Voltage-dependent modulation of single N-Type Ca2+ channel kinetics by receptor agonists in IMR32 cells.
The voltage-dependent inhibition of single N-type Ca(2+) channels by noradrenaline (NA) and the delta-opioid agonist D-Pen(2)-D-Pen (5)-enkephalin (DPDPE) was investigated in cell-attached patches of human neuroblastoma IMR32 cells with 100 mM Ba(2+) and 5 microM nifedipine to block L-type channels. In 70% of patches, addition of 20 microM NA + 1 microM DPDPE delayed markedly the first channel openings, causing a four- to fivefold increase of the first latency at +20 mV. The two agonists or NA alone decreased also by 35% the open probability (P(o)), prolonged partially the mean closed time, and increased the number of null sweeps. In contrast, NA + DPDPE had little action on the single-channel conductance (19 versus 19.2 pS) and minor effects on the mean open time. Similarly to macroscopic Ba(2+) currents, the ensemble currents were fast activating at control but slowly activating and depressed with the two agonists. Inhibition of single N-type channels was effectively removed (facilitated) by short and large depolarizations. Facilitatory pre-pulses increased P(o) significantly and decreased fourfold the first latency. Ensemble currents were small and slowly activating before pre-pulses and became threefold larger and fast decaying after facilitation. Our data suggest that slowdown of Ca(2+) channel activation by transmitters is mostly due to delayed transitions from a modified to a normal (facilitated) gating mode. This single-channel gating modulation could be well simulated by a Monte Carlo method using previously proposed kinetic models predicting marked prolongation of first channel openings.
Carabelli
V
V
Dipartimento di Neuroscienze, Corso Raffaello 30, Torino, Italy.
Lovallo
M
M
Magnelli
V
V
Zucker
H
H
Carbone
E
E
D001464:Barium / Q000494:pharmacology; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D015220:Calcium Channels / Q000502:physiology*; D020881:Enkephalin, D-Penicillamine (2,5)-; D004745:Enkephalins / Q000494:pharmacology*; D006801:Humans; D015640:Ion Channel Gating; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008956:Models, Chemical; D009447:Neuroblastoma; D009638:Norepinephrine / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D014407:Tumor Cells, Cultured
D002120:Calcium Channel Agonists; D015220:Calcium Channels; D004745:Enkephalins; D001464:Barium; D020881:Enkephalin, D-Penicillamine (2,5)-; D009638:Norepinephrine