Adaptive Changes in the Heterologous Desensitization Event after Histamine Activates its H1 Receptor in C6 Glioma Cells

Abstract

The possible role of protein kinase C (PKC) linked to the heterologous desensitization of histamine H1 and other receptors was investigated. Receptor activators, such as ATP, PAF, and bradykinin, or calcium ionophore A-23187 were employed for study in the cultured C6 glioma cells. Cells were loaded with the calcium-sensitive fluorescent dye fura-2 and increases in intracellular free calcium concentration ([Ca^(2+)](subscript i)) were monitored in response to histamine H1 or other receptor activations. Histamine stimulated the release of Ca^(2+) from intracellular Ca^(2+) stores and Ca^(2+) influx across the plasma membrane. Under pre-activation of PKC with the phorbol ester β-phorbol-12, 13 dibutyrate (PMA, 10 nM), it caused an attenuation of histamine (100 μM), ATP (100 μM), PAF (1 μM), or bradykinin (1 μM)-induced [Ca^(2+)](subscript i) increase. The relative potency order of attenuation was histamine (92.2%) ＞ ATP (83.3%) ＞ PAF (50.2%) ＞ bradykinin (48.0%) ＞ A23187 (0.2%) in the calcium movement. Similar trend was observed in the histamine pretreatment case among these agents. In this study, 100 nM A23187 (its action is independent of protein kinase C activity), was not found to have a heterologous desensitization in histamine- or PMA-induced calcium movement. Hence PKC activator PMA, and its inhibitor staurosporine could cause significant effects on this heterologous desensitization event. It is proposed that PKC phosphorylating the substrate proteins plays an important role in this shortterm desensitization of histamine acting on histamine H1 receptors in the C6 glioma cells. Our data support the claim that PKC phosphorylates its substrate of the inositol 1, 4, 5-trisphosphate receptor (IP3R) and decreases the mobilization of [Ca^(2+)](subscript i) in these cells, which linked to homologous or/and heterologous desensitization.