vasoactive-intestinal-peptide and barium-chloride

In acute secretory diarrhoea the primary event driving fluid secretion is a transcellular, electrogenic, serosal to mucosal transport of chloride ions. Such transport requires the maintenance of an electrically negative cell membrane voltage, which is achieved through a basolateral outward leakage of potassium ions. The aim of this study was to investigate the nature of K(+) channel involvement in facilitating secretory processes in the human ileum. Muscle-stripped mucosal preparations of human ileal mucosa were set up in Ussing chambers for recording short-circuit current and transmucosal conductance. Escherichia coli heat-stable toxin and vasoactive intestinal peptide (VIP) produced concentration-dependent increases in short-circuit current. Responses to the heat-stable toxin were unaffected by basolateral application of 4-aminopyridine (5 mM), glibenclamide (10 microM) or a combination of charybdotoxin (0.3 microM) plus apamin (0.3 microM). However, basolateral barium (0.2-5 mM) caused a concentration-dependent inhibition. Responses to VIP were similarly affected by barium (0.05-1 mM). These results suggested that electrogenic chloride transport by human ileal mucosa required the presence of basolateral K(+) channels. The use of selective K(+)-channel inhibitors and low concentrations of barium suggested that the channels involved might be of the inwardly rectifying type.

Topics: 4-Aminopyridine; Apamin; Bacterial Toxins; Barium Compounds; Charybdotoxin; Chlorides; Glyburide; Humans; Ileum; Intestinal Mucosa; Potassium Channel Blockers; Potassium Channels; Vasoactive Intestinal Peptide

The factors which influence the exocytosis of mucins are not well characterized. Since the physical properties of mucins may be affected significantly by the co-secretion of electrolytes and water, we studied the relationship between ion movement and mucin secretion in T84 cells, a human colonic adenocarcinoma cell line which has been well characterized with respect to apical chloride secretion. Secretion of mucin was assessed by immunoassay of mucin appearing in the medium within 30 min of stimulation. Cells were grown on plastic in DMEM/Ham's F12 medium and experiments were carried out at 70% confluence. Mucin secretion was stimulated by the calcium ionophore A23187, or A23187 plus vasoactive intestinal polypeptide. Stimulated mucin secretion was not affected by loop diuretics (furosemide (1 x 10(-3) M) or bumetanide (1 x 10(-4) M)), with or without the addition of ouabain (5 x 10(-5) M) and amiloride (1 x 10(-5) M), making it unlikely that transcellular chloride movements in necessary for mucin secretion. However, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; (1 x 10(-5) and 5 x 10(-5) M) and three potassium channel blockers BaCl2 (1 x 10(-3) and 5 x 10(-3) M), tetraethylammonium chloride (1 x 10(-2) M) and quinine (5 x 10(-4) M) inhibited mucin secretion. A DIDS-sensitive chloride channel or chloride/bicarbonate exchanger and a Ca2(+)-dependent potassium channel may play important roles in mucin secretion. Since plasma membranes are sparingly permeable to DIDS, the DIDS-sensitive site is likely to be on the apical plasma membrane, perhaps at an initiation locus for exocytosis.

Topics: 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Adenocarcinoma; Amiloride; Barium; Barium Compounds; Calcimycin; Cell Line; Chlorides; Colonic Neoplasms; Furosemide; Humans; Kinetics; Mucins; Ouabain; Potassium Channels; Quinine; Stilbenes; Tetraethylammonium; Tetraethylammonium Compounds; Tumor Cells, Cultured; Vasoactive Intestinal Peptide

The divalent cation barium was used to study the role of calcium in coupling neuropeptide secretion and biosynthesis following secretagogue stimulation of bovine chromaffin cells. Barium chloride (0.1-2.5 mM) stimulated in a dose-dependent manner the secretion of met-enkephalin (up to 20% of intracellular peptide content) and increased the total amount (cell plus medium content) of met-enkephalin and vasoactive intestinal polypeptide (VIP) 2- to 3-fold after 72 hours. A greater than six-fold increase in proenkephalin mRNA (mRNA(enk)) was observed by 24 hours following barium stimulation. The voltage-sensitive calcium channel blocker D600 inhibited the barium-stimulated secretion of enkephalin and blocked the stimulation of VIP biosynthesis and mRNA(enk). Reducing calcium in the medium resulted in an enhancement of barium-stimulated release of both peptides, but blocked the induction of their biosynthesis. The data indicate that calcium targets involved in secretion can be activated by barium or calcium while calcium targets involved in biosynthesis specifically require calcium. It is therefore proposed that pathways leading to peptide secretion and biosynthesis in the adrenal diverge just after secretagogue-stimulated calcium influx.

Topics: Adrenal Medulla; Animals; Barium; Barium Compounds; Calcium Chloride; Cattle; Cells, Cultured; Chlorides; Chromaffin System; Enkephalin, Methionine; Gallopamil; In Vitro Techniques; Models, Biological; RNA, Messenger; Vasoactive Intestinal Peptide

The present study investigated whether there is a K+ conductive pathway on the basolateral membrane of pancreatic duct cells. Small inter- and intralobular ducts were isolated from rat pancreas and perfused in vitro. Duct cells were impaled and the potential across the basolateral membrane (PDbl) was measured. The resting potential was -61 +/- 1 mV. Ouabain (3 mmol/l) depolarized PDbl by 11 mV. Increase in the bath K+ concentration from 5 to 20 mmol/l depolarized PDbl by 15-16 mV. The effect of K+ channel blockers was tested. Ba2+ (1 mmol/l) added to the bath depolarized PDbl by 23-26 mV, whereas TEA+ (50 mmol/l) depolarized PDbl only by 7-8 mV. Dibutyryl cyclic AMP (0.5 mmol/l) depolarized PDbl by 20-30 mV. The results show that on the basolateral membrane of pancreatic duct cells there is a (Na+ + K+)-ATPase and a K+ conductive pathway sensitive to Ba2+.

Topics: Animals; Barium; Barium Compounds; Basement Membrane; Bicarbonates; Chlorides; Female; Ion Channels; Membrane Potentials; Ouabain; Pancreatic Ducts; Potassium; Rats; Rats, Inbred Strains; Secretin; Tetraethylammonium; Tetraethylammonium Compounds; Vasoactive Intestinal Peptide