Melatonin reduces ³H-nitrendipine binding in the heart

The effect of melatonin on cardiac and brain voltage-sensitive calcium channels, as measured by ³H-nitrendipine binding, was examined in rats 3 hr after melatonin administration (either 0.5 or 1.0 mg/kg given subcutaneously). Scatchard analysis of the data on specific binding of ³H- nitrendipine with crude cardiac membranes from melatonin treated rats revealed significant decreases (P < 0.05 and P < 0.01 for the 0.5 and 1.0 mg/kg melatonin doses, respectively) in the density of Ca²⁺ channels without a change in their affinity for the ligand. At doses of 0.5 and 1.0 mg/kg of melatonin, B(max) values were 157 and 142 fmoles/mg protein, respectively, compared with a control value of 199 fmoles/mg protein in crude cardiac membranes. In brain, melatonin treatment did not statistically significantly influence either ³H-nitrendipine binding or its affinity when compared with control animals. These results suggest that melatonin modulates the functional status of voltage sensitive calcium channels in the heart, changes that may have implications for normal cardiac physiology and for the pharmacological manipulation of the heart.