Involvement of Ca super(2+)-dependent PKCs in the adaptive changes of mu -opioid pathways to sympathetic denervation in the guinea pig colon

• Published in: Biochemical pharmacology 2009-11, Vol.78 (9), p.1233-1241
• Main Authors: Giaroni, C, Zanetti, E, Pascale, A, Oldrini, R, Canciani, L, Giuliani, D, Amadio, M, Chiaravalli, A M, Lecchini, S, Frigo, G M
• Format: Article
• Language: English
• ISSN: 0006-2952
• DOI: 10.1016/j.bcp.2009.06.107

In the guinea pig colon, chronic sympathetic denervation entails supersensitivity to inhibitory mu - opioid agents modulating cholinergic neurons. The mechanism underlying such adaptive change has not yet been unravelled, although protein kinase C (PKC) may be involved. A previous study indirectly demonstrated that activation of mu -opioid receptors on myenteric neurons facilitates PKC activity. Such coupling may counteract the inhibitory action of mu -opioid agents on acetylcholine overflow, since PKC, per se, increases this parameter. After chronic sympathetic denervation such restraint abates, representing a possible mechanism for development of supersensitivity to mu -opioid agents. In the present study, this hypothesis was further investigated. After chronic sympathetic denervation, Ca super(2+)-dependent PKC activity was reduced in colonic myenteric plexus synaptosomes. The mu -opioid agent, DAMGO, increased Ca super(2+)-dependent PKC activity in synaptosomes obtained from normal, but not from denervated animals. In myenteric synaptosomes obtained from this experimental group, protein levels of Ca super(2+)-dependent PKC isoforms beta I, beta II and gamma decreased, whereas alpha levels increased. In whole-mount preparations, the four Ca super(2+)-dependent PKC isoforms co- localized with mu -opioid receptors on subpopulations of colonic myenteric neurons. The percentage of neurons staining for PKC beta II, as well as the number of mu -opioid receptor-positive neurons staining for PKC beta II, decreased in denervated preparations. The same parameters related to PKC alpha , beta I or gamma remained unchanged. Overall, the present data strengthen the concept that mu -opioid receptors located on myenteric neurons are coupled to Ca super(2+)-dependent PKCs. After chronic sympathetic denervation, a reduced efficiency of this coupling may predominantly involve PKC beta II, although also PKC beta I and gamma , but not PKC alpha , may be implicated.