Activation of the neurokinin-1 receptor in rat spinal astrocytes induces Ca2+ release from IP3-sensitive Ca2+ stores and extracellular Ca2+ influx through TRPC3

Substance P (SP) plays an important role in pain transmission through the stimulation of the neurokinin (NK) receptors expressed in neurons of the spinal cord and the subsequent increase in the intracellular Ca2+ concentration ([Ca2+](i)) as a result of this stimulation RI cent studies suggest that spinal astrocytes also contribute to SP-related pain transmission through the activation of NK receptors However the mechanisms involved in the SP-stimulated [Ca2+](i) increase by spinal astrocytes are unclear We therefore examined whether (and how) the activation of NK receptors evoked Increase in [Ca2+](i) in rat cultured spinal astrocytes using a Ca2+ imaging assay Both SP and GR73632 (a selective agonist of the NK1 receptor) induced both transient and sustained increases in [Ca2+](i) in a dose-dependent manner The SP-induced increase in [Ca2+](i) was significantly attenuated by CP-96345 (an NK1 receptor antagonist) The GR73632-induced increase in [Ca2+](i) was completely inhibited by pretreatment with U73122 (a phospholipase C inhibitor) or xestospongin C (an inositol 1 4 5-triphosphate (IP3) receptor inhibitor) In the absence of extracellular Ca2+ GR73632 Induced only a transient increase in [Ca2+](i) In addition H89 an inhibitor of protein kinase A (PICA) decreased the GR73682-mediated Ca2+ release from intracellular Ca2+ stores while bisindolylmaleimide I an inhibitor of protein kinase C (PKC) enhanced the GR73632-induced influx of extracellular Ca2+ RT-PCR assays revealed that canonical transient receptor potential (TRPC) 1 2 3 4 and 6 mRNA were expressed in spinal astrocytes Moreover BTP2 (a general TRPC channel inhibitor) or Pyr3 (a TRPC3 inhibitor) markedly blocked the GR73632-induced sustained increase in [Ca2+](i) These findings suggest that the stimulation of the NK-1 receptor in spinal astrocytes induces Ca2+ release from IP3 sensitive intracellular Ca2+ stores which is positively modulated by PICA, and subsequent Ca2+ influx through TRPC3 which is negatively regulated by PKC (C) 2010 Elsevier Ltd All rights reserved