MELATONIN REDUCES H-3 NITRENDIPINE BINDING IN THE HEART

The effect of melatonin on cardiac and brain voltage-sensitive calcium channels, as measured by H-3-nitrendipine binding, was examined in ra ts 3 hr after melatonin administration (either 0.5 or 1.0 mg/kg given subcutaneously). Scatchard analysis of the data on specific binding of H-3-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+ c hannels 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 d id not statistically significantly influence either H-3-nitrendipine b inding or its affinity when compared with control animals. These resul ts suggest that melatonin modulates the functional status of voltage s ensitive calcium channels in the heart, changes that may have implicat ions for normal cardiac physiology and for the pharmacological manipul ation of the heart.