Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC174
Leptin activates intracellular calcium signals in isolated rat dorsal root ganglion neurons
S. Oruc1, M. Ozcan1, N. Aslan1, S. Kutlu2, H. Kelestimur2, A. Ayar3
1. Biophysics, Firat University Faculty of Medicine, Elazig, Turkey. 2. Physiology, Firat University Faculty of Medicine, Elazig, Turkey. 3. Physiology, Karadeniz Technical University Faculty of Medicine, Trabzon, Turkey.
Central and peripheral administration of leptin has been suggested to cause proalgesic actions but the mechanism of action is not clear. This study investigate the effects of leptin on intracellular calcium, ([Ca2+]i), levels in isolated rat dorsal root ganglion (DRG) neurons, with the aim of exploring possible involvement of leptin-mediated signalling in peripheral nociception. DRG neurons were isolated from neonatal rats, plated on poly-d-lysine-coated coverslips. Isolated DRG neurons were loaded with 1 μmol Fura-2 AM and Ca2+ responses were assessed by using the fluorescent ratiometry. Fura-2 loaded DRG cells were excited at 340 and 380 nm, and emission was recorded at 510 nm by using digital microscopic calcium imaging system. Changes in free intracellular calcium concentrations were determined by the change in 340/380nm ratio in individual DRG neurons. All data were analyzed by using unpaired t test, with a one-tailed P level of <0.05 defining statistical significance. Leptin caused increase in [Ca2+]i in a dose dependent manner. The mean 340/380 nm ratios were (baseline 100.0±0.0% vs leptin): 104.6±0.4% (0.1µM Leptin, n= 22 cells), 119.5±3.9 % (1µM Leptin, n=23 cells) and 129.4±4.2% (10 µM Leptin, n=27 cells), following addition of respective concentrations of leptin. The PKC inhibitor chelerythrine chloride significantly decreased the leptin (1µM)-induced calcium responses (from 100.0±0.0% to 56.7±6.4%, n=27 cells). After depletion of thapsigargin-sensitive calcium stores by treatment of cells with thapsigargin (TG) attenuated but not completely blocked the subsequent calcium response to 1µM leptin (TG +1µM Leptin = 106.1±2.4% (n=18 cells) vs. 1µM Leptin= 119.5±3.9 (n=23 cells). In sum we found that leptin mediate peripheral nociceptive signalling through mechanism that involves PKC-dependent changes in intracellular calcium levels in rat primary sensory neurons. Results from this study indicates that in addition to mediating the sensing of energy reserves in the body, leptin involved in the sensing process of pain.
Where applicable, experiments conform with Society ethical requirements