Characterization of CCK receptors in stomach smooth muscle: evidence for two subtypes

Cholecystokinin (CCK) and related peptides such as gastrin are important regulators of gastric smooth muscle contraction. Several studies have shown that these effects of CCK and gastrin are mediated by CCK(B) receptors. However, recent studies suggest the expression of an additional CCK receptor subtype distinct from CCK(B) receptors in this tissue. This study was designed to distinguish between CCK(A) and CCK(B) receptors on guinea-pig stomach smooth muscle cells and to evaluate these cells for additional receptor subtypes. We cloned these receptors by hybridization screening of a guinea-pig smooth muscle cDNA library using 32P random primed labeled cDNA probes from the recently cloned rat CCK(A) and CCK(B) receptor coding regions. In addition to clones representing the CCK(B) subtype, clones of CCK(A) receptor subtype, but no additional CCK receptor subtypes, could be identified. All isolated clones displayed highly homologous nucleotide sequences in comparison to previously characterized CCK(A) and CCK(B) receptors from different species. The results of cDNA hybridization at different levels of stringency and Southern blot analysis using guinea-pig genomic DNA suggest that it is unlikely that additional CCK receptors despite CCK(A) and CCK(B) receptors exist in stomach smooth muscle.