Abstract
NP-252, a new dihydropyridine derivative, and nifedipine non-competitively inhibited contractile responses to KCl and responses to Ca 2+ in Ca 2+-free medium containing KCl in rabbit aorta and renal, mesenteric, coronary and basilar arteries, mesenteric veins and vena cava. The effects of NP-252 in these smaller arteries and veins were much greater than those in aorta. However, a similar differential selectivity was not seen with nifedipine. In aorta, only NP-252 reduced total La 3+ resistant 45Ca binding. However, the increases in bound 45Ca at La 3+ resistant sites and 45Ca unidirectional influx due to KCl were inhibited by both NP-252 and nifedipine. The displacement of [ 3H]nitrendipine binding to rabbit aorta was monophasic for both NP-252 and nifedipine. In guinea-pig papillary muscles, NP-252 (> 10 −7 M) slightly decreased action potential duration, developed tension and slow action potentials. The cardiac effects of NP-252 were much less prominent than those of nifedpine. These results indicate that NP-252 inhibits voltage-operated Ca 2+ channels in small arteries and veins much more effectively than those in aorta, and this tissue selectivity is more apparent for NP-252 than nifedipine.
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