Abstract
Callipeltin A is a cyclic depsidecapeptide isolated from the marine sponges Callipelta sp. and Latrunculia sp. that has been previously shown to increase the force of contraction of guinea-pig atria through the inhibition of Na +/Ca 2+ exchanger (NCX). We investigated the effect of callipeltin A on guinea-pig aortic rings contracted by procedures that activate NCX in “calcium entry mode”. Callipeltin A did not inhibit these contractions. Resting aorta responded to callipeltin A with a remarkable contraction that was concentration-dependent (EC50 0.44 μM). This contraction was not inhibited by the calcium channel blocker verapamil and was not mediated by the activation of alpha-adrenergic or endothelin-1 receptors. Pre-incubation of aortic rings with 0.5 mM amiloride, an inhibitor of NCX, completely prevented callipeltin A-induced contraction. Furthermore, callipeltin A (EC50 0.51 μM) increased Na + efflux of Na-loaded erythrocytes. 1 H and 13 C NMR resonances of callipeltin A revealed small but significant changes in the titration with K + and Na + salts. It is suggested that the effect of callipeltin A on cardiac and vascular preparations is linked to a Na-ionophore action.
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