The neuropeptide GsMTx4 inhibits a mechanosensitive BK channel through the voltage-dependent modification specific to mechano-gating.

The cardiac mechanosensitive BK (Slo1) channels are gated by Ca2+, voltage, and membrane stretch. The neuropeptide GsMTx4 is a selective inhibitor of mechanosensitive (MS) channels. It has been reported to suppress stretch-induced cardiac fibrillation in the heart, but the mechanism underlying the specificity and even the targeting channel(s) in the heart remain elusive. Here, we report that GsMTx4 inhibits a stretch-activated BK channel (SAKcaC) in the heart through a modulation specific to mechano-gating. We show that membrane stretching increases while GsMTx4 decreases the open probability (Po) of SAKcaC. These effects were mostly abolished by the deletion of the STREX axis-regulated (STREX) exon located between RCK1 and RCK2 domains in BK channels. Single-channel kinetics analysis revealed that membrane stretch activates SAKcaC by prolonging the open-time duration (τO) and shortening the closed-time constant (τC). In contrast, GsMTx4 reversed the effects of membrane stretch, suggesting that GsMTx4 inhibits SAKcaC activity by interfering with mechano-gating of the channel. Moreover, GsMTx4 exerted stronger efficacy on SAKcaC under membrane-hyperpolarized/resting conditions. Molecular dynamics simulation study revealed that GsMTx4 appeared to have the ability to penetrate deeply within the bilayer, thus generating strong membrane deformation under the hyperpolarizing/resting conditions. Immunostaining results indicate that BK variants containing STREX are also expressed in mouse ventricular cardiomyocytes. Our results provide common mechanisms of peptide actions on MS channels and may give clues to therapeutic suppression of cardiac arrhythmias caused by excitatory currents through MS channels under hyper-mechanical stress in the heart.

Cloning and characterization of the rat Slo3 (KCa 5.1) channel: From biophysics to pharmacology.

BACKGROUND AND PURPOSE: The Slo3 potassium (KCa 5.1) channel, which is specifically expressed in the testis and sperm, is essential for mammalian male fertilization. The sequence divergence of the bovine, mouse and human Slo3 α-subunit revealed a rapid evolution rate across different species. The rat Slo3 (rSlo3) channel has not been cloned and characterized previously. EXPERIMENTAL APPROACH: We used molecular cloning, electrophysiology (inside-out patches and outside-out patches) and mutagenesis to investigate the biophysical properties and pharmacological characteristics of the rSlo3 channel. KEY RESULTS: The rat Slo3 channel (rSlo3) is gated by voltage and cytosolic pH rather than intracellular calcium. The characteristics of voltage-dependent, pH-sensitivity and activation kinetics of the rSlo3 channel differ from the characteristics of other Slo3 orthologues. In terms of pharmacology, the 4-AP blockade of the rSlo3 channel also shows properties distinct from its blockade of the mSlo3 channel. Iberiotoxin and progesterone weakly inhibit the rSlo3 channel. Finally, we found that propofol, one of the widely used general anaesthetics, blocks the rSlo3 channel from both intracellular and extracellular sides, whereas ketamine only blocks the rSlo3 channel at the extracellular side. CONCLUSION AND IMPLICATIONS: Our findings suggest that the rSlo3 channel possesses unique biophysical and pharmacological properties. Our results provide new insights into the diversities of the Slo3 family of channels, which are valuable for estimating the effects of the use of these drugs to improve sperm quality.