Distinct subcellular mechanisms for the enhancement of the surface membrane expression of SK2 channel by its interacting proteins, α‐actinin2 and filamin A

Abstract

The normal function of ion channels depends critically on the precise subcellular localization and the number of channel proteins on the cell surface membrane. Small-conductance, Ca -activated K channels (SK, K 2) are expressed in human atrial myocytes and are responsible for shaping atrial action potentials. Understanding the mechanisms of SK channel trafficking may provide new insights into the regulation controlling the repolarization of atrial myocytes. We have previously demonstrated that the C- and N-termini of SK2 channels interact with the actin-binding proteins α-actinin2 and filamin A, respectively. However, the roles of the interacting proteins on SK2 channel trafficking remain incompletely understood. Using total internal reflection fluorescence (TIRF) microscopy, we studied the mechanisms of surface membrane localization of SK2 (K 2.2) channels. When SK2 channels were co-expressed with filamin A or α-actinin2, the membrane fluorescence intensity of SK2 channels increased significantly. We next tested the effects of primaquine and dynasore on SK2 channels expression. Treatment with primaquine significantly reduced the membrane expression of SK2 channels. In contrast, treatment with dynasore failed to alter the surface membrane expression of SK2 channels. Further investigations using constitutively active or dominant-negative forms of Rab GTPases provided additional insights into the distinct roles of the two cytoskeletal proteins on the recycling processes of SK2 channels from endosomes. α-Actinin2 facilitated recycling of SK2 channels from both early and recycling endosomes while filamin A probably aids the recycling of SK2 channels from recycling endosomes.

Sex‐specific activation of SK current by isoproterenol facilitates action potential triangulation and arrhythmogenesis in rabbit ventricles

“…; Zhang et al . ). It is possible that differential channel trafficking properties exist between sexes and contribute to different I KAS responses to sympathetic stimulation.…”

Coupling of SK channels, L-type Ca2+ channels, and ryanodine receptors in cardiomyocytes

“…Negative controls with secondary antibodies alone were performed for all experiments. For testing the SK2 antibody, Human Embryonic Kidney (HEK) 293 cells were cultured and transfected by human cardiac SK2 plasmid using the similar methods we reported before 32 .…”

Small-conductance Ca2+-activated K+ channels: insights into their roles in cardiovascular disease

“…SK2 channels directly interact with α-actinin2 and MLC2 via their C-termini and with filamin A via their N-termini 26 . New insights into the regulation controlling the repolarization of the atrial myocytes have demonstrated that α-actinin2 facilitates the recycling of SK2 channels from both early and late endosomes, while filamin A likely assists in the recycling of SK2 channels from recycling endosomes 27 .…”