Calcium influx in rat thalamic relay neurons through voltage-dependent calcium channels is inhibited by enkephalin.
High and low voltage-activated, transient (HVA and LVA,T) Ca2+ currents are crucial in determining the characteristic thalamic firing pattern, during the oscillatory mode. The modulatory effects induced by D-ala2-D-leu5-enkephalin (DADLE) on voltage-dependent Ca2+ channels have been investigated on acutely dissociated neurons from rat ventro-basal (VB) thalamus, by means of whole cell patch-clamp technique. DADLE (400 nM) reduced HVA Ca2+ channel currents in 37 out of 44 cells tested (-53 +/- 5.3% to 0 mV test potential, n = 24,). In 50% of the cases DADLE induced an effect which was persistent at all the potentials tested, i.e. a voltage-independent one. In the remaining neurons, the inhibition partially or totally disappeared on the currents evoked at the highest potentials. DADLE was also able to inhibit LVA Ca2+ channels (-40% in five out of 12 cells). In conclusion, thalamic relay neurons present opioid receptors negatively coupled to both HVA and LVA Ca2+ channels. The presence of two inhibitory effects of DADLE on the total HVA Ca2+ channels has been observed, and they are distinguishable on the basis of their sensitivity to voltage. It is suggested that Ca2+ current modulation may play a role in the production and tuning of the rhythmic burst discharge in these neurons.
Formenti
A
A
Istituto di Fisiologia Umana II, Università Statale di Milano, Italy.
Arrigoni
E
E
Martina
M
M
Taverna
S
S
Avanzini
G
G
Mancia
M
M
D000818:Animals; D001464:Barium / Q000037:antagonists & inhibitors / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D004594:Electrophysiology; D016308:Enkephalin, Leucine-2-Alanine / Q000494:pharmacology; D004745:Enkephalins / Q000494:pharmacology*; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D013788:Thalamus / Q000166:cytology / Q000378:metabolism*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004745:Enkephalins; D001464:Barium; D016308:Enkephalin, Leucine-2-Alanine; D002118:Calcium