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 CCKB receptors. However, recent studies suggest the expression of an additional CCK receptor subtype distinct from CCKB receptors in this tissue. This study was designed to distinguish between CCKA and CCKB 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 P-32 random primed labeled cDNA probes from the recently cloned rat CCKA and CCKB receptor coding regions. In addition to clones representing the CCKB subtype, clones of CCKA receptor subtype, but no additional CCK receptor subtypes, could be identified. All isolated clones displayed highly homologous nucleotide sequences in comparison to previously characterized CCKA and CCKB 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 CCKA and CCKB receptors exist in stomach smooth muscle. (C) 1997 Elsevier Science B.V.