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.