IP(3)R-mediated Ca(2+) release is modulated by anandamide in isolated cardiac nuclei.
Cannabinoids (CBs) are known to alter coronary vascular tone and cardiac performance. They also exhibit cardioprotective properties, particularly in their ability to limit the damage produced by ischaemia reperfusion injury. The mechanisms underlying these effects are unknown. Here we investigate the intracellular localisation of CB receptors in the heart and examine whether they may modulate localised nuclear Ca(2+) release. In isolated cardiac nuclear preparations, expression of both the inositol 1,4,5-trisphosphate receptor type 2 (IP(3)R) and CB receptors (CB(1)R and CB(2)R) was demonstrated by immunoblotting. Both receptors localised to the nucleus and purity of the nuclear preparations was confirmed by co-expression of the nuclear marker protein nucleolin but absence of cytoplasmic actin. To measure effects of IP(3)R and CBR agonists on nuclear Ca(2+) release, isolated nuclei were loaded with Fluo5N-AM. This dye accumulates in the nuclear envelope. Isolated nuclei responded to IP(3) with rapid and transient Ca(2+) release from the nuclear envelope. Anandamide inhibited this IP(3)-mediated release. Preincubation of nuclear preparations with either the CB(1)R antagonist (AM251) or the CB(2)R antagonist (AM630) reversed anandamide-mediated inhibition to 80% and 60% of control values respectively. When nuclei were pre-treated with both CBR antagonists, anandamide-mediated inhibition of IP(3)-induced Ca(2+) release was completely reversed. These results are the first to demonstrate the existence of cardiac nuclear CB receptors. They are also the first to show that anandamide can negatively modulate IP(3)-mediated nuclear Ca(2+) release. As such, this provides evidence for a novel key mechanism underlying the action of CBs and CBRs in the heart.
Currie
Susan
S
Division of Physiology and Pharmacology, Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK. susan.currie@strath.ac.uk
Rainbow
Richard D
RD
Ewart
Marie-Ann
MA
Kitson
Susan
S
Pliego
Esperanza Herradon
EH
Kane
Kathleen A
KA
McCarron
John G
JG
D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D063385:Cannabinoid Receptor Modulators / Q000494:pharmacology*; D002316:Cardiotonic Agents / Q000494:pharmacology*; D002467:Cell Nucleus / Q000378:metabolism*; D063388:Endocannabinoids; D006168:Guinea Pigs; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000819:agonists / Q000378:metabolism*; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D010750:Phosphoproteins; D053284:Polyunsaturated Alkamides / Q000494:pharmacology*; D016601:RNA-Binding Proteins; D043884:Receptor, Cannabinoid, CB1 / Q000819:agonists / Q000378:metabolism; D043885:Receptor, Cannabinoid, CB2 / Q000819:agonists / Q000378:metabolism; D000097796:Nucleolin
D001095:Arachidonic Acids; D002118:Calcium; D063385:Cannabinoid Receptor Modulators; D002316:Cardiotonic Agents; D063388:Endocannabinoids; D053496:Inositol 1,4,5-Trisphosphate Receptors; D010750:Phosphoproteins; D053284:Polyunsaturated Alkamides; D016601:RNA-Binding Proteins; D043884:Receptor, Cannabinoid, CB1; D043885:Receptor, Cannabinoid, CB2; D000097796:Nucleolin; C078814:anandamide