Temporal changes in expression of connexin 43 after load-induced hypertrophy in vitro

Abstract

Upon remodeling of the ventricle after a provoking stimulus, such as hypertension, connections between adjacent myocytes may need to be "reformatted" to preserve a synchronization of excitation of the remodeling heart. In the mammalian heart, the protein connexin forms the gap junctions that allow electrical and chemical signaling communication between neighboring cells. We aim to elucidate whether mechanical load, in isolation, potentially changes the expression of connexin 43 (Cx43), the major isoform of the connexin family in the ventricle, and its phosphorylation. Cx43 expression levels and contractile function of multicellular rabbit cardiac preparations were assessed in a newly developed in vitro system that allows for the study of the transition of healthy multicellular rabbit myocardium to hyper- trophied myocardium. We found that in mechanically loaded cardiac trabeculae, C×43 levels remained stable for about 12 h and then rapidly declined. Phosphorylation at Ser368 declined much faster, being almost absent after2hofhigh-load conditions. No-load conditions did not affect C×43 levels, nor did phosphorylation at Ser368. The downregulation of C×43 under mechanical load did not correspond with the contractile changes that were observed. Furthermore, blocking paracrine activity of the muscle could only partially prevent the downregulation of C×43. Additionally, no effect of mechanical loading on the expression of N-cadherin and zonula occludens-1 was observed, indicating a specificity of the connexin response. High mechanical load induced a rapid loss of C×43 phosphorylation, followed by a decrease in C×43 protein levels. Paracrine factors are partly responsible for the underlying mechanism of action, whereas no direct correlation to contractile ability was observed. © 2009 the American Physiological Society.