Dynorphin A selectively reduces a large transient (N-type) calcium current of mouse dorsal root ganglion neurons in cell culture.

Abstract

Opioid receptors are differentially coupled to ion channels. IA-and 6-opioid receptors are coupled to calciumand/or voltage-dependent potassium channels and K-opioid receptors are coupled to voltage-dependent calcium channels. Using the single-electrode voltage-clamp technique, we investigated the effect of the K-opioid receptor agonist dynorphin A on somatic calcium currents of mouse dorsal root ganglion (DRG) neurons in culture. Three different calcium currents were recorded: a small transient current activated positive to -60 mV; a large, inactivating current activated positive to -50 mV; and a moderate, slowly inactivating current activated positive to -40 mV. The first was less sensitive to cadmium block than the others. These calcium currents were similar to those described in other cells, which have been designated T, N, and L calcium currents, respectively. The opioid peptide dynorphin A reduced calcium current by selectively reducing the large inactivating (N) calcium current. Naloxone, an opioid receptor antagonist, reversed this action of dynorphin A. N calcium current is the predominant calcium current in DRG neurons. If N calcium channels are present in primary afferent terminals, and if they are coupled to K-opioid receptors as in the soma, these results suggest a mechanism by which dynorphin A inhibits calcium influx and neurotransmitter release.Recent studies have established that multiple opioid receptors including ,-, 8-, and K-Opioid receptors are present in the nervous system (1-4) and that they are differentially coupled to ion channels (5-10). ,u-and 3-opioid receptors have been shown to be coupled to potassium channels (5-8, 11, 12 (35)(36)(37). Recently, a third type of calcium current was described in chick DRG neurons (38). The three calcium currents had different activation and inactivation voltage ranges, and the calcium channels had different conductances and kinetics. The currents were differentially affected by the calcium channel blocker cadmium, the agonist dihydropyridine Bay K 8644, and the antagonist dihydropyridines (38)(39)(40). The calcium currents were designated T, N, and L by Nowycky et al. (38).These observations raise the possibility that the K-opioid receptor could be linked to one or more calcium channel types. In the present study we recorded three different somatic calcium currents in mouse DRG neurons and assessed the effect of dynorphin A on these T, N, and L calcium currents. MATERIALS AND METHODSCell Culture. DRG neurons were grown in cell culture as described (41). Spinal cords, with DRG attached, were dissected from 12-to 14-day fetal mice and mechanically dissociated. The resulting suspension was plated onto 35-mm collagen-coated dishes at various densities, usually about one-eighth cord per dish. Initial medium contained 5% horse serum and 5% Nu-Serum (Collaborative Research, Waltham, MA) in minimum essential medium (MEM) (Eagle's; GIBCO). Nerve growth factor (NGF) was added at a final concentration of 10 ng/ml. After 4-5 days in culture, 5'-fluoro...

Voltage‐gated calcium currents in cultured embryonic Xenopus spinal neurones.

“…These measurements were made to facilitate comparison of the Ca21 currents in embryonic Xenopus neurones to those in other excitable cells, and as preliminaries for the examination of depolarizationinduced increase in [Ca2+]i presented in the following paper (Barish, 1991). llet-enkephalin HVA-relaxing current was selectively inhibited by opiates, as described by Gross & MacDonald (1987) for the K-preferring agonist dynorphin A in mouse DRG neurones. Bixby & Spitzer (1983) observed that methionine-enkephalin (Tyr-GlyGly-Phe-Met; Met-enkephalin) at a concentration of 20 IaM reduced the Ca21-dependent action potential of embryonic Xenopus Rohon-Beard neurones.…”

Voltage-dependent effects of opioid peptides on hippocampal CA3 pyramidal neurons in vitro

“…Ca2+ conductances might also be altered. Opiates, including dynorphin A (Gross et al, 1990), can alter Ca'+ currents in several neuron types (Gross and MacDonald, 1987;Crain and Shen, 1990;Surprenant et al, 1990;Regan et al, 1991;Seward et al, 1991). Such a Ca'+ channel effect is interesting in the light of recent studies suggesting a role for intracellular Ca'-+ in the regulation of I, in sympathetic ganglia neurons (Beech et al,199 1;Kirkwood et al,199 1;Marrion et al,199 1).…”

Interaction of Opiate Peptides with Dopamine Effects on Prolactin Secretion and Membrane Electrical Properties in Anterior Pituitary Cells from Lactating Rats

“…However, it appears noteworthy to indicate that in other preparations, i.e. in dorsal root ganglia cells (49). in helix neurons (50) o r in neuroblastoma cells (5 l), opiates o r opiate-like substances have different actions.…”