Two Isoforms of the Human Voltage Gated Proton Channel hHV1

Abstract

The human voltage gated proton channel, hHV1, regulates pH in the respiratory tract, sperm capacitation, histamine secretion, the phagocyte respiratory burst, and B lymphocyte signaling. Although only one proton channel gene has been identified to date in any species, hHV1 is present in B lymphocytes in two forms, Long and Short. The Long form is the full-length protein, 273 amino acids. The Short form lacks the first 20 amino acids at the N terminus, and is the result of translation from an alternative initiation site. We generated plasmids that produce Long or Short form channels in heterologous expression systems, and characterized the channels by patch voltage clamp. Although Long and Short form channels were generally similar, in perforated-patch studies the Short form had a more pronounced response to PMA (phorbol ester) stimulation. In leukocytes, hHV1 has two distinct gating modes. Compared with its properties in resting cells, hHV1 opens faster, closes more slowly, the maximum conductance, gH,max, increases, and the gH-V relationship shifts negatively by 40 mV during the respiratory burst when NADPH oxidase is actively producing reactive oxygen species. PMA is a potent and effective activator of both NADPH oxidase and the enhanced gating mode of hHV1, by virtue of its activation of PKC (protein kinase C). Perhaps by selectively expressing a higher fraction of Long or Short channels, cells can fine-tune their responsiveness.Support: NSF MCB-0943362, NIH R01-GM087507 to TD, Bennett Fellowship from Leukaemia and Lymphoma Research (ref n: 12002) (MC).