Abstract
Melatonin plays an important role in the immune regulation of birds. Both endogenous and exogenous melatonin modulates lymphocyte proliferation via its specific membrane receptors, Mel1a, Mel1b and Mel1c, though the mechanisms behind this process are poorly understood. We investigated the differences in melatonin membrane receptor Mel1a, Mel1b and Mel1c expression by western blot and reverse transcription reaction and the in vitro effect of melatonin on the intracellular Ca2+ concentration ([Ca2+]i) in splenocytes of the Indian Jungle Bush Quail, Perdicula asiatica. We used a non-selective melatonin receptor antagonist for Mel1a and Mel1b, luzindole, and the selective Mel1b blocker, 4P-PDOT to check the specific role of melatonin receptor on ([Ca2+]i). The expression of Mel1a, Mel1b and Mel1c receptors mRNA and protein was upregulated by melatonin (10−7 M) with a significant high rise in ([Ca2+]i), which was differentially blocked by supplementation of antagonist, luzindole (10−7 M) and 4P-PDOT (10−7 M). Furthermore, we noted in vitro effect of melatonin and 2-aminoethoxydiphenyl borate (2-APB), a cell-permeable antagonist of inositol 1, 4, 5-trisphosphate (IP3) receptor to check the rise in ([Ca2+]i) through the IP3 pathway. Significantly low ([Ca2+]i) was noted in melatonin and 2-APB pretreated splenocytes when compared with splenocytes where 2-APB was absent. Thus, our data suggest that melatonin through its membrane receptor induced the elevation of ([Ca2+]i) via IP3-dependent pathway for splenocyte proliferation in P. asiatica.
Acknowledgements
Instrument gift by Alexander von Humboldt Foundation, Bonn, Germany to CH is highly acknowledged. A Senior Research Fellowship from Indian Council of Medical Research, New Delhi, India awarded to SKY is also highly acknowledged.