[3H]-myo-inositol uptake in rat cortical slices. Identification of Na+-dependent and Na+-independent systems

[3H]-myo-Inositol (MI) uptake was measured in vitro using chopped rat cerebral cortical tissue. The uptake and accumulation of MI were linearly proportional to the amount of protein (0.1 to 4.0 mg) in the incubation medium. The uptake was also linear vs time for the first 20 min of incubation. When the uptake was observed at various substrate concentrations, it was found to be unsaturable up to a concentration of 0.78 M. Decreasing the concentration of NaCl or increasing the concentration of KCl in the incubation medium resulted in inhibition of the uptake and accumulation of MI. Inhibition of MI uptake was also produced by veratrine, ouabain and A23187 which alter the ionic gradients across the neuronal membranes. Inhibition of oxidative metabolism with dinitrophenol did not alter MI uptake. Sodium-independent uptake appeared to be the same as that which occurred at 0 degree. Sodium-independent uptake was still present in water-lysed homogenates and was inhibited by relatively high concentrations of ethanol. Thus, it appears that approximately one-half of the [3H]inositol uptake and accumulation in chopped rat cerebral cortex occurs by a sodium-dependent mechanism that can be altered by drugs which change the sodium gradient and the remaining occurs by a sodium-independent mechanism that can be altered by ethanol which is known to change membrane fluidity of neuronal membranes.