Guinea pig gallbladder and pancreas possess identical CCK-A receptor subtypes: receptor cloning and expression

Abstract

Cholecystokinin (CCK) receptors mediate pancreatic acinar secretion and gallbladder contraction. Pharmacological and functional studies in pancreas and gallbladder demonstrate a CCK-A receptor subtype in both tissues. However, some pharmacological studies and affinity cross-linking studies of CCK receptors on pancreatic acini and gallbladder suggest that these two tissues possess two different subtypes of the CCK-A receptor. We cloned these receptors in guinea pig using a cDNA clone of the CCK-A receptor from rat pancreas. The guinea pig gallbladder CCK-A receptor was cloned by hybridization screening of a gallbladder cDNA library using a cDNA probe from the rat CCK-A receptor coding region. The guinea pig pancreas CCK-A receptor cDNA was cloned via the polymerase chain reaction using primers corresponding to the guinea pig gallbladder CCK-A receptor 5'- and 3'-noncoding regions. CCK-A receptor clones from guinea pig pancreas and gallbladder had identical nucleotide sequences, which were 80% homologous to the rat CCK-A receptor cDNA sequence. The deduced amino acid sequence from guinea pig CCK-A receptors was 89% homologous to the rat CCK-A receptor sequence. Dose-inhibition binding studies of transiently expressed receptors by CCK agonists and antagonists exhibited a CCK-A receptor pharmacologically similar to the rat CCK-A receptor. These studies indicate that the CCK-A receptors in guinea pig pancreas and gallbladder are identical and do not support previous proposals that they may represent different receptor subtypes.