Role of BK‐β4 in hypo‐osmotic activation of large conductance, Ca‐sensitive K (BK) channels expressed in HEK293 cells.

Abstract

BK channels, which are comprised of pore forming α and accessory β‐subunits, have been shown to eliminate intracellular K in response to hypo‐osmotic swelling. However, the role of the β subunits in this process has not been determined. We used HEK293 cells stably expressing BK‐α and examined a role for transiently expressed BK‐β4 (90% expression rate) to modulate the response of BK to cell swelling. Using patch clamp analysis, we determined NPo (cell attached, ‐Vp = −40 mV) and the % of observed channels per patch. The NPo and % channels per patch of BK‐α expressed alone in cells in isotonic (290 mOsm) solution was 0.71±0.05 (n=3) and 53%, respectively. This value was not significantly different from the NPo and % channels per patch for BK‐α in hypotonic (200 mOsm) solution (0.62±0.17, n=3 and 41%, respectively). The NPo and % channels per patch of BK‐α plus BK–β4 was significantly greater in hypotonic solution (1.32±0.15, n=3 and 76%, respectively) than in isotonic solution (0.70±0.15, n=8 and 41%, respectively). Compared to isotonic solution, when cells expressing BK‐α/β4 were in hypotonic solution, BK‐α exhibited more intense immuno‐staining at the plasma membrane and BK‐β4 was increased at the plasma membrane (western blot; OD = 0.20 in isotonic and 0.49 in hypotonic). These data suggest that the BK‐β4 subunit is necessary for trafficking of BK‐α and BK‐β4 to the plasma membrane in response to hypo‐osmotic stress.