Tang T, Stevens B A, Cox B M
Department of Pharmacology, Uniformed Services University of Health Sciences, Bethesda, MD 20814-4799, USA.
J Neurosci Res. 1996 May 15;44(4):338-43. doi: 10.1002/(SICI)1097-4547(19960515)44:4<338::AID-JNR4>3.0.CO;2-D.
Opioid agonists induced an increase in the intracellular free calcium concentration ([Ca2+]i) or an inhibition of K+ (25 mM)-stimulated increase in [Ca2+]i in different subsets of mouse dorsal root ganglion (DRG) neurons. The total neuronal population was grouped into three classes according to somatic diameter and defined as small ( < 16 microns), intermediate (16-25 microns), or large ( > 25 microns) neurons. Substance P-like immunoreactivity was detected mainly in the small and intermediate neurons. The delta, kappa, and mu opioid receptor agonists [D-Ser2,Leu5]enkephalin-Thr (DSLET), U69593, and [D-Ala2, MePhe4, Glyol5]enkephalin (DAMGO) each induced a transient increase in [Ca2+]i in a small fraction ( < 30%) of neurons. The increases in [Ca2+]i were blocked by the opioid antagonist naloxone. The dihydropyridine-sensitive calcium channel blocker nifedipine also blocked the increase in [Ca2+]i induced by 1 microM DSLET. The rank order of potency (percentage of cells responding to each opioid agonist) was DSLET > U69593 > DAMGO. The opioid-induced increase in [Ca2+]i was observed mainly in large neurons, with a low incidence in small and intermediate neurons. Opioid agonists also caused inhibition of K(+)-stimulated increases in [Ca2+]i, which were blocked by naloxone (1 microM). Inhibition of the K(+)-stimulated increase by 1 microM DSLET or U69593 was greater in small and intermediate neurons than in large neurons.
阿片类激动剂可诱导小鼠背根神经节（DRG）神经元不同亚群的细胞内游离钙浓度（[Ca2+]i）升高，或抑制钾离子（25 mM）刺激引起的[Ca2+]i升高。根据体细胞直径，将整个神经元群体分为三类，分别定义为小（<16微米）、中（16 - 25微米）或大（>25微米）神经元。P物质样免疫反应主要在小神经元和中神经元中检测到。δ、κ和μ阿片受体激动剂[D-Ser2，Leu5]脑啡肽-苏氨酸（DSLET）、U69593和[D-Ala2，MePhe4，Glyol5]脑啡肽（DAMGO）各自在一小部分（<30%）神经元中诱导[Ca2+]i短暂升高。[Ca2+]i的升高被阿片拮抗剂纳洛酮阻断。二氢吡啶敏感的钙通道阻滞剂硝苯地平也阻断了1 microM DSLET诱导的[Ca2+]i升高。效力顺序（对每种阿片激动剂有反应的细胞百分比）为DSLET > U69593 > DAMGO。阿片诱导的[Ca2+]i升高主要在大神经元中观察到，在小神经元和中神经元中的发生率较低。阿片激动剂还可抑制钾离子刺激引起的[Ca2+]i升高，这被纳洛酮（1 microM）阻断。1 microM DSLET或U69593对钾离子刺激升高的抑制在小神经元和中神经元中比在大神经元中更明显。
