FGF-1 Triggers Pannexin-1 Hemichannel Opening in Spinal Astrocytes of Rodents and Promotes Inflammatory Responses in Acute Spinal Cord Slices

We show here that the growth factor FGF-1 is proinflammatory in the spinal cord and explore the inflammatory mechanisms. FGF-1 applied to rat spinal astrocytes in culture initiates calcium signaling and induces secretion of ATP that within minutes increases membrane permeability to ethidium (Etd(+)) and Ca2+ by activating P2X(7) receptors (P2X(7)Rs) that open pannexin hemichannels (Px1 HCs) that release further ATP; by 7 h treatment, connexin 43 hemichannels (Cx43 HCs) are also opened. In acute mouse spinal cord slices ex vivo, we found that FGF-1 treatment for 1 h increases the percentage of GFAP-positive astrocytes that show enhanced Px1 HC-mediated Etd(+) uptake. This response to FGF-1 was not observed in astrocytes in slices of cerebral cortex. FGF-1-induced dye uptake by astrocytes is prevented by BAPTA-AM or a phospholipase C(PLC) inhibitor. Furthermore, in spinal cord slices, P2X(7)R antagonists (BBG and A740003) and Px1 HC blockers ((10)Panx1 and carbenoxolone) prevent the increase in Etd(+) uptake by astrocytes, whereas Gap19, a selective Cx43HC blocker, has no effect on dye uptake at this time. Microglia are not required for the increase in Etd(+) uptake by astrocytes induced by FGF-1, although they are activated by FGF-1 treatment. The morphological signs of microglia activation are inhibited by P2X(7)R antagonists and (10)Panx1 and are associated with elevated levels of proinflammatory cytokines in cord slices treated with FGF-1. The FGF-1 initiated cascade may play an important role in spinal cord inflammation in vivo.