Nonopioid receptor-mediated effects of U-50,488H on [Ca2+]i and extracellular dopamine in PC12 cells
✍ Scribed by Nuannoi Chudapongse; Seong-Youl Kim; Kenroh Sasaki; Robert E. Kramer; Ing K. Ho
- Publisher
- John Wiley and Sons
- Year
- 2003
- Tongue
- English
- Weight
- 116 KB
- Volume
- 74
- Category
- Article
- ISSN
- 0360-4012
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✦ Synopsis
The present studies were carried out to determine the effects of a -opioid receptor agonist on cytosolic Ca 2ϩ concentration, [Ca 2ϩ ] i , and extracellular dopamine in undifferentiated PC12 cells. The -opioid receptor agonist U-50,488H caused concentration-dependent increases in [Ca 2ϩ ] i and extracellular dopamine. Neither effect was blocked by the selective -opioid receptor antagonist nor-binaltorphimine. Increases in extracellular dopamine content and [Ca 2ϩ ] i caused by U-50,488H were correlated positively in the presence of extracellular Ca 2ϩ ; however, reduction of extracellular Ca 2ϩ abolished the increase in [Ca 2ϩ ] i , but not that in dopamine. The latter observation suggests that stimulation of exocytotic release is not the primary mechanism involved in the increase in extracellular dopamine caused by U-50,488H. Effects on dopamine synthesis or catabolism also seem unlikely because the enhancement of extracellular dopamine occurred rapidly, and the amount of a major metabolite of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), was not affected. In any event, neither the increase in [Ca 2ϩ ] i nor the increase in extracellular dopamine caused by U-50,488H is mediated by the -opioid receptor.