P376Ophiobolins redistribute Kv4.x ion channels and connexin26 in cardiac muscle

Background: Ophiobolins are sesterpene-type secondary metabolites, mostly synthesized by some plant pathogenic fungi (e.g. Bipolaris). Most of the microbial secondary metabolites have substantial effects on humans and animals but the background of their action is poorly known. The synapse-associated protein 97 (SAP97) anchors Kir and Kv ion channels regulating the subcellular translocation and localization of channels. The gap junction protein connexin26 facilitates direct intercellular communication but its role in the heart is indefinite. Aim: In this study we compared the expression and distribution of Kv4.x ion channels, their modulators and connexin26 in cardiomyopathic heart in the presence of ophiobolin as an external stress factor for myocytes. We used rat heart tissues and rat cardiomyocytes using molecular biology methods. Results: We revealed that the Kv4.3 pattern differs from that of Kv4.2 because only Kv4.3 marked the Z-line which is the localization place of the T-tubular system. Ophiobolin P1 (OP1) treatments down-regulated and redistributed the Kv4.2 and Kv4.3 ion channels in the plasma membrane as well as in the mitochondrial and nuclear membrane. Another effect was that the synapse-associated protein 97 did not colocalize with the Kv4.x ion channel α-subunits at the sarcolemma compared to the controls. Atomic force microscope study showed that the Young modulus and the mechanical parameters are altered on the cell surface after 1 day in the presence of OP1. The SAP97 and Kv4 channel subunits colocalize at the sarcolemma of healthy cardiomyocytes but the distribution of these complexes has changed under ophiobolin treatment. Discussion: These results suggest that the anchoring SAP97 and its modulator functions are crucial to maintain the normal ITO current in the heart tissues. In the tripartite complex of Kv4.3-SAP97-CAMKII structure are need to form the physiologically active Kv4 type channels and essential to regulate the subcellular localization of channels in the cardiomyocytes. This work was supported by grants TAMOP-4.2.2.A-11/1/KONV-2012-0035 and TAMOP-4.2.2.A-11/1/KNOV-2012-0052.