Vasoactive intestinal peptide as a regulator of exocrine function and as a possible factor in cystic fibrosis

Molecular cloning and functional characterization of a human liver vasoactive intestinal peptide receptor

We have isolated a cDNA from a human liver library which is 2349 base pairs in length and encodes a near-full length seven transmembrane receptor (432 amino acids), 85% homologous to the amino acid sequence for the rat vasoactive intestinal peptide (VIP) receptor. Northern blot analysis identifies a major species at 3.3 kb in lung, and to a lesser extent in brain, heart and liver. In order to confirm the identity of this human clone, double-stranded oligonucleotides encoding the signal peptide of the rat VIP receptor were constructed by polymerase chain reaction and attached to the 5' end of the human clone. COS cells transiently transfected with this human VIP receptor chimera, express a single binding site for 125I-VIP with a Kd of 9.2 +/- 2 nM. Related peptides displace 125I-VIP with a relative potency of VIP = PACAP > helodermin >> PHM > secretin, which is similar to the binding profile seen in human tissues. This human chimeric receptor is functionally coupled to the stimulation of adenylyl cyclase in transfected COS cells, as evidenced by a dose-dependent increase in intracellular cAMP accumulation. These studies indicate that this cDNA encodes a human liver VIP receptor which is functionally coupled to the activation of adenylyl cyclase.

Measurement of intracellular mediators in enterocytes isolated from jejunal biopsy specimens of control and cystic fibrosis patients

A method that maximises the yield of viable enterocytes has been developed for the isolation of enterocytes from human jejunal biopsy specimens. These enterocytes have been used to study the values of intracellular free calcium and the rises in adenosine 3'5'-cyclic monophosphate (cAMP) induced by secretagogues in normal and cystic fibrosis cells. Basal intracellular free calcium of cystic fibrosis enterocytes, measured fluorimetrically with fura-2, was within the range of the basal intracellular free calcium of non-cystic fibrosis enterocytes (cystic fibrosis 263 nmol/l; non-cystic fibrosis 287 nmol/l). Changes in intracellular free calcium were observed after exposure to ionomycin: a 100 nmol/l solution induced a 2.5 fold increase in intracellular free calcium in the cystic fibrosis enterocytes and a 2.2 fold increase in the intracellular free calcium concentration of the non-cystic fibrosis enterocytes. Basal cAMP values were not significantly different between cystic fibrosis and non-cystic fibrosis enterocytes (cystic fibrosis 575 fmol/100,000 cells; non-cystic fibrosis 716 fmol/100,000 cells, p greater than 0.05) and the enterocyte cAMP value increased in response to stimulation with prostaglandin E2 (7 mumol/l) (cystic fibrosis 2.2 fold increase over basal, p less than 0.05; non-cystic fibrosis 1.9 fold stimulation over basal, p less than 0.05) and vasoactive intestinal polypeptide (100 nmol/l) (cystic fibrosis 7.1 fold increase over basal, p less than 0.05; non-cystic fibrosis 5.8 fold increase over basal, p less than 0.05). There was no significant difference in the magnitude of the response between cystic fibrosis and non-cystic fibrosis enterocytes (p greater than 0.05). These results indicate that the cystic fibrosis defect in the small intestine, as in other affected epithelia, seems to be distal to the production of second messengers. The small intestine is therefore an appropriate model in which to study the biochemical defect in cystic fibrosis.