Abstract
The ability of action-potential-like waveforms (APWs) to attenuate opioid-induced inhibition of N-type Ca2+ channels was investigated in the neuroblastoma × glioma cell line NG108–15 using whole-cell voltage clamp methods. In in vitro differentiated NG108–15 cells, the opioid agonist [d-ala2]-methionine-enkephalin (DAME) reversibly decreased ω-conotoxin-GVIA-sensitive Ba2+ currents (N-type currents). Agonist-mediated inhibition of N-type currents could be transiently relieved by strong unphysiological depolarizing prepulses to +80 mV (facilitation). Significant facilitation was also achieved by conditioning the cell with a train of 15 APWs, which roughly mimicked physiological action potentials (1- to 6-ms-long depolarizations to +30 mV from a holding potential of –40 mV). The APW-induced facilitation depended on both conditioning pulse frequency and duration. Summation of the disinhibition produced by each APW was possible because reinhibition following repolarization to –40 mV was a much slower process (τ=88 ms) than the onset of facilitation at +80 mV (τ=7 ms). These results provide evidence that N-type Ca2+ channel facilitation may be a physiologically relevant process, and suggest that neuronal firing may relieve agonist-induced inhibition of N-type currents to an extent depending on both the shape of action potentials and the frequency of firing.
Similar content being viewed by others
Author information
Authors and Affiliations
Additional information
Received: 14 September 1998 / Accepted: 29 September 1998
Rights and permissions
About this article
Cite this article
Tosetti, P., Taglietti, V. & Toselli, M. Action-potential-like depolarizations relieve opioid inhibition of N-type Ca2+ channels in NG108–15 cells. Pflügers Arch 437, 441–448 (1999). https://doi.org/10.1007/s004240050799
Issue Date:
DOI: https://doi.org/10.1007/s004240050799