Phorbol ester-mediated desensitization of histamine Hl receptors on a cultured smooth muscle cell line

The present study was undertaken in order to examine the effect of protein kinase C (PKC) on histamine Hl receptors, (HlR) present on the smooth muscle cell line, DDT1MF-2. [3H]-pyrilamine binding revealed that specific [3H]-pyrilamine binding sites were reduced be pretreatment with 12-O-tetra-decanoylphorbol-13-acetate (TPA), an activator of PKC, but not the Kd. The TPA analogue, 4α phorbol 12,13-didecanoate, which does not activate PKC, failed to induce down-regulation of HlR. TPA-induced down regulation of HlR was inhibited by pretreatment with 1-(5-Isoquinilinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), a PKC inhibitor, in a dose dependent manner. The H-7 analogue, H-8, which is a less potent inhibitor of PKC, but a potent inhibitor of cyclic nucleotide dependent protein kinase, had no effect on HlR. Moreover, treatment with TPA inhibited histamine-induced increases in [Ca2+]/sub i/ in cells loaded with the fluorescent indicator, indo-1. These data suggest that HlR in DDT1MF-2 cells were functionally regulated by PKC