Acid-inducible proton influx currents in the plasma membrane of murine osteoclast-like cells

Abstract

Acidification of the resorption pits, which is essential for dissolving bone, is produced by secretion of protons through vacuolar H(+)-ATPases in the plasma membrane of bone-resorbing cells, osteoclasts. Consequently, osteoclasts face highly acidic extracellular environments, where the pH gradient across the plasma membrane could generate a force driving protons into the cells. Proton influx mechanisms during the acid exposure are largely unknown, however. In this study, we investigated extracellular-acid-inducible proton influx currents in osteoclast-like cells derived from a macrophage cell line (RAW264). Decreasing extracellular pH to <5.5 induced non-ohmic inward currents. The reversal potentials depended on the pH gradients across the membrane and were independent of concentrations of Na(+), Cl(-), and HCO3 (-), suggesting that they were carried largely by protons. The acid-inducible proton influx currents were not inhibited by amiloride, a widely used blocker for cation channels/transporters, or by 4,4'-diisothiocyanato-2,2'-stilbenesulfonate(DIDS) which blocks anion channels/transporters. Additionally, the currents were not significantly affected by V-ATPase inhibitors, bafilomycin A1 and N,N'-dicyclohexylcarbodiimide. Extracellular Ca(2+) (10 mM) did not affect the currents, but 1 mM ZnCl2 decreased the currents partially. The intracellular pH in the vicinity of the plasma membrane was dropped by the acid-inducible H(+) influx currents, which caused overshoot of the voltage-gated H(+) channels after removal of acids. The H(+) influx currents were smaller in undifferentiated, mononuclear RAW cells and were negligible in COS7 cells. These data suggest that the acid-inducible H(+) influx (H(+) leak) pathway may be an additional mechanism modifying the pH environments of osteoclasts upon exposure to strong acids.

Elevated resting H+ current in the R1239H type 1 hypokalaemic periodic paralysis mutated Ca2+ channel

“…; Kuno et al . ). In particular, the proton current here described displayed an inward rectification for voltages lower than −40 mV, which also distinguishes it from the current flowing through voltage‐activated proton channels (Bernheim et al .…”

Implications of Salinity and Acidic Environments on Fitness and Oxidative Stress Parameters in Early Developing Seahorses Hippocampus reidi

“…This assumption agrees with the increase in growth induced at pH 6.3 in turbot Psetta maxima when compared to upper pH levels tested (up to pH 8.8) [ 115 ]. The good results obtained in the oxidative status and growth of juveniles raised in SW at pH 6.5 are related to acidic chemistry, since H + is involved in aerobic and non-aerobic energy metabolism, affecting mitochondrial proton leak while interacting with metabolites of non-mitochondrial energy generation [ 101 , 102 , 116 ]. This can trigger benefits for cell energy and oxidative status.…”

V-ATPase (Vacuolar ATPase) Activity Required for ABCA1 (ATP-Binding Cassette Protein A1)-Mediated Cholesterol Efflux

“…In our current study, ABCA1 induction in BHK cells did not lead to a decrease in the extracellular pH that we could detect using the Seahorse ECAR assay, perhaps this could be due to lack of sufficient sensitivity of this assay. The lack of detectable extracellular acidification could also be due to a passive diffusion of secreted protons back across the plasma membrane down their electrochemical gradient into the cell, 35 or via an active transporter such as the potassium-proton antiporter. 36 Alternatively, this situation could be similar to what Maxfield observed with the formation of a transiently sealed compartment on the plasma membrane so that the V-ATPase extruded protons did not reach the bulk extracellular medium.…”