists enhance 45Ca++ uptake by rabbit aortic smooth muscle cells (RASMC) at 15-50 mM K+. Nifedipine and D-600 inhibit such effects

RASMC were prepared, subcultured to passage number22 and characterized morphologically and for 45Ca++ uptake. The initial rate of 45Ca++ uptake in 50 mM K+ was three times the rate in 5 mM K+. Steady state 45Ca++ uptake increased with K+ concentration in a dose-dependent manner. Threshold was at approx. 15 mM K+. At 25-50 mM K+ the maximum K+-induced Ca++ uptake was 1.3 nmol Ca++/mg protein or 0.6 nmol Ca++/106 cells. The three dihydropyridine agonists (+/-) Bay K 8644, (+/-) CGP 28392 and (+) 202-791 enhanced the 45Ca++ uptake at K+ greater than or equal to 15 nM. At the 45Ca++ uptake threshold of 15 mM each agonist potentiated 45Ca++ uptake in a dose-dependent manner. Responses were antagonized competitively by nife-dipine and non-competitively by (+/-) D-600. The (-) 202-791 inhibited K+-induced 45Ca++ uptake (IC50 = 4.0 x 10-9 M). Based on the agreement with literature data on contraction, electrophysiological and 45Ca++ uptake studies using intact vascular tissues, it is concluded that the RASMC possess voltage-dependent Ca++ channels functionally similar to intact vascular muscle. These cells are a suitable model system for pharmacological studies of Ca++ channels and for characterization of Ca++ channel modulators