EFFECTS OF CALCIUM, STRONTIUM, AND BARIUM ON ISOLATED PHRENIC NERVE-DIAPHRAGM PREPARATION OF RAT AND THEIR INTERACTIONS WITH DILTIAZEM AND NIFEDIPINE

Abstract : Abstract : Abstract : Abstract : Calcium (Ca 2+ ), strontium (Sr 2+ ), and barium (Ba 2+ ) are expected to exert similar chemical and pharmacological effects. The effects of barium, strontium and calcium were studied on the contractions of rat phrenic nerve-diaphragm preparations, following electrical stimulation and their interactions with nifedipine (nif) and diltiazem (DZM) were also studied. Low doses of strontium chloride (SrCl 2 ), barium chloride (BaCl 2 ) and calcium chloride (CaCl 2 ) were able to increase the force of contraction of the rat diaphragm when actively stimulated. Diltiazem inhibited the stimulant effects of Sr2+, Ba2+, and Ca2+. On the other hand, nifedipine blocked the effects of Sr 2+ and Ca 2+ but potentiated the effects of Ba 2+ . Strontium, barium, and calcium restored the contractility of the muscle following electrical stimulation when the tissue was in biological fluid absolutely depleted of calcium. These findings suggest that Sr 2+ and Ba 2+ may be able to substitute Ca2+ in the rat diaphragm for its contractions and nifedipine and diltiazem may follow different mechanisms of actions or channels in their blocking effects.