Regulatory mechanisms of activity and expression of voltage-gated proton channels

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Mechanisms responsible for controlling the activity and expression of the voltage-gated proton (H^+) channels were studied in rat microglia and murine osteoclasts. In microglia, cell acidosis, either by extracellular lactoacidosis or by dialyzing cells with an acidic pipette solution induced cell swelling The H^+ current was increased in association with the cell swelling by a shift of the half-activation voltage to more negative potentials and by acceleration of the activation kinetics. The acidosis-induced cell swelling and the accompanying potentiation of the H^+ current required non-hydrolytic binding of intracellular ATP and were inhibited by agents affecting actin filaments (phalloidin and cytochalasin D). This potentiation of the H^+ channel might operate as a negative feedback mechanism to protect microglia from cytotoxic acidosis-induced swelling in the pathological CNS. Amplitudes of the H^+ current fluctuate at an interval of 10-30 min in some cells. Murine osteoclasts gener … More ated from bone-marrow cells in the presence of sRANK ligand exhibited a similar H^+ current, characterized by dependencies on both intracellular and extracellular pH, outward rectification, slow activation kinetics and blockade by Zn^<2+>. The current density in cells with 【greater than or equal】6 nuclei was significantly smaller than that in cells with 【less than or equal】5 nuclei, although the activation rate unaltered. Moreover, the H^+ current was small or negligible in osteoclasts generated in the co-culture of bone marrow cells with a stromal cell line (ST2). Therefore, expression of the H^+ channel or number of active channels could alter during osteoclastogenesis. In most cells with【greater than or equal】6 nuclei activity of NADPH oxidase was low, suggesting a possibility that the activities of the H^+ channel and NADPH oxidase is correlated to the functional states of osteoclasts. This study has provided evidences that expression and activity of the H^+ channels in both microglia and osteoclasts are strongly controlled by their cellular conditions and differentiation process. Less