Abstract

Functional subtyping of neurokinin and histamine receptors on the canine proximal colon suggested that different receptors were involved in mediating the neural and non-neural effects on ion transport. If the non-neural effects involved direct stimulation of the transporting epithelial cells, mRNA for specific receptor subtypes should be present in colonic crypt cells. Pharmacological data predicted that RNA from such cells would include mRNAs for neurokinin (NK-1) and histamine (H1 and H2) receptors but not for NK-2 or NK-3 receptors. Using published sequences for the above receptors and reverse-transcription polymerase chain reaction, we have noted that isolated canine colonic crypts had mRNA for NK-1 and NK-2 receptors but not for NK-3 receptors. Messenger RNAs for both H1 and H2 receptors were present. The muscularis mucosa and submucosal plexuses had mRNAs for NK-1, NK-3, H1 and H2 receptors but not for NK-2 receptors. The circular and longitudinal muscles expressed mRNA for all three neurokinin and both histamine receptors. Messenger RNA levels for the alpha-1 isoform of the catalytic subunit of the sodium pump were higher in crypts and lower in muscularis mucosa and muscle preparation. Thus these observations provide further evidence for the existence of different receptor subtypes in the canine colon.