Receptor-mediated desensitisation of histamine H1 receptor-stimulated inositol phosphate production and calcium mobilisation in GT1-7 neuronal cells is independent of protein kinase C.

GT1-7 cells, a clonal line derived from specific tumours of gonadotropin-releasing hormone-secreting neurons from mouse hypothalamus, were used as a model system to investigate the cellular mechanisms underlying the histamine H1 receptor-mediated desensitisation. GT1-7 cells contain H1 receptors, acute stimulation of which leads to the desensitisation of histamine-mediated calcium mobilisation and is manifest as a concurrent reduction in both the magnitude of the calcium transient and of the sustained phase. Acute pretreatment of the cells with the phorbol ester, phorbol 12-myristate 13-acetate, can also ablate the histamine-stimulated calcium mobilisation. In addition, acute H1-receptor stimulation and acute phorbol ester treatment result in the attenuation of histamine-mediated inositol phosphate production. Receptor desensitisation resulting from acute stimulation with histamine is not affected by inhibiting protein kinase C (PKC) activity with Ro 31-7549 or staurosporine. In contrast, the desensitisation of H1-receptor responses induced by direct activation of protein kinase C is preventable by PKC inhibitors. Thus, these results imply that a PKC-dependent mechanism and PKC-independent mechanism are involved in the H1-receptor desensitisation cascade in GT1-7 cells and do not support the involvement of PKC in the receptor-mediated desensitisation of H1 receptor-stimulated calcium and inositol phosphate responses.