Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC166
Melatonin Inhibits Membrane Depolarisation-Induced Calcium Signals in Cultured Rat Trigeminal Ganglion Neurons
D. Aydin1, O. F. Kalkan1, E. Kacar2, M. Ozcan3, A. Ayar1
1. Department of Physiology, Karadeniz Technical University Faculty of Medicine, Trabzon, Turkey. 2. Department of Physiology, University of Firat, Faculty of Medicine, Elazig, Turkey. 3. Department of Biophysics, University of Firat, Faculty of Medicine, Elazig, Turkey.
Acute or chronic orofacial pain is a symptom associated with disorders of oral soft and hard tissues, and represents a common problem of modern society. Trigeminal ganglion neurons, orofacial nociceptors, are primary sensory neurons that have proven to be an efficient cellular model for studying orofacial pain mechanisms. Free intracellular calcium is a ubiquitous second messenger being involved in a wide range of neuronal functions including control of excitability and neurotransmitter release, and nociceptive signal transmission. We have investigated, by considering intracellular calcium concentrations as a key signal for nociceptive transmission, the effects of melatonin on membrane depolarization-induced calcium signalling in rat trigeminal ganglia neurons. Trigeminal neurons were cultured on glass coverslips following enzymatic digestion and mechanical agitation, and loaded with the calcium sensitive dye fura-2 AM (1 uM). Intracellular calcium responses in individual trigeminal neurons were quantified by using standard fura-based ratiometric calcium imaging technique. All data were analyzed by using unpaired t test, P <.05 defining statistical significance. Exposure to melatonin caused a dose dependent inhibition of high KCl (30 mM)-induced increase in intracellular calcium levels. The cells were depolarized with brief exposure to KCl (30 mM) (100±0.0%, n=9 cells) and extracellularly applied melatonin (10 uM) caused a significant inhibition in concomitantly applied 30 mM KCl-induced increase in intracellular calcium (30 mM KCl + 10 uM melatonin: 99.3±1.1%, n=984.5±3.4 %, n=9, P<0.05) which was recovered within 5 minutes (30 mM KCl: 99.3±1.1%, n=9). A 5-minute of treatment with 100 uM melatonin also caused a significant and reversible inhibition of intracellular calcium increase due to KCl application (first 30 mM KCl: 100±0.0% (n=10), 30 mM KCl + 100 uM melatonin: 72.1±3.8 % (P<0.05, n=10), recovery 30 mM KCl: 98.6±1.5%, n=10). Our results indicates that the pineal hormone melatonin may have potential to treat orofacial pain as well as indicating possible involvement of impaired levels this endogenous agent in pathogenesis of chronic orofacial pain conditions that are difficult to treat.
Where applicable, experiments conform with Society ethical requirements