Low-Na increases ventricular gap junction resistivity and phosphorylation levels of connexin43 at Serine 368: Possible synergistic interaction between calcineurin and protein kinase C

WAHEED, A; SALVAGE, SC; ORLOWSKI, A; FRY, CH; AIELLO, EA; MICHAEL, A; JABR, RI

San Diego

Congreso; XXI World Congress of the international society of heart research; 2013

International Society of Heart Research

One of the main contributors to ventricular arrhythmias is abnormal action potential propagation due to slowed conduction velocity (CV). This is mainly caused by alterations to gap junction (GJ) channel conductance, i.e. an increased GJ resistivity, Rj . GJs in left ventricle are composed of serine-rich phosphoproteins known as connexins (Cx), in particular the Cx43 isoform. The functional Cx43-GJ conductance is modulated by the Cx43 phosphorylation state. One of the most studied serine (S) phosphorylation sites identified is Ser-368. It is only phosphorylated by PKC leading to decreased Cx43-GJ conductance. Ventricular arrhythmias are associated with raised [Ca2+]i. Such an increase enhances the activity of the serine-threonine, Ca2+/CaM- dependent protein phosphatase-3, calcineurin (Cn). We have shown that raising [Ca2+]i by rapid pacing or low-Na solution slowed CV and raised Rj in LV papillary muscle and such an effect was attenuated by the Cn inhibitor, cyclosporin A. So far, the role of Cn in modulating Rj is unclear, however previous data has implicated Cn in slowing CV in left ventricular papillary muscles.Under control conditions the calcineurin inhibitors cyclosporin-A and CAIP had no effect on Rj. Under control conditions the PKC inhibitor, chelerythrine decreased Rj. Raised [Ca2+]i in left ventricular myocardium increased Rj. The increase of Rj was sensitive to Cn and PKC inhibitors. Conditions that increased Rj also augmented phosphorylation of Cx43-S368 and decreased non-phosphorylated Cx43 at Ser-368 (Cx43-NP). Alterations to Cx43-pS368 and Cx43-NP in low-Na solution were prevented by cyclosporin-A and chelerythrine.We conclude that a rise of [Ca2+]i is associated with phosphorylation of Cx-43 Ser368 and an increase of Rj Cx43-S368 may only be phosphorylated by PKC. This site is thought to be masked by pSer365 under control conditions and dephosphorylation of Ser365 by calcineurin enables Ser368 to be phosphorylated by PKC thus increasing Rj.