Inhibition of regulatory volume decrease in swollen rat primary astrocyte cultures by methylmercury is due to increased amiloride-sensitive Na + uptake

Abstract

Primary astrocyte cultures from neonatal rats were swollen by exposure to hypotonic buffer with and without 10 μM 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 μM 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.