P-2-PURINERGIC RECEPTORS REGULATE PHOSPHOLIPASE-C AND ADENYLATE-CYCLASE ACTIVITIES IN IMMORTALIZED SCHWANN-CELLS

Schwann cells play an important role in both the development and regen eration of peripheral nerves. Proliferation and differentiation of Sch wann cells are critically dependent on changes in the levels of cAMP, ATP is a fast excitatory transmitter in the peripheral nervous system, inducing depolarization of the vagus nerve through occupancy of P-2-p urinergic receptors. In the present study we demonstrate that extracel lular ATP stimulates phospholipase C and inhibits adenylate cyclase ac tivities in cultured Schwann cells. Addition of ATP inhibited, in a co ncentration-dependent manner, forskolin- or isoprenaline-stimulated ad enylate cyclase activity. The rank order of potency corresponding to d ifferent purinergic receptor agonists was 2-methylthio-ATP > ATP = ADP greater than or equal to adenosine 5'-[gamma-thio]triphosphate (ATP[S ]) > UTP, consistent with the involvement of a P-2y subtype. Adenosine and adenosine 5'-[alpha,beta-methylene]-triphosphate (pp[CH(2)pA) wer e ineffective. Preincubation with pertussis toxin completely blocked t his inhibitory effect. When Schwann cells were pre-labelled with myo-[ H-3]inositol and incubated in Hanks balanced salt solution containing Ca2+ and Mg2+, addition of ATP[S] resulted in a concentration-dependen t increase in the release of InsP with a concomitant increase in intra cellular free [Ca2+] ([Ca2+](i)). Under these conditions, the effects of both ATP and UTP were of lower magnitude. Removal of Ca2+ and Mg2from the assay medium resulted in a significant increase in the effect s of ATP[S], ATP and UTP. The decreased response observed in the prese nce of both bivalent cations (1.2 mM Ca2+ and 1 mMMg(2+)) could not be explained either by increased degradation of ATP by Ca2+/Mg2+-depende nt nucleotidases or by cation influx. The rank order of potency for th e effects of agonists on phospholipase C activity was ATP[S] = adenosi ne 5'-[gamma-imido]triphosphate > ATP = UTP > ADP, indicating the invo lvement of a P-2u receptor subtype in this response. Adenosine, AMP an d pp[CH2]pA were ineffective. These results demonstrate that immortali zed Schwann cells express P-2u and P-2y purinoceptors, which are coupl ed to stimulation of phospholipase C and inhibition of adenylate cycla se, respectively. Our observations unveil signal-transduction pathways that may be used by ATP to regulate proliferation and differentiation of Schwann cells, and ultimately to influence nerve homoeostasis.