Homologous and heterologous desensitization of histamine H1‐and ATP‐receptors in the smooth muscle cell line, DDT1MF‐2: the role of protein kinase C

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Abstract
1 The possible role of protein kinase C (PKC) in homologous and heterologous desensitization of histamine H1- and ATP-receptors has been studied in monolayers of cultured vas deferens smooth muscle cells (DDT1MF-2). Cells were loaded with the calcium-sensitive fluorescent dye fura-2 and increases in intracellular free Ca2+ concentration ([Ca2+]i) monitored in response to histamine H1- or ATP-receptor activation. 2 Histamine and ATP stimulated the release of Ca2+ from intracellular Ca2+ stores and Ca2+ influx across the plasma membrane. Activation of PKC with the phorbol ester β-phorbol-12,13 dibutyrate (PDBu; 1 μm) attenuated histamine (100 μm) and ATP (10 μm)-induced release of intracellular Ca2+ and Ca2+ influx. 3 The selective PKC inhibitor, Ro 31–8220 (10 μm), reversed the PDBu-induced attenuation of histamine (100 μm)-stimulated Ca2+ responses. 4 Histamine H1- and ATP-receptors are readily susceptible to homologous desensitization since short-term exposure to histamine or ATP (450 s) attenuated the Ca2+ responses elicited by a second application of the same agonist. Furthermore, H1-receptor activation-induced heterologous desensitization of ATP stimulated Ca2+ responses and vice versa. 5 Homologous and heterologous desensitization of histamine and ATP Ca2+ responses still occurred in the presence of the PKC inhibitor, Ro 31–8220 (10 μm). 6 These data suggest that PKC activation can attenuate histamine H1- and ATP-receptor mediated Ca2+ responses. However, based on our experimental data, PKC-independent mechanisms appear to be involved in the homologous and heterologous desensitization of histamine H1- and ATP-receptor mediated Ca2+ responses in DDT1MF-2 cells.