Pineal methoxyindoles depress calcium uptake by rat brain synaptosomes

The effect of several pineal methoxyindoles on 45Ca2+-uptake was examined in a crude synaptosome preparation from adult rat brains. 5-Methoxytryptol, 5-methoxytryptamine, melatonin and 6-chloromelatonin (10(-8)-10(-6) M) depressed significantly the K+-stimulated increase in Ca2+-uptake, without affecting the basal, unstimulated Ca2+-uptake by synaptosomes. At 10(-6) M concentration the following order of potency was found: 6-chloromelatonin greater than or equal to 5-methoxytryptamine greater than 5-methoxytryptophol greater than or equal to melatonin. Serotonin did not affect significantly either basal or stimulated Ca2+-uptake.