SCHWANN-CELLS EXHIBIT P-2Y PURINERGIC RECEPTORS THAT REGULATE INTRACELLULAR CALCIUM AND ARE UP-REGULATED BY CYCLIC-AMP ANALOGS

Schwann cells establish close contact with axons during development, a nd this is maintained throughout life. Signaling by neurotransmitters may play an important role in Schwann cell-axon interaction. Schwann c ells were examined for the presence of neuroligand receptors that are linked to increases in levels of cytoplasmic calcium. Schwann cell cul tures were prepared from neonatal rat sciatic nerve and, after 0.25, 1 , 4, 7, and 14 days in vitro (DIV), loaded with the calcium indicator dye fura 2-AM. The influence of neuroligands on the cytosolic free cal cium concentration ([Ca2+](i)) was then examined at each time point us ing a video-based imaging system. Approximately 80-95% of all freshly isolated Schwann cells responded to 10 mu M ATP with a three-fold rise in [Ca2+](i). Bradykinin, glutamate, and histamine had no or only par tial and inconsistent responses. The ATP-induced calcium response disa ppeared within 4 DIV. Culturing cells in the presence of cyclic AMP (c AMP) analogues (which induce proliferation and differentiation in vitr o) restored the ability of Schwann cells to respond to ATP with increa sed [Ca2+](i). In the presence of cAMP analogues the extent of recover y of ATP responsiveness was dependent on serum concentration. Fifty to ninety percent of cells regained calcium responsiveness to ATP when g rown in medium containing cAMP analogues and 1% serum. These cells als o exhibited immunoreactive to P-o antibody, characteristic of the myel inating lineage. In contrast, only 15-30% of the Schwann cells regaine d calcium responsiveness when grown in medium containing cAMP analogue s and 10% serum. Under these conditions all Schwann cells exhibited im munoreactivity to antibodies against nerve growth factor receptor, cha racteristic of the nonmyelinating lineage, although some also containe d galactocerebroside immunoreactivity. The correlation between the rec overy of the ATP response and the recovery of stage-specific markers s uggests that Schwann cell ATP receptor expression may be a development al process, preferentially associated with Schwann cells moving toward the myelinating lineage.