Cholinergic differentiation of clonal rat pheochromocytoma cells (PC12) induced by factors contained in glioma-conditioned medium: Enhancement of high-affinity choline uptake system and reduction of norepinephrine uptake system

Abstract

The effects of glioma-conditioned medium (GCM) and factors contained in GCM on the neurochemical differentiation of the PC12 clone of rat pheochromocytoma cells were investigated. The results obtained are as follows. The accumulation of choline into PC12 cells proceeded through two uptake systems with high ( K m = 3.20 μM) and low ( K m = 65.2 μM) affinities as revealed by least-squares iterative fitting of a substrate-velocity curve to the data. Culturing of PC12 cells in the presence of GCM led to a 5-fold increase in the V max value of the high-affinity uptake system without affecting the K m of the high-affinity uptake system. Both K m and V max of the low-affinity uptake system were unaffected by the GCM treatment. The high-affinity choline uptake system in both GCM-treated and -untreated PC12 cells was devoid of Na + dependency and showed low sensitivity to hemicholinium-3. The ratio of [ 3H]acetylcholine converted from [ 3H]choline taken up by PC12 cells at 1 μM choline for 1 h was two-fold higher than that by untreated cells. PC12 cells possess a high-affinity norepinephrine uptake system. Culturing of PC12 cells in the presence of GCM led to a decrease in the rate of uptake of 3 μM norepinephrine to 43% of that in control cells. The 40-K and 10-K fractions isolated by gel filtration of GCM had both abilities to enhance the high-affinity choline uptake system and to suppress the high-affinity norepinephrine uptake system. From these observations it was concluded that GCM contains factors which induce the cholinergic neuronal differentiation of PC12 cells.