Opioid elevation of intracellular free calcium: possible mechanisms and physiological relevance.
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+](i) 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.
Samways
Damien S K
DS
Department of Pharmacological and Physiological Science, Health Science Center, School of Medicine, Saint Louis University, MO, USA. samwayds@slu.edu
Henderson
Graeme
G
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D006801:Humans; D011957:Receptors, Opioid / Q000378:metabolism*; D009435:Synaptic Transmission
D011957:Receptors, Opioid; D002118:Calcium