The Strex-Insert in a Stretch-Activated BK Channel from Chick Heart is not Enough for Conferring GsMTx-4 Inhibitory Effect on mSlo1

Abstract

The mechanotoxin 4 (GsMTx-4), isolated from Grammostola spatulata, has been widely used to identify mechanosensitive (MS) channels in sensory system, but the mechanism how this toxin inhibits MS channels still remains elusive. By studying a stretch-activated (SA), large conductance (BK, Slo1) (SAKca) channel from chick heart and expressed in CHO cells, we show that µM GsMTx-4 inhibits SAKca channel current completely in the excised inside-out configuration, but deletion of the STREX exon, a 59-amino acid insert between RCK1 and RCK2 domain in BK channel, diminished the inhibitory effect of the peptide. To investigate whether the STREX insert in SAKca is the interaction (directly or indirectly) domain for GsMTx-4 effect, we constitute a chimeric construct by inserting the 59-amino acid sequence (STREX exon) from SAKca channel into mSlo1 in the location between RCK1 and RCK2 domains and expressed it in Xenopus oocytes. Our results show that although the insertion of STREX into mSlo1 increased stretch-sensitivity of mSlo1, µM GsMTx-4 has no effect on the chimeric channel. We concluded that STREX-insert is not enough for conferring GsMTx-4 inhibitory effect on mSlo1, some special elements in SAKca might also be involved in channel interaction with GsMTx-4.