A proton-translocating H+-ATPase is involved in C6 glial pH regulation.
Glial cells extrude acid equivalents to maintain pHi. Although four mechanisms have been described so far, pHi-control under physiological conditions is still not sufficiently explained. We therefore investigated whether a H+-translocating ATPase is involved in glial pHi homeostasis using an established glial cell line (C6 glioma). In the absence of bicarbonate, the inhibition of H+-ATPases by NEM led to a pHi decrease. The application of a more specific inhibitor (NBD-Cl) showed that the H+-ATPase involved is of the vacuolar type. Inhibition went along with delayed cell swelling. Together with the fact that glial acidification was far more pronounced in Na+-free media, this may serve as evidence for a secondary activation of Na+/H+-exchange once an activation setpoint is reached, which in turn causes secondary swelling from Na+-uptake. Stimulation of Na+/H+-exchange by PMA can increase the setpoint. pHi-recovery after an acid load was blocked by the inhibition of v-type H+-ATPase, if pHi did not reach 6.6 during the acid load. The inhibition of Na+/H+-exchange by amiloride inhibited recovery only if acidification was below the threshold. Finally, in bicarbonate-free media a v-type H+-ATPase contributes to pH-regulation in glial cells, especially during pH-homeostasis at physiological conditions, while Na+/H+-exchange gains significance during severe acid loads.
Volk
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Institute for Neurosurgical Pathophysiology, Johannes Gutenberg-University Mainz, 55101 Mainz, Germany.
Albert
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Kempski
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D000143:Acids / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D048429:Cell Size; D003470:Culture Media / Q000378:metabolism; D005910:Glioma / Q000201:enzymology* / Q000378:metabolism / Q000473:pathology*; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid / Q000201:enzymology / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D011522:Protons; D051381:Rats; D014407:Tumor Cells, Cultured
D000143:Acids; D003470:Culture Media; D011522:Protons; D006180:Proton-Translocating ATPases