Norepinephrine-induced calcium mobilization in C6 glioma cells

To investigate the mechanism underlying the norepinephrine-induced elevation in intracellular calcium concentration ([Ca2+]i) in C6 glioma cells. Measurement of [Ca2+]i was carried out using the dual-wavelength fluorescence method with fura-2 as the indicator. Norepinephrine was found to induce concentration-dependent increases in [Ca2+ ]i through alpha1-adrenoreceptors. The [Ca2+]i elevations were extracellular-calcium independent and not influenced by the treatment of pertussis toxin. Pretreatments with either U73122 or thapsigargin abolished the subsequent cellular calcium responses to norepinephrine. Preincubation with phorbol 12-myristate 13-acetate (PMA) significantly reduce d the [Ca2+]i elevations, while protein kinase C inhibitors Ro31-8220 or GF-109203X completely blocked the inhibitory action of PMA. However, drugs either activating or inhibiting the function of protein kinase A had no effect on the [Ca2+]i elevations. Norepinephrine induces calcium mobilization from internal stores by activation of phospholipase C in C6 cells. The [Ca2+]i elevation is negatively regulated by the activation of protein kinase C.