Abstract
Cell swelling enhances a slowly activating delayed rectifier K+ current (IKs) in cardiac cells. This investigation was undertaken to determine which of the two structural units reconstituting the IKs channel, KCNQ1 (KvLQT1) and KCNE1 (minK/IsK), plays a key role in the cell swelling-induced IKs enhancement and to dissect a possible involvement of tyrosine phosphorylation therein. KCNQ1 was transiently expressed alone or together with KCNE1 in a heterologous mammalian cell line. Two distinct whole-cell membrane currents were separately observed during the exposure of transfected cells to various degrees of hyposmotic solutions. A hyposmotic challenge (0.7 times control osmolarity) resulted in about a twofold increase not only in the heteromeric KCNQ1/KCNE1, but also in the homomeric KCNQ1 channel currents. There was no significant difference in the incremental ratio of current amplitude in response to hyposmotic stress between the two KCNQ1-related currents, and the cells expressing the heteromeric channels swelled less than those with the homomeric channels or without the exogenous ones. The cell swelling-induced IKs enhancement was not affected by a protein tyrosine kinase (PTK) inhibitor, by genistein (50 μM), or by an inhibitor of phosphotyrosine phosphatase (PTP), orthovanadate (500 μM), or a nonhydrolyzable ATP analogue, AMP-PNP (5 mM). Taken together, it is very likely that KCNQ1 might primarily participate in the IKs enhancement by osmotic cell swelling. The obligatory dependence of the IKs augmentation on PTK activity remained to be demonstrated, at least, in this expression system.
