Endothelin-activated calcium signaling in enteric glia derived from neonatal guinea pig

The ability of guinea pig enteric glia to respond to endothelins was examined using fura 2-based digital microscopy in glial cells derived from guinea pig taenia coli. Each isoform of endothelin (ET-1, ET-2, ET-3) evoked dose-dependent and equipotent increases in intracellular Ca2+ concentration ([Ca2+]i) and in percentage of cells responding, 4alaEt-1, an ETB receptor agonist, elicited similar [Ca2+]i increments. BQ-788, an ETB antagonist, inhibited [Ca2+]i responses to endothelin. Preincubation of glia with U-73122 a phospholipase C inhibitor, abolished the [Ca2+]i response to ET-3 exposure. Thapsigargin also eliminated ET-3-evoked Ca2+ signaling. The inositol 1,4,5-trisphosphate (IP3) receptor antagonist heparin, introduced into glial cells by radio frequency electroporation, blocked [Ca2+]i responses to ET-3 (100 nM) in 63% of glia. Sustained elevation in [Ca2+]i was abolished by removal of Ca2+ from the buffer and inhibited 85. -3% by Ni2+ (1 mM). Preincubation of glia with 100 nM phorbol 12-myristate 13-acetate (24 h) also inhibited sustained increments in [Ca2+]i by 87%. The presence of IP3 receptors in enteric glia was confirmed by immunofluorescent confocal microscopy.