UBC Theses and Dissertations
Modulation of cardiac voltage-gated potassium channel functional expression by Kinesin I and small GTPases Cheng, Yvonne
Functional expression of voltage-gated potassium (Kv) channels in the plasmalemma is essential for repolarization phase of the cardiac action potential. Therefore, changes in Kv channel plasmalemmal expression can impact cardiac action potential duration and thereby result in arrythmias. The expression of these Kv channels is modulated by a number of different mechanisms, and among these, the most important and potent one is the regulation of the number of channels in the plasma membrane through modulation of channel trafficking. The trafficking process of Kv channel in cardiac background is poorly understood. The purpose of the studies presented in this thesis was to identify the specific kinesin isoform that is required for cardiac Kv1.5 channel forward trafficking and to investigate the roles of small GTPases in the trafficking of Kv4.2 channels in adult rat ventricular myocytes. Overexpression of wild type Kif5b increased the Kv1.5-conducted current and this increase was dependent on Golgi function; a 6 h treatment with Brefeldin A reduced Kv1.5 currents to control levels in Kif5b-overexpressing cells. Expression of dominant negative isoform of Kif5b prior to induction of Kv1.5 in a tetracycline inducible system blocked surface expression of the channel in both HEK293 cells and H9c2 cardiomyoblasts. These data confirmed the requirement for Kif5b for forward trafficking of newly synthesized Kv1.5 channels. The involvement of several Rab GTPases as well as Sar1 in the trafficking of an endogenous cardiomyocyte potassium channel has also been established. Kv4.2 traffics out of the cardiac endoplasmic reticulum via a conventional pathway involving Sar1 and Rab1 and its trafficking to the sarcolemma is enhanced by overexpression of wild type Rab11. Internalization of the channels is dependent upon Rab5 function and block of Rab4 somehow also inhibits that internalization. The internalized channels, if not recycle back into plasma membrane will be degraded via the proteasomal degradation pathway. Together, these studies enhance our knowledge of the players involved in the trafficking pathway of Kv channels in cardiomyocytes. In particular, the roles of kinesin and several small GTPases in regulating cardiac Kv channel plasmmalemmal expression through channel trafficking modulation.
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