FGF-1 induces ATP release from spinal astrocytes in culture and opens pannexin and connexin hemichannels

Abstract

Spinal astrocytes are coupled by connexin (Cx) gap junctions and express pannexin 1 (Px1) and purinergic receptors. Fibroblast growth factor 1 (FGF-1), which is released in spinal cord injury, activated spinal astrocytes in culture, induced secretion of ATP, and permeabilized them to relatively large fluorescent tracers [ethidium (Etd) and lucifer yellow (LY)] through "hemichannels" (HCs). HCs can be formed by connexins or pannexins; they can open to extracellular space or can form gap junction (GJ) channels, one HC from each cell. (Pannexins may not form gap junctions in mammalian tissues, but they do in invertebrates). HC types were differentiated pharmacologically and by Px1 knockdown with siRNA and by use of astrocytes from Cx43 knockout mice. Permeabilization was reduced by apyrase (APY), an ATPase, and by P2X 7 receptor antagonists, implicating secretion of ATP and autocrine and/or paracrine action. Increased permeability of cells exposed to FGF-1 or ATP for 2 h was mediated largely by Px1 HCs activated by P2X 7 receptors. After a 7-h treatment, the permeability was mediated by both Cx43 and Px1 HCs. FGF-1 also caused reduction in gap junctional communication. Botulinum neurotoxin A, a blocker of vesicular release, reduced permeabilization when given 30 min before FGF-1 application, but not when given 1 h after FGF-1. We infer that ATP is initially released from vesicles and then it mediates continued release by action on P2X 7 receptors and opening of HCs. These changes in HCs and gap junction channels may promote inflammation and deprive neurons of astrocyte-mediated protection in spinal cord trauma and neurodegenerative disease.astroglia | growth factor | connexon | pannexon | neurodegeneration

Phenotypically aberrant astrocytes that promote motoneuron damage in a model of inherited amyotrophic lateral sclerosis

“…Cx43 also can form hemichannels opened to the extracellular space in inflammatory astrocytes (34,35), which can release extracellular ATP (34,36). Thus, the high levels of Cx43 in AbA cells may explain their potential to trigger glial activation and excitotoxic degeneration of motoneurons (37).…”

Pannexin-1-mediated ATP release from area CA3 drives mGlu5-dependent neuronal oscillations

“…Given the widespread distribution of connexin and pannexin-1 (Panx1) hemichannels on neurones and astrocytes (Cisneros-Mejorado et al, 2014;De Bock et al, 2014) and the strong evidence for a contribution of connexin and pannexin-1 hemichannel-mediated ATP release during neuronal and astrocytic activity (Garre et al, 2010;Santiago et al, 2011;Stout et al, 2002;Suadicani et al, 2012), we decided to test the hypothesis that GI mGluR-evoked ATP release occurs via hemichannels.…”

Intercellular Ca2+Waves: Mechanisms and Function

“…Diffusive ATP release has been suggested to occur via a maxi-anion channel of unknown identity (301), by hemichannels composed of various connexin isoforms (including Cx26, Cx30, Cx32, Cx36, and Cx43) (7,109,179,318,326,343,374,417) or pannexins (15,162,284,336,397), or by the combined action of these channels (121,212). ATP release via connexin and pannexin hemichannels during ICW propagation has been reported to be Ca 2ϩ dependent (83,86,215).…”