Inhibition of regulatory volume decrease in swollen rat primary astrocyte cultures by methylmercury is due to increased amiloride-sensitive Na+ uptake.
Primary astrocyte cultures from neonatal rats were swollen by exposure to hypotonic buffer with and without 10 microM methylmercury (MeHg). We investigated the effects of MeHg on K+ (using 86Rb), taurine, D-aspartate (a non metabolizable analogue of glutamate) and Na+ fluxes during regulatory volume decrease (RVD), with an electrical impedance method for determination of cell volume, coupled with on-line measurements of efflux of radioactive ions and amino acids. Addition of 10 microM MeHg completely inhibited RVD in swollen astrocytes, increased the uptake of 22Na+, increased 86Rb release, and decreased 3H-taurine release. There was no effect on the rate of release of 3H-D-aspartate from swollen astrocytes. 0.5 mM amiloride completely inhibited MeHg-induced increased Na+ influx during RVD, while 1 mM furosemide had no effect. When Na+ in the hypotonic buffer was replaced with N-methyl-D-glucamine (NMDG), RVD in the presence of MeHg was indistinguishable from controls. These results indicate that MeHg increases cellular permeability to ions such as Na+ and K+, and that an increase in Na+ permeability via Na+/H+ exchange, offsetting K+ loss, is the primary mechanism in its inhibition of RVD in swollen astrocytes.
Vitarella
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Department of Pharmacology and Neuroscience, Albany Medical College, NY, USA.
Kimelberg
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Aschner
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D000584:Amiloride / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D001224:Aspartic Acid / Q000378:metabolism; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D001692:Biological Transport; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology* / Q000502:physiology; D006706:Homeostasis; D007038:Hypotonic Solutions; D007700:Kinetics; D008767:Methylmercury Compounds / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D013654:Taurine / Q000378:metabolism
D007038:Hypotonic Solutions; D008767:Methylmercury Compounds; D013654:Taurine; D001224:Aspartic Acid; D000584:Amiloride; D012964:Sodium; D012413:Rubidium; D011188:Potassium