Melatonin Receptor‐Mediated Stimulation of Phosphoinositide Breakdown in Chick Brain Slices

Abstract

The direct effect of melatonin and related agonists on Li+‐amplified phosphoinositide breakdown was studied in chick brain slices prelabeled with myo‐[2‐3H]‐inositol. The melatonin receptor agonist 6‐chloromelatonin (10–100 µM) increased, in a concentration‐dependent manner, the accumulation of inositol phosphates (IP) in chick brain slices. This effect of 6‐chloromelatonin (10 µM) was rapid as transient increases in IP3/IP4 (maximal increase, 29% at 20 s) and IP2 levels (maximal increase, 36% at 1 min) were observed, followed by a slower but sustained increase in IP1 level (30% at 5 min), when the amount of IP3/IP4 and IP2 had already been decreased to the control level. The phosphoinositide response elicited by 6‐chloromelatonin (10 µM) was dependent on the presence of extracellular calcium. Direct stimulation of membrane phospholipase C by 6‐chloromelatonin (10 µM) in isolated myo‐[2‐3H]inositol‐prelabeled optic tectum membranes was dependent on the presence of guanosine‐5′‐O‐(3‐thio)triphosphate (1 µM), thus suggesting that G protein(s) link melatonin receptor activation to phospholipase C stimulation. The competitive melatonin receptor antagonist luzindole (10–100 µM) inhibited in a concentration‐dependent manner the IP1 accumulation stimulated by 6‐chloromelatonin (10–100 µM); however, it did not affect the accumulation stimulated by 5‐hydroxytryptamine (10 µM). By contrast, methysergide (10 µM) completely inhibited 5‐hydroxytryptamine (10 µM)‐, but not 6‐chloromelatonin (10 µM)‐, induced IP1 accumulation. Melatonin receptor agonists increased IP1 accumulation in a concentration‐dependent manner reaching different maximal responses. N‐Acetyl‐5‐hydroxytryptamine was more potent than melatonin in increasing IP1 accumulation, suggesting activation of a melatonin receptor site other than the ML‐1 melatonin receptor (i.e., N‐acetyl‐5‐hydroxytryptamine ≥ melatonin). In conclusion, these results demonstrate that activation of a melatonin receptor with pharmacological characteristics different from those of the ML‐1 subtype leads to activation of the phospholipase C‐mediated signal transduction pathway.

Role of melatonin on diabetes-related metabolic disorders

“…In contrast to the uniform cAMP-dimishing effect of melatonin, both IP3-increasing [61,62] as well as IP3-decreasing [63,64] effects of melatonin have been described in different cell types. Previous studies in INS1 insulinoma cells indicated a dose-dependent stimulation of IP3 release by melatonin, while the competitive melatonin receptor antagonist luzindole was able to completely abolish such IP3-liberating effects of melatonin, thus giving strong evidence for the involvement of melatonin receptors [65] .…”

Phosphatidylinositol 4,5-Bisphosphate Modifies Tubulin Participation in Phospholipase Cβ1Signaling

“…After sonication (as described above) and centrifugation at 20,000 ϫ g for 15 min (4°C), the supernatants were extracted with water-saturated ether and neutralized with 1 M NH 4 HC O 3 . Ion exchange chromatography (Dowex AG 1-X8 resin, formate form; BioRad) of the samples was performed as described previously (Popova and Dubocovich, 1995). Total [ 3 H]inositol phosphates were quantified by liquid scintillation counting.…”

“…Endogenous phosphoinositide pools of SK-N-SH cells were prelabeled with myo-[ 3 H]inositol (Popova and Dubocovich, 1995), and carbachol-induced inositol phosphate generation was studied in colchicine-treated or control cells (Fig. 8).…”

Melatonin and N-acetyl-serotonin cross the red blood cell membrane and evoke calcium mobilization in malarial parasites

“…Melatonin and N-acetyl-serotonin (NAS) are thought to induce IP 3 generation in different systems such as hamster melanoma cells (17), pigeon brain (18), chick brain (19), and dinoflagellates (20). The ability of IP 3 to mobilize Ca 2+ from intracellular stores and therefore to trigger many biological processes such as cell division is well known (21).…”