title: Dopaminergic neurotoxicants cause biphasic inhibition of purinergic calcium signaling in astrocytes.
abstract: Dopaminergic nuclei in the basal ganglia are highly sensitive to damage from oxidative stress, inflammation, and environmental neurotoxins. Disruption of adenosine triphosphate (ATP)-dependent calcium (Ca2+) transients in astrocytes may represent an important target of such stressors that contributes to neuronal injury by disrupting critical Ca2+-dependent trophic functions. We therefore postulated that plasma membrane cation channels might be a common site of inhibition by structurally distinct cationic neurotoxicants that could modulate ATP-induced Ca2+ signals in astrocytes. To test this, we examined the capacity of two dopaminergic neurotoxicants to alter ATP-dependent Ca2+ waves and transients in primary murine striatal astrocytes: MPP+, the active metabolite of 1-methyl 4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and 6-hydroxydopamine (6-OHDA). Both compounds acutely decreased ATP-induced Ca2+ transients and waves in astrocytes and blocked OAG-induced Ca2+ influx at micromolar concentrations, suggesting the transient receptor potential channel, TRPC3, as an acute target. MPP+ inhibited 1-oleoyl-2-acetyl-sn-glycerol (OAG)-induced Ca2+ transients similarly to the TRPC3 antagonist, pyrazole-3, whereas 6-OHDA only partly suppressed OAG-induced transients. RNAi directed against TRPC3 inhibited the ATP-induced transient as well as entry of extracellular Ca2+, which was augmented by MPP+. Whole-cell patch clamp experiments in primary astrocytes and TRPC3-overexpressing cells demonstrated that acute application of MPP+ completely blocked OAG-induced TRPC3 currents, whereas 6-OHDA only partially inhibited OAG currents. These findings indicate that MPP+ and 6-OHDA inhibit ATP-induced Ca2+ signals in astrocytes in part by interfering with purinergic receptor mediated activation of TRPC3, suggesting a novel pathway in glia that could contribute to neurotoxic injury.
authors.affiliation: Center for Environmental Medicine, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Karin M
authors.initials: KM
authors.lastname: Streifel
authors.affiliation: Vascular Physiology Research Group, Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Albert L
authors.initials: AL
authors.lastname: Gonzales
authors.affiliation: Center for Environmental Medicine, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Briana
authors.initials: B
authors.lastname: De Miranda
authors.affiliation: Department of Veterinary Integrative Biosciences, Texas A & M University, College Station, Texas, United States of America.
authors.forename: Rola
authors.initials: R
authors.lastname: Mouneimne
authors.affiliation: Vascular Physiology Research Group, Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Scott
authors.initials: S
authors.lastname: Earley
authors.affiliation: Center for Environmental Medicine, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Ronald
authors.initials: R
authors.lastname: Tjalkens
mesh_terms: D015632:1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001253:Astrocytes / Q000187:drug effects* / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects*; D002460:Cell Line; D003342:Corpus Striatum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015259:Dopamine Agents / Q000494:pharmacology*; D006801:Humans; D051379:Mice; D009498:Neurotoxins / Q000494:pharmacology*; D016627:Oxidopamine / Q000494:pharmacology; D058905:Purinergic Agents / Q000494:pharmacology*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D050052:TRPC Cation Channels / Q000378:metabolism
chemical_list: D015259:Dopamine Agents; D009498:Neurotoxins; D058905:Purinergic Agents; D043562:Receptors, G-Protein-Coupled; D050052:TRPC Cation Channels; C104603:TRPC3 cation channel; D016627:Oxidopamine; D000255:Adenosine Triphosphate; D015632:1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; D002118:Calcium