Samways Damien S K, Henderson Graeme
Department of Pharmacological and Physiological Science, Health Science Center, School of Medicine, Saint Louis University, MO, USA.
Cell Signal. 2006 Feb;18(2):151-61. doi: 10.1016/j.cellsig.2005.08.005. Epub 2005 Sep 30.
Opioid receptors are seven transmembrane domain Gi/G0 protein-coupled receptors, the activation of which stimulates a variety of intracellular signalling mechanisms including activation of inwardly rectifying potassium channels, and inhibition of both voltage-operated N-type Ca2+ channels and adenylyl cyclase activity. It is now apparent that like many other Gi/G0-coupled receptors, opioid receptor activation can significantly elevate intracellular free Ca2+ ([Ca2+]i), although the mechanism underlying this phenomenon is not well understood. In some cases opioid receptor activation alone appears to elevate [Ca2+]i, but in many cases it requires concomitant activation of Gq-coupled receptors, which themselves stimulate Ca2+ release from intracellular stores via the inositol phosphate pathway. Given the number of Ca2+-sensitive processes known to occur in cells, there are therefore a myriad of situations in which opioid receptor-mediated elevations of Ca2+ may be important. Here, we review the literature documenting opioid receptor-mediated elevations of [Ca2+]i, discussing both the possible mechanisms underlying this phenomenon and its potential physiological relevance.
