Abstract
Identification of a mechanosensing domain is central to the biophysics of stretch-activated (SA) channels. Here, we identify that Stress-axis Regulated Exon (STREX), a particular amino-acid sequence at the C-terminus of the stretch-activated, large-conductance, calcium- and voltage-activated potassium (BKCa) channels cloned from chick embryonic heart (we designated as SAKCa channels), is responsible for the stretch sensitivity through the interaction with cytoskeletal complex (EF1a/actin). Deletion of the STREX insert diminished the stretch sensitivity of the channel. Sequence analysis revealed that the ERA 672-674 sequence of the chick STREX is indispensable for channel stretch sensitivity and single amino acid substitution from Ala674 to Thr674 completely eliminated the stretch sensitivity. Co-expression of chick STREX-EGFP and SAKCa in CHO cells, induced a strong GFP signal in the cell membrane and inhibited the stretch sensitivity significantly, implying that the STREX requires binding partner(s) to contribute to the stretch sensitivity. We found that actin and elongation factor 1A (EF-1α) bind specifically to chick STREX and the knockdown of EF-1α by siRNA treatment severely inhibited the stretch sensitivity of SAKCa. These results suggest that SAKCa senses membrane tension through an interaction between STREX and cytoskeletal complex such as actin and EF-1α. [Jpn J Physiol 55 Suppl:S133 (2005)]
