Integrin‐dependent and ‐independent potentiation of BKCa channel current by cell stretch

Abstract

The large conductance, calcium‐activated K+(BKCa) channel is an important regulator of stretch‐induced contraction of VSM. Integrins are involved in this process because α5β1 and αvβ3 integrin blocking antibodies prevent myogenic constriction. Recent studies in our lab indicate that fibronectin (FN), an endogenous α5β1 integrin ligand, enhances BKCa channel current through both Ca2+‐ and phosphorylation‐dependent mechanisms in native VSMCs or HEK293 cells transfected with BKCa cDNA. To test whether BKCa channels are mechanosensitive and the possible role of integrins in this process, patch clamp methods were used to investigate the properties of either native or heterologously expressed BKCa channels by stretch of single cells plated onto a flexible substrate. Thin silicone membranes were coated with either FN or poly‐l‐lysine (PLL) to assess integrin‐dependent and ‐ independent responses, respectively, and stretched using two blunt micropipettes driven in equal and opposite directions by piezoelectric translators. Graded stretch to 130% of resting cell length induced graded increases in BKCa current (up to 95%) in HEK 293 cells expressing murine BKCa channel α‐subunits (mSlo). No potentiation was evident in mock transfected cells (n=10). The increase in current was ~2‐fold greater for cells adhering to FN (n=9) than for cells on PLL (n=7). On FN, 130% longitudinal stretch of primary VSM cells (n=3) caused ~2x potentiation of the basal outward current, and ~3x potentiation of the iberiotoxin‐sensitive current. Our results suggest that the BKCa channel can be potentiated by membrane stretch, with one component due to intrinsic mechanosensitivity of the channel and a second component due to signaling through an integrin‐dependent process.