ABSTRACT
Title
A functional cross-talk between cannabinoid CB1 and muscarinic M3 receptors increases the contractile responses of the bovine ciliary muscle
Authors
M. R. Romano, M. D. Lograno
Dipartimento Farmaco-Biologico, Università di Bari "Aldo Moro", Via Orabona 4, 70125 Bari
Dipartimento Farmaco-Biologico, Università di Bari "Aldo Moro", Via Orabona 4, 70125 Bari
Abstract
Purpose: Recent evidences have demonstrated a functional interaction between Gq/11-coupled receptors and cannabinoid system. We explored whether a possible cross-talk between cannabinoid CB1 receptors and muscarinic system, both widely expressed in the ocular structure, influenced contractile response of the ciliary smooth muscle. Although it is well accepted that cannabinoids modulate the intraocular pressure, it is not known whether the endocannabinoids are involved in more complex circuits by interacting with other systems. The aim of the present study was to investigate possible interactions between cannabinoid CB1receptors and muscarinic system in the contractility control of bovine ciliary muscle.
Methods:The ciliary muscle strips isolated by bovine eyes were exposed cumulatively to anandamide in the presence and in the absence of carbachol (10 nM), in a miograpf system for isometric recording. The experiments were also conducted in the presence of AM251 (50 and 100 nM), a selective cannabinoid CB1 receptor antagonist, 4-DAMP (100 nM) a selective M3 muscarinic receptor antagonist. Contractile responses were expressed as the percentage of 10 mM carbachol-induced contraction.
Key findings:Anandamide produced, concentration dependently, contractions in bovine ciliary muscle strips and this effect was enhanced by the previous stimulation of Gq-protein-coupled M3muscarinic receptors with carbachol. AM251, cannabinoids CB1receptors, and 4-DAMP, muscarinic M3receptors. The contractile response to anandamide plus carbachol was affected by selective antagonists of each receptor, pertussis toxin, phospholipase C, protein kinase C and Rho kinase inhibitor.
Conclusion: These data suggest that sequential activation of M3muscarinic receptors and cannabinoid CB1receptors produce synergistic contractile effects in the bovine ciliary muscle which involve the activation of Rho kinase and protein kinase C.
Methods:The ciliary muscle strips isolated by bovine eyes were exposed cumulatively to anandamide in the presence and in the absence of carbachol (10 nM), in a miograpf system for isometric recording. The experiments were also conducted in the presence of AM251 (50 and 100 nM), a selective cannabinoid CB1 receptor antagonist, 4-DAMP (100 nM) a selective M3 muscarinic receptor antagonist. Contractile responses were expressed as the percentage of 10 mM carbachol-induced contraction.
Key findings:Anandamide produced, concentration dependently, contractions in bovine ciliary muscle strips and this effect was enhanced by the previous stimulation of Gq-protein-coupled M3muscarinic receptors with carbachol. AM251, cannabinoids CB1receptors, and 4-DAMP, muscarinic M3receptors. The contractile response to anandamide plus carbachol was affected by selective antagonists of each receptor, pertussis toxin, phospholipase C, protein kinase C and Rho kinase inhibitor.
Conclusion: These data suggest that sequential activation of M3muscarinic receptors and cannabinoid CB1receptors produce synergistic contractile effects in the bovine ciliary muscle which involve the activation of Rho kinase and protein kinase C.