Currents through Hv1 channels deplete protons in their vicinity

Abstract

The pH-sensitive fluorescent protein Venus can be used as an optical reporter for proton flux when fused to an intracellular domain of Hv1 channels.

Asymmetrically Positioned Flagellar Control Units Regulate Human Sperm Rotation

“…The concentration of a significant number of proton channels in such a small cellular domain as a flagellum in the close proximity to the pH-sensitive Ca 2+ channel CatSper likely affects sperm physiology in a profound way. While the direct measurement of the intracellular pH changes due to sperm Hv1 activity has not been done yet, the fact that Hv1 has a powerful ability to deplete protons in its vicinity has been recently shown (De-la-Rosa et al, 2016). We have confirmed this finding by in silico estimation of the steady-state level of pH that might be reached in the neighborhood of a single Hv1 dimer.…”

Asymmetrically Positioned Flagellar Control Units Regulate Human Sperm Rotation

“…The concentration of a significant number of H + channels in such a small cellular domain as a flagellum in close proximity to the pH-sensitive CatSper likely affects sperm physiology in a profound way. Although direct measurement of the intracellular pH changes because of sperm Hv1 activity has not been possible, the fact that Hv1 has a powerful ability to deplete protons in its vicinity has been recently shown (De-la-Rosa et al, 2016). We have confirmed this finding by in silico estimation of the steady-state level of pH that might be reached in the neighborhood of a single Hv1 dimer.…”

“…These results support our finding and explain why Hv1 needs to be positioned close to CatSper to ensure local alkalinity, just enough to upregulate only a portion of CatSper channels. Given the fact that Hv1 can significantly change the pH locally (De-la-Rosa et al, 2016), is expressed in human sperm at high density, and is physiologically active (Lishko et al, 2010), Hv1 can produce a significant local alkaline shift. However, such pH changes will occur in nanodomains that are localized only on one side of the flagellum and are likely active only while the sperm cell moves.…”

Fluorescent Visualization of Cellular Proton Fluxes

“…However, the pH gradient (6.8 – 7.2) observed across neighboring cells indicates that the majority of the protons emanating from a patch clamped cell are freely diffusing in the bath solution. These proton accumulation and diffusion results also highlight that open Hv-1 channels not only deplete the local intracellular proton concentration (De-la-Rosa et al, 2016), but also raise the extracellular proton concentration tens of microns away from the cell perimeter.…”

“…We initially dismissed inward proton currents through Hv-1 channels because the outward proton gradient used would require hyperpolarization less than − 90 mV. However, it has been recently shown that Hv-1 channels can deplete the local proton concentration on the intracellular side of the channel (De-la-Rosa et al, 2016), raising the possibility that the local proton driving force could be vastly different than the bulk proton gradient. Indeed, holding Hv-1 channels open for 4 s at 100 mV in the absence of a pH gradient created a substantial inward proton gradient, which was detected as an inward tail current when the channels were closed at 0 mV (Figure S5, blue trace).…”