Choline acetyltransferase activity of spinal cord cell cultures increased by co-culture with muscle and by muscle-conditioned medium

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Abstract
Activity of the enzyme choline acetyltransferase (CAT), which mediates the synthesis of the neurotransmitter, acetylcholine, was increased up to 20-fold in [mouse] spinal cord (SC) cells grown in culture with muscle cells for 2 wk. This increase was directly related to the duration of co-culture and to the cell density of both the SC and muscle involved and was not affected by the presence of the acetylcholine receptor blocking agent, .alpha.-bungarotoxin. Glutamic acid decarboxylase (GAD) activity was often markedly decreased in SC-muscle cultures while the activities of acetylcholinesterase and several other enzymes were little changed. Increased CAT activity was also observed when SC cultures were maintained in medium which had been conditioned by muscle cells or by undifferentiated cells from embryonic muscle. Muscle-conditioned medium (CM) did not affect the activities of SC cell GAD or acetylcholinesterase. Dilution or concentration of the CM directly affected its ability to increase SC CAT activity, as did the duration and timing of exposure of the SC cells to the CM. The medium could be conditioned by muscle cells in the presence or the absence of serum, and remained effective after dialysis or heating to 58.degree. C. Membrane filtration data were consistent with the conclusion that the active material(s) in CM had a MW in excess of 50,000 daltons. The large MW material released by muscle cells is apparently capable of producing a specific increase in CAT activity of SC cells.