Involvement of Cyclooxygenase-2 in Carbachol-Induced Positive Inotropic Response in Mouse Isolated Left Atrium

Abstract

The mouse heart is expected to have characteristic contractile properties. However, basic information on the function of the mouse heart has not been accumulated sufficiently. In this study, the involvement of cyclooxygenase (COX)-2 in carbachol (CCh)-induced inotropic response was investigated in mouse isolated left atrium. Influences of CCh and their mechanisms of action on developed tension elicited by electrical stimulation were examined pharmacologically. The presence of COX-2 in atrium was examined by Western blotting and immunohistochemical analysis. CCh (3 M for 15 min) produced a biphasic inotropic response: a transient decrease in contractile force followed by a late increase. Atropine suppressed the biphasic inotropic response to CCh. A muscarinic M 3 receptor antagonist, 4-diphenyl-acetoxy-N-methlpiperidine, inhibited the late positive inotropic action. Blockade of prostaglandin (PG) E 2 or F 2␣ receptor by 6-isopropoxy-9-oxoxanthene-2-carboxylic acid (AH6809) or 9␣, 15R-dihydroxy-11␤-fluoro-15-(2,3-dihydro-1H-inden-2-yl)-16,17,18,19,20-pentanor-prosta 5Z, 13E-dien-1-oic acid (AL8810), respectively, significantly suppressed the positive inotropic response to CCh. A nonselective COX inhibitor, indomethacin, and a selective COX-2 inhibitor, N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulfonamide (NS-398) inhibited the positive response. A COX-1 inhibitor, valeroyl salicylate, did not affect the positive response. The positive response was almost completely abolished in the endocardial endothelium-deprived atria. Existence of COX-2 in endocardial endothelium was confirmed by Western blotting and immunohistochemical analysis. The present study indicated that the CCh-induced positive inotropic response was mediated by PGs, possibly PGE 2 and PGF 2␣ , released in part from endocardial endothelium. Furthermore, for the first time, we demonstrated that the production of PGs depended in part on COX-2 in endocardial endothelium through the muscarinic M 3 receptor stimulation.

Muscarinic Stimulation Facilitates Sarcoplasmic Reticulum Ca Release by Modulating Ryanodine Receptor 2 Phosphorylation Through Protein Kinase G and Ca/Calmodulin-Dependent Protein Kinase II

“…54–57 This variability in results could be attributed to the complex nature of muscarinic regulation of SR Ca release demonstrated here, including reciprocal changes in RyR2 phosphorylation mediated by two different MR subtypes.…”

Urothelial/Lamina Propria Spontaneous Activity and the Role of M3 Muscarinic Receptors in Mediating Rate Responses to Stretch and Carbachol

“…Of interest is the report that the frequency of transient calcium and membrane potential changes in bladder myofibroblasts is also increased during muscarinic receptor stimulation . In some tissues activation of muscarinic receptors stimulates the production of prostaglandins (Hara et al, 2009) or nitric oxide, (Andersson et al, 2008) however the U&LP contractile responses to carbachol were insensitive to indomethacin and L-NNA.…”

Prostaglandin FP receptor antagonists: discovery, pharmacological characterization and therapeutic utility

“…Moreover, Hara et al . () showed that the muscarinic receptor‐mediated positive ionotropic response of mouse isolated left atrium was actually mediated by endogenously released PGs, including PGF 2α , since amongst other PG receptor antagonists, AL‐8810 significantly blunted the response to carbachol. In another related study, it was shown that while PGF 2α significantly decreased the chronotropic response to cholinergic stimulation of isolated atria from endotoxin‐treated rats (Nikoui et al, ), AL‐8810 or indomethacin was able to counteract and reverse this phenomenon.…”