Mechanosensitivity of STREX-lacking BKCa channels in the colonic smooth muscle of the mouse

Abstract

Stretch sensitivity of Ca2+-activated large-conductance K+ channels (BKCa) has been observed in a variety of cell types and considered to be a potential mechanism in mechanoelectric transduction (MET). Mechanical stress is a major stimulator for the smooth muscle in the gastrointestinal (GI) tract. However, much about the role and mechanism of MET in GI smooth muscles remains unknown. The BKCa shows a functional diversity due to intensive Slo I alternative splicing and different α/β-subunit assembly in various cells. The stress-regulated exon (STREX) insert is suggested to be an indispensable domain for the mechanosensitivity of BKCa. The purpose of this study was to determine whether the BKCa in colonic myocytes of the adult mouse is sensitive to mechanical stimulation and whether the STREX insert is a crucial segment for the BKCa mechanosensitivity. The α- and β1-subunit mRNAs and the α-subunit protein of the BKCa channels were detected in the colonic muscularis. We found that the BKCa STREX-lacking variant was abundantly expressed in the smooth muscle, whereas the STREX variant was not detectable. We demonstrated that the STREX-lacking BKCa channels were also sensitive to membrane stretch. We suggest that in addition to the STREX domain, there are other additional structures in the channel responsible for mechanically coupling with the cell membrane.