Involvement of Ca2+-dependent PKCs in the adaptive changes of mu-opioid pathways to sympathetic denervation in the guinea pig colon.
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(2+)-dependent PKC activity was reduced in colonic myenteric plexus synaptosomes. The mu-opioid agent, DAMGO, increased Ca(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(2+)-dependent PKC isoforms betaI, betaII and gamma decreased, whereas alpha levels increased. In whole-mount preparations, the four Ca(2+)-dependent PKC isoforms co-localized with mu-opioid receptors on subpopulations of colonic myenteric neurons. The percentage of neurons staining for PKCbetaII, as well as the number of mu-opioid receptor-positive neurons staining for PKCbetaII, decreased in denervated preparations. The same parameters related to PKCalpha, betaI or gamma remained unchanged. Overall, the present data strengthen the concept that mu-opioid receptors located on myenteric neurons are coupled to Ca(2+)-dependent PKCs. After chronic sympathetic denervation, a reduced efficiency of this coupling may predominantly involve PKCbetaII, although also PKCbetaI and gamma, but not PKCalpha, may be implicated.
Giaroni
C
C
Department of Clinical Medicine, Section of Experimental and Clinical Pharmacology, University of Insubria, via O. Rossi 9, Varese, Italy. cristina.giaroni@uninsubria.it
Zanetti
E
E
Pascale
A
A
Oldrini
R
R
Canciani
L
L
Giuliani
D
D
Amadio
M
M
Chiaravalli
A M
AM
Lecchini
S
S
Frigo
G M
GM
D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D003106:Colon / Q000294:innervation*; D003714:Denervation; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D006168:Guinea Pigs; D007150:Immunohistochemistry; D008297:Male; D011493:Protein Kinase C / Q000378:metabolism*; D017450:Receptors, Opioid, mu / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology*
D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D011493:Protein Kinase C; D002118:Calcium