POTASSIUM AND TAURINE RELEASE ARE HIGHLY CORRELATED WITH REGULATORY VOLUME DECREASE IN NEONATAL PRIMARY RAT ASTROCYTE CULTURES

Neonatal rat primary astrocyte cultures were swollen by exposure to hy potonic buffer. Using an electrical impedance method for determination of cell volume coupled with on-line measurements of efflux of radioac tive ions or amino acids, we have investigated the role of K+ (using R b-86), taurine, and D-aspartate (an analogue of glutamate) in regulato ry volume decrease (RVD). Addition of 1 mM quinine, 10 mu M nimodipine , 100 mu M BAPTA-AM, 10 mu M trifluoperazine, or a calcium-free buffer significantly (p < 0.0001) inhibited RVD. This was accompanied by inh ibition of Rb-86 release but an increase in D-[H-3]-aspartate release, which was proportional to the degree to which RVD was inhibited. Thes e results support a regulatory role for calcium in RVD and show that i nhibition of calcium entry from the extracellular fluid, intracellular calcium sequestration, inhibition of calcium-activated K+ channels, a nd inhibition of calmodulin all inhibit RVD. Because D-[H-3]aspartate efflux profiles increase as RVD is inhibited, it is unlikely that D-as partate release is a main determinant of RVD. In contrast, [H-3]taurin e release was increased by 1 mM quinine and inhibited by 10 mu M trifl uoperazine. The net release of K+ and taurine is highly correlated wit h the degree of RVD, implicating a regulatory role for both K+ and tau rine release in RVD.