Effects of calcium, strontium, and barium on isolated phrenic nerve-diaphragm preparation of rat and their interactions with diltiazem and nifedipine.

ABSTRACT

Calcium (Ca2+), strontium (Sr2+), and barium (Ba2+) 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 (SrCl2), barium chloride (BaCl2) and calcium chloride (CaCl2) 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 Sr2+ and Ca2+ but potentiated the effects of Ba2+. 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 Sr2+ and Ba2+ 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.