Opioid-induced inhibition of voltage-gated calcium channels parallels expression of omega-conotoxin-sensitive channel subtype during differentiation of NG108-15 cells.
Depolarization-induced increases in intracellular free calcium concentration ([Ca2+]i) were measured in single NG108-15 cells using indo-1 based microfluorimetry. In cells differentiated for 6 days in serum-free forskolin (5 microM) supplemented media, application of micromolar concentrations of [D-Ala2-D-Leu5]enkephalin (DADLE) inhibited Ca2+ influx mediated by voltage-gated Ca2+ channels. Inhibition of 50 mM K(+)-induced Ca2+ influx by DADLE was concentration-dependent over the range of 0.1 to 10 microM and blocked by 100 microM naloxone. Differentiation increased the amplitude of depolarization-induced [Ca2+]i transients from 78 +/- 21 nM in undifferentiated cells to 1,282 +/- 318 nM after 6 days. One microM nitrendipine inhibited Ca2+ influx by at least 65% at all stages of differentiation, while sensitivity to omega-conotoxin GVIa (omega-CgTx) did not appear until day 3. omega-CgTx inhibited a dihydropyridine-sensitive Ca2+ channel. DADLE inhibition of Ca2+ channels did not appear until 3 days of differentiation. Thus, opioid inhibition of depolarization-induced Ca2+ influx paralleled the expression of omega-CgTx sensitive voltage-gated Ca2+ channels.
Jin
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Department of Pharmacology, University of Minnesota, Medical School, Minneapolis 55455.
Lee
N M
NM
Loh
H H
HH
Thayer
S A
SA
D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects; D005576:Colforsin / Q000494:pharmacology; D003470:Culture Media; D003592:Cytophotometry; D004723:Endorphins / Q000494:pharmacology*; D016308:Enkephalin, Leucine-2-Alanine / Q000494:pharmacology; D005910:Glioma / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects*; D009423:Nervous System Neoplasms / Q000378:metabolism; D009447:Neuroblastoma / Q000378:metabolism; D010456:Peptides, Cyclic / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D003470:Culture Media; D004723:Endorphins; D010456:Peptides, Cyclic; D005576:Colforsin; D016308:Enkephalin, Leucine-2-Alanine; D020866:omega-Conotoxin GVIA