Dissociation of the Stellate Morphology from Intracellular Cyclic AMP Levels in Cultured Rat Brain Astroglial Cells: Effects of Ganglioside GMland Lysophosphatidylserine

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Abstract
Secondary microcultures of newborn rat cerebrum astroglial (AG) cells, maintained in a serum-free, chemically defined medium, were treated with various agents known to elevate intracellular cyclic AMP (cAMP) levels. Earlier studies had shown these drugs to induce a process-bearing (stellate) morphology in the AG cells, a response that was antagonized by the presence of gangliosides. One millimolar dibutyryl cyclic AMP (dBcAMP), 10 .mu.M forskolin, 12 nM cholera toxin, and 30 .mu.M isoproterenol all raised intracellular cAMP levels, from basal values of 3 pmol/106 cells to 30-30,000 pmol/106 cells, depending on the agent tested. dBdcAMP caused the greatest elevation, and forskolin the least. The timing and/or the level of the AMP response did not precisely correlate with those of the stellation response. Values of ED50 with the four agents, as determined for the cAMP response, were always higher than stellation ED50 values in all treatments, and ED50 did not correlate with the maximal levels of cyclic AMP induced by the four agents. The capacity of ganglioside GM1 to block the stellation response to the four agents was not accompanied by a similar capacity to block the cAMP responses. Lysophosphatidylserine (lysoPS) had the capacity to induce AG cell stellation as well, without altering the basal level of cAMP. Both lysoPS and gangliosides, therefore, may act directly on the cellular machinery underlying the stellation response without involving changes in intracellular AMP.