Abstract 2816: Depletion of Atrial Membrane Cholesterol Stimulates the Recruitment of Kv1.5 Channels From the Rab11-associated Recycling Endosome
Cholesterol is an important determinant of cardiac excitability. Moreover, lipid-lowering therapies such as statins exert antiarrhythmic effects. Cholesterol’s ability to modulate membrane physical properties and its direct or indirect effects on ion channels are still subject to debate.
Aim: Here, we examine the hypothesis that cholesterol modulates the turnover of voltage-gated potassium channels, based on previous observations showing that depletion of membrane cholesterol increases the atrial repolarizing current IKur.
Methods: Whole-cell currents and single-channel activity were recorded in rat adult atrial myocytes (AAM) or after transduction with hKv1.5-EGFP. Channel mobility and expression were studied using fluorescence recovery after photobleaching (FRAP) and 3-dimensional microscopy.
Results: In both native and transduced-AAMs, the cholesterol-depleting agent MβCD induced a delayed (~7min) increase in IKur. Single-channel recordings revealed an increased number of active Kv1.5 channels upon MβCD application. N-ethylmaleimide that inhibits SNARE-mediated fusion suppressed MβCD effect on IKur. Non-hydrolysable GTP analogues also suppressed MβCD effect pointing to the involvement of Rab GTP-ases. Rab11 was found to co-immunoprecipitate with hKv1.5-EGFP channels whereas Rab4 was hardly detectable. Moreover, qPCR analysis of Rab11 and Rab4 isoforms in both rat and human myocardium showed that Rab11a and Rab11b transcripts were more abundant than Rab4a and Rab4b (Rab4b<Rab4a<Rab11a<Rab11b). In myocytes, over-expression of Rab11 CA and not Rab4 CA reduced IKur. Rab11 dominant negative (DN) but not Rab4 DN prevented the MβCD-induced IKur increase. Finally, 3-dimensional microscopy showed a decrease in co-localization of Kv1.5 and Rab11 in MβCD-treated AAM.
Conclusion: Cholesterol regulates Kv1.5 channel expression by modulating its trafficking through the Rab11-associated recycling endosome. This compartment appears as an important submembrane pool of channels readily available for recruitment into the sarcolemma of myocytes. This process could be a major mechanism for the tuning of cardiac electrical properties.