The poorly differentiated human gastric carcinoma cell line MKN-45 possesses histamine H2 receptors which are homologously desensitized by histamine. In order to clone the cDNA of a receptor kinase specific for H2 receptors, we performed RT-PCR at a low annealing temperature using oligo-DNA primers bearing the conserved sequences of the kinase domain of the G protein-coupled receptor kinase (GRK) family. However, we were able to isolate only cDNAs for β-adrenergic receptor kinase 1 (βARK1) and GRK6. Interestingly, treatment of MKN-45 cells with βARK1 antisense phosphorothioate oligo-DNA (PON) resulted in significant loss of desensitization of H2 receptors by histamine, whereas GRK6 antisense PON had no effect. Thus, βARK1 appears to be involved in the homologous desensitization of H2 receptors in MKN-45 ce