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 hypotonic buffer. Using an electrical impedance method for determination of cell volume coupled with on-line measurements of efflux of radioactive ions or amino acids, we have investigated the role of K+ (using 86Rb), taurine, and D-aspartate (an analogue of glutamate) in regulatory volume decrease (RVD). Addition of 1 mM quinine, 10 microM nimodipine, 100 microM BAPTA-AM, 10 microM trifluoperazine, or a calcium-free buffer significantly (p < 0.0001) inhibited RVD. This was accompanied by inhibition of 86Rb release but an increase in D-[3H]-aspartate release, which was proportional to the degree to which RVD was inhibited. These results support a regulatory role for calcium in RVD and show that inhibition of calcium entry from the extracellular fluid, intracellular calcium sequestration, inhibition of calcium-activated K+ channels, and inhibition of calmodulin all inhibit RVD. Because D-[3H]aspartate efflux profiles increase as RVD is inhibited, it is unlikely that D-aspartate release is a main determinant of RVD. In contrast, [3H]taurine release was increased by 1 mM quinine and inhibited by 10 microM trifluoperazine. The net release of K+ and taurine is highly correlated with the degree of RVD, implicating a regulatory role for both K+ and taurine release in RVD.

The osmotic permeability of isolated calf pulmonary artery endothelial cells.

Osmotic permeability coefficients, PF, for water in isolated calf pulmonary artery endothelial cells determined over the temperature range 41 to 20 degrees C are 311.10(-5) cm.s-1 at 37 degrees C and 159.10(-5) cm.s-1 at 20 degrees C. The value at 37 degrees C is close to that reported earlier for the diffusional permeability coefficient, PD. The PF/PD ratio is 1.0 at 37 degrees C. The PF values are within the range of values extrapolated for filtration permeability in pulmonary endothelium. The temperature dependence expressed as the activation energy is 7.2 kcal.mol-1. The product of hydraulic conductivity, Lp (or PF) and of viscosity changes in water is not constant from 37 to 20 degrees C. These results can be interpreted to indicate a similar pathway for water whether under diffusional or osmotic gradients.