Temperature dependence of nifedipine action

Recently, the use of calcium antagonists has been proposed as a new cardioplegic principle. At high doses (e.g. 10(-6)M nifedipine [3]) these drugs can be used for induction of reversible cardiac arrest. Apart from their effect on coronary flow, calcium antagonists seem to be beneficial to ischemic tissue because of their negative inotropic effect at high doses [6, 9]. Ionic cardioplegic solutions are commonly used in an advantageous combination with hypothermia. In the case of calcium antagonists, there is an indication that the specific cardioprotective effect is lessened at low temperatures [3]. Nifedipine is known to reduce contraction force without abolishing the generation of action potentials even at excessive doses [2]. To quantify the suppressing effect of nifedipine on the generation of contractions, we determined the maximal possible contraction frequency (Fm) under electrical stimulation at different temperatures. In isolated myocardial cells, Fm can be determined from the cell contour movements even with an almost complete force reduction and therefore it represents a measure for effective contractile refractoriness.