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Abstract: Caveolin-3, the major caveolin isoform in cardiomyocytes, plays an important role in the rapid signaling pathways initiated by stimulation of the membrane-associated molecules. To examine the role of caveolin-3 in regulating estrogen receptor α in cardiomyocytes, we investigate whether the membrane estrogen receptor α associates with caveolin-3 and whether this association is linked to the 17β-estradiol-mediated signals. In control cardiomyocytes, following discontinuous sucrose gradient centrifugation, caveolin-3 was found predominantly in the lipid raft buoyant fractions, whereas it was distributed to both the buoyant and non-lipid raft heavy fractions following metabolic inhibition treatment. Confocal microscopy showed that estrogen receptor α co-localized with caveolin-3 on the plasma membrane of neonatal and adult rat cardiomyocytes. This membrane labeling of estrogen receptor α was not seen following treatment with the cholesterol-depleting agent methyl-β-cyclodextrin (5mM), whereas metabolic inhibition had little effect on the membrane distribution of estrogen receptor α. Metabolic inhibition induced tyrosine phosphorylation of caveolin-3 and decreased its association with estrogen receptor α, both effects being mediated via a Src activation mechanism, since they were inhibited by the selective tyrosine kinase inhibitor PP2. Metabolic inhibition also induced tyrosine phosphorylation of connexin43 and increased its association with c-Src, both effects being prevented by 17β-estradiol (200nM). The effect of 17β-estradiol on metabolic inhibition-induced tyrosine phosphorylation of connexin43 was inhibited by the specific estrogen receptor antagonist ICI182780. These data identify cardiac caveolin-3 as juxtamembrane scaffolding for estrogen receptor α docking at caveolae, which provide a unique compartment for conveying 17β-estradiol-elicited, rapid signaling to regulate connexin43 phosphorylation during ischemia. [Copyright &y& Elsevier]

Abstract: We have demonstrated that activation of ATP-sensitive potassium (KATP) channels can attenuate sympathetic hyperinnervation. Sildenafil, a phosphodiesterase-5 inhibitor, has been shown to provide a preconditioning-like cardioprotective effect via opening of KATP channels. The aim of this study was to investigate whether chronic administration of sildenafil attenuates cardiac sympathetic hyperinnervation after myocardial infarction through activation of KATP channels and to compare it with the nitric oxide donor isosorbide dinitrate. Male Wistar infarcted rats induced by ligation of the anterior descending artery were randomized to either vehicle, nicorandil, sildenafil, isosorbide dinitrate, glibenclamide, or a combination of nicorandil and glibenclamide, or sildenafil and glibenclamide. Myocardial norepinephrine levels revealed a significant elevation in vehicle-treated rats compared with sham-operated rats, consistent with sympathetic hyperinnervation after infarction assessed by immunohistochemical analysis for tyrosine hydroxylase, growth associated factor 43 and neurofilament and by protein expression and mRNA of nerve growth factor. Sympathetic hyperinnervation was reduced after administering either nicorandil or sildenafil. Arrhythmic scores during programmed stimulation in the sildenafil-treated rats were significantly lower than those treated with the vehicle. Furthermore, the beneficial effects of sildenafil-induced were reversed by the addition of either glibenclamide or 5-hydroxydecanoate, implicating mitochondrial KATP channels as the relevant target. Isosorbide dinitrate failed to confer similar antiarrhythmia. 1H-[1,2,4]oxadiazolo[4,3-α]quinoxalin-1-one, a soluble guanylyl cyclase inhibitor, did not influence the effect of sildenafil on the nerve growth factor. These data indicate that sildenafil after infarction attenuated sympathetic hyperinnervation and arrhythmias by activation of mitochondrial KATP channels through a guanylyl cyclase-cGMP-independent pathway. [Copyright &y& Elsevier]

Highlights: [•] HYS-32 is a new analogue of combretastatin A-4 containing a cis-stilbene moiety. [•] We investigate the effect of HYS-32 on Cx43 gap junctions in rat primary astrocytes. [•] HYS-32 enhances Cx43 expression and GJIC via a PKC–ERK signaling cascade. [•] HYS-32 prevents LPS-induced downregulation of Cx43 and inhibition of GJIC. [•] The effects of HYS-32 on astrocytes potentiate its application in neuroprotection. [Copyright &y& Elsevier]