Potentiation of a voltage-gated proton current in acidosis-induced swelling of rat microglia.
Microglia are equipped with a strong proton (H(+)) extrusion pathway, a voltage-gated H(+) channel, probably to compensate for the large amount of H(+) generated during phagocytosis; however, little is known about how this channel is regulated in pathological states. Because neural damage is often associated with intracellular and extracellular acidosis, we examined the regulatory mechanisms of the H(+) current of rat spinal microglia in acidic environments. More than 90% of round/amoeboid microglia expressed the H(+) current, which was characterized by slow activation kinetics, dependencies on both intracellular and extracellular pH, and blockage by Zn(2+). Extracellular lactoacidosis, pH 6.8, induced intracellular acidification and cell swelling. Cell swelling was also induced by intracellular dialysis with acidic pipette solutions, pH 5.5-6.8, at normal extracellular pH 7.3 in the presence of Na(+). The H(+) currents were increased in association with cell swelling as shown by shifts 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 nonhydrolytic actions of intracellular ATP and were inhibited by agents affecting actin filaments (phalloidin and cytochalasin D). The H(+) current was also potentiated by swelling caused by hypotonic stress. These findings suggest that the H(+) channel of microglia can be potentiated via cell swelling induced by intracellular acidification. This potentiation might operate as a negative feedback mechanism to protect microglia from cytotoxic acidification and hence acidosis-induced swelling in pathological states of the CNS.
Morihata
H
H
Department of Physiology, Osaka City University Medical School, Abeno-ku, Osaka 545-8585, Japan.
Nakamura
F
F
Tsutada
T
T
Kuno
M
M
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000138:Acidosis / Q000378:metabolism*; D000143:Acids / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism; D000468:Alkalies / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D018118:Chloride Channels / Q000037:antagonists & inhibitors; D002712:Chlorides / Q000494:pharmacology; D015638:Cytochalasin D / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007038:Hypotonic Solutions / Q000494:pharmacology; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D019344:Lactic Acid / Q000378:metabolism / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D017628:Microglia / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology*; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010590:Phalloidine / Q000494:pharmacology; D017494:Proton Pumps / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors; D011522:Protons; D051381:Rats; D017208:Rats, Wistar; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors; D025262:Vacuolar Proton-Translocating ATPases; D017967:Zinc Compounds / Q000494:pharmacology
D000143:Acids; D000468:Alkalies; D018118:Chloride Channels; D002712:Chlorides; D007038:Hypotonic Solutions; D019384:Nucleic Acid Synthesis Inhibitors; D017494:Proton Pumps; D011522:Protons; D017923:Sodium-Hydrogen Exchangers; D017967:Zinc Compounds; D010590:Phalloidine; D015638:Cytochalasin D; D019344:Lactic Acid; C016837:zinc chloride; D000255:Adenosine Triphosphate; D025262:Vacuolar Proton-Translocating ATPases; D006180:Proton-Translocating ATPases; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid