Human colonic epithelial cells express galanin-1 receptors, which when activated cause Cl- secretion.

Galanin is a peptide hormone widely expressed in the central nervous system and gastrointestinal (GI) tract. Within the GI tract galanin is present in enteric nerve terminals where it is known to modulate intestinal motility by altering smooth muscle contraction. Recent studies also show that galanin can alter intestinal short-circuit current (Isc) but with differing results observed in rats, rabbits, guinea pigs, and pigs. In contrast, nothing is known about the ability of galanin to alter ion transport in human intestinal epithelial tissues. By RT-PCR, we determined that these tissues express only the galanin-1 receptor (Gal1-R) subtype. To evaluate Gal1-R pharmacology and physiology, we studied T84 cells. Gal1-R expressed by these cells bound galanin rapidly (half time 1-2 min) and with high affinity (inhibitor constant 0.7 +/- 0.2 nM). T84 cells were then studied in a modified Ussing chamber and alterations in Isc, a measure of all ion movement across the tissue, were determined. Maximal increases in Isc were observed in a concentration-dependent manner around 2 min after stimulation with peptide, with 1 microM galanin causing Isc to rise more than eightfold and return to baseline occurring within 10 min. The increase in galanin-induced Isc was shown by 125I efflux studies to be due to Cl- secretion, which occurred independently of alterations in cAMP and phospholipase C. Rather, Cl- secretion is mediated via a Ca2+-dependent, pertussis toxin-sensitive mechanism. These data suggest that galanin released by enteric nerves may act as a secretagogue in the human colon by activating Gal1-R.

Electrophysiological characterization of human distal colon epithelium isolated using a novel technique.

Electrophysiological studies of human colonic epithelia traditionally have been hampered by the lack of tissue availability and by poor tissue quality. Human colonic epithelium is usually obtained surgically from individuals with underlying disease, while surgery itself can injure or alter the resected tissue. As a result, a wide range in electrophysiological parameters is reported in previous studies of human colonic epithelium. Such factors may also account for differences in measurements between humans and the few other species studied. We therefore devised a novel and rapid endoscopic technique, endoscopic mucosal resection (EMR), that allows for the removal and study of intestinal mucosal epithelium from normal volunteers. Using EMR we rapidly (7.2+/-2.4 min) isolated surgical-sized epithelial sheets from the distal colon (1.4+/-0.4 by 1.3+/-0.4 cm) that were readily mounted in a 0.64-cm2 Ussing chamber. We observed stable resistance (289+/-30 omega cm2), potential difference (1.6+/-0.6 mV), and I(SC)(24+/-9 microA/cm2) for at least 90 min, after which all experiments were terminated. Exposure to carbachol increased I(SC)2.2+/-0.5-fold, while forskolin increased I(SC) 4.4+/-0.5-fold. These data show that the electrophysiological characteristics of the human distal colon removed by EMR more closely approximate values reported for other mammals than when removed using other techniques. Thus EMR represents a significant advance over traditional techniques for isolating human tissues and will increase the availability of this tissue for future studies.