TY - JOUR T1 - Opioid receptors modulate diverse types of calcium channels in the nucleus tractus solitarius of the rat JF - The Journal of Neuroscience JO - J. Neurosci. SP - 7608 LP - 7615 DO - 10.1523/JNEUROSCI.14-12-07608.1994 VL - 14 IS - 12 AU - H Rhim AU - RJ Miller Y1 - 1994/12/01 UR - http://www.jneurosci.org/content/14/12/7608.abstract N2 - We have investigated the coupling between opioid receptors and different types of Ca2+ channels in neurons acutely isolated from the nucleus tractus solitarius (NTS) of the rat. Using fura-2-based imaging we found that Ca2+ transients evoked by depolarization with 50 mM KCl were suppressed by the mu-opioid receptor agonist D-Ala2,N-MePhe4,Gly5- ol-enkephalin (DAMGO) and less effectively by the kappa-receptor agonist U-69,593. The delta-receptor agonist D-Pen2,D-Pen5-enkephalin (DPDPE) was ineffective. In whole-cell voltage-clamp recordings from these neurons, depolarizing voltage steps elicited high-threshold Ca2+ currents that could be distinguished pharmacologically into different components. Part of the current could be blocked by dihydropyridines, part by omega-conotoxin-GVIA and part by omega-agatoxin-IVA. This suggests that the neurons contained L-, N-, and P/Q-type Ca2+ channels. DAMGO and U-69,593 both blocked part of the Ca2+ current but DPDPE was ineffective. Perfusion of GTP-gamma-S into the cells produced a rapid rundown of the Ca2+ current and occluded further effects of the opioid agonists, suggesting the involvement of a G-protein in the coupling mechanism. Inhibition of L-channels did not alter the effect of DAMGO. On the other hand inhibition of N-channels occluded about 80% of the effect of DAMGO. Inhibition of the P/Q-current occluded the remainder of the DAMGO effect. Thus, it appears that activation of opioid receptors can inhibit N- and P/Q-type Ca2+ channels but not L-channels in these cells. It is likely that such effects are important in opioid- mediated inhibition of transmitter release in the brain. ER -