Connexin-based channels comprise hemichannels and gap junction channels. The opening of hemichannels allow for the flux of ions and molecules from the extracellular space into the cell and vice versa. Similarly, the opening of gap junction channels permits the diffusional exchange of ions and molecules between the cytoplasm and contacting cells. The controlled opening of hemichannels has been associated with several physiological cellular processes; thereby unregulated hemichannel activity may induce loss of cellular homeostasis and cell death. Hemichannel activity can be regulated through several mechanisms, such as phosphorylation, divalent cations and changes in membrane potential. Additionally, it was recently postulated that redox molecules could modify hemichannels properties in vitro. However, the molecular mechanism by which redox molecules interact with hemichannels is poorly understood. In this work, we discuss the current knowledge on connexin redox regulation and we propose the hypothesis that extracellular cysteine could be important for sensing changes in redox potential. Future studies on this topic will offer new insight into hemichannel function, thereby expanding the understanding of the contribution of hemichannels to disease progression.

Calcium and voltage-activated potassium (BK) channels are key actors in cell physiology, both in neuronal and non-neuronal cells and tissues. Through negative feedback between intracellular Ca2+ and membrane voltage, BK channels provide a damping mechanism for excitatory signals. Molecular modulation of these channels by alternative splicing, auxiliary subunits and post-translational modifications showed that these channels are subjected to many mechanisms that add diversity to the BK channel α subunit gene. This complexity of interactions modulates BK channel gating, modifying the energetic barrier of voltage sensor domain activation and channel opening. Regions for voltage as well as Ca2+ sensitivity have been identified, and the crystal structure generated by the 2 RCK domains contained in the C-terminal of the channel has been described. The linkage of these channels to many intracellular metabolites and pathways, as well as their modulation by extracellular natural agents, has been found to be relevant in many physiological processes. This review includes the hallmarks of BK channel biophysics and its physiological impact on specific cells and tissues, highlighting its relationship with auxiliary subunit expression.

Calcium- and voltage-activated potassium channels (BK) are regulated by a multiplicity of signals. The prevailing view is that different BK gating mechanisms converge to determine channel opening and that these gating mechanisms are allosterically coupled. In most instances the pore forming α subunit of BK is associated with one of four alternative β subunits that appear to target specific gating mechanisms to regulate the channel activity. In particular, β1 stabilizes the active configuration of the BK voltage sensor having a large effect on BK Ca ²⁺ sensitivity. To determine the extent to which β subunits regulate the BK voltage sensor, we measured gating currents induced by the pore-forming BK α subunit alone and with the different β subunits expressed in Xenopus oocytes (β1, β2IR, β3b, and β4). We found that β1, β2, and β4 stabilize the BK voltage sensor in the active conformation. β3 has no effect on voltage sensor equilibrium. In addition, β4 decreases the apparent number of charges per voltage sensor. The decrease in the charge associated with the voltage sensor in α β4 channels explains most of their biophysical properties. For channels composed of the α subunit alone, gating charge increases slowly with pulse duration as expected if a significant fraction of this charge develops with a time course comparable to that of K ⁺ current activation. In the presence of β1, β2, and β4 this slow component develops in advance of and much more rapidly than ion current activation, suggesting that BK channel opening proceeds in two steps.

Voltage-gated proton (Hv) channels play an essential role in phagocytic cells by generating a hyperpolarizing proton current that electrically compensates for the depolarizing current generated by the NADPH oxidase during the respiratory burst, thereby ensuring a sustained production of reactive oxygen species by the NADPH oxidase in phagocytes to neutralize engulfed bacteria. Despite the importance of the voltage-dependent Hv current, it is at present unclear which residues in Hv channels are responsible for the voltage activation. Here we show that individual neutralizations of three charged residues in the fourth transmembrane domain, S4, all reduce the voltage dependence of activation. In addition, we show that the middle S4 charged residue moves from a position accessible from the cytosolic solution to a position accessible from the extracellular solution, suggesting that this residue moves across most of the membrane electric field during voltage activation of Hv channels. Our results show for the first time that the charge movement of these three S4 charges accounts for almost all of the measured gating charge in Hv channels.

Significance: H _v 1 proton channels, since their open probability increases with depolarization and low pH, are fundamental in sustaining the suitable pH gradient for cell survival. Here, we have characterized the gating current elicited by the monomeric mutant proton channel N264R with the aim of understanding the voltage-dependent processes that control channel opening. Gating currents precede ion currents, indicating that a large fraction of gating charge is displaced before H _v 1 opening. The voltage sensor displacements are complex and consist of numerous well-defined states. However, most of the charge is displaced in a single transition that probably leads to channel opening. The positively charged arginine in the N264R channel promotes gating charge trapping in addition to blocking the proton currents.

Significance: Acid extrusion in various types of cells and the reactive oxygen species production by the NADPH oxidase in phagocytes and microglia are mediated by the voltage-gated proton channel (H _v 1). One of the biophysical properties essential for the H _v 1 function is its ΔpH-dependent gating. Here, we measured the H _v 1 gating currents’ pH dependence in the monomeric nonconducting D160N Ciona intestinalis H _v 1 mutant. We demonstrated that H _v 1 ΔpH-dependent gating is a consequence of voltage sensor modulation by direct gating currents recordings. Around 60% of the energy stored in the ΔpH is coupled to the H _v 1 voltage sensor activation. Therefore, the proton chemical energy is transduced to the voltage sensor activation in H _v 1 to produce ΔpH-dependent gating.