An in vitro invastigation of the effects of ophiorphin on nociceptive calcium signaling rat sensory neurons

Pain is a process that inceptive from periphery and transmit to central nervous system. Dorsal root ganglions are the first stopping place where the cell bodies of nociceptors are present. Increase of intracelluler free calcium levels in these neurons has a key role in pain transmission. In these study, the effects of ophiorphin on [Ca2+]i levels in rat DRG cell culture were examined.DRGs were removed from 1?2 day old neonatal rats and DRG neurons were isolated by enzymatic and mechanical procedures. Cells were loaded with a fluorescent dye fura?2. Intracelluler free calcium [Ca2+]i (ex.340/380 nm em.@ 510 nm) levels were studied with a microscopic digital image analysis system. All data were analyzed by using unpaired t test, P <.05 defining statistical significance.Treatment with opiorphin for 30 minutes caused a complete inhibition of cytosolic calcium responses to KCl (30 mM). The mean 340/380 nm ratio was increased from baseline level of 0.79±0.05 (n=67) to 1.24±0.06 with KCl exposure (30 mM KCl, P<0.05, n= 67) which remained without significant change at 5th minute but abolished after 30 minute treatment with 100 uM opiorphin (30 mM KCl + 100 uM opiorphin: 0.78±0.07, n=55).We report for the first time in these peripheral nociceptive sensory neurones that opiorphin inhibits membrane depolarisation-induced calcium signalling. Although this effect takes time, considering the fact that opiorphin advantages with respect to the abuse liability and drug tolerance, this agent or its proper derivatives are promising candidates for treatment of pain conditions.Key words: Pain, ophiorphin, DRG neurons, calcium, nociception