ISSN:
1432-1912
Keywords:
Transport regulation
;
VIP
;
VIP antagonist
;
Histamine
;
Noradrenaline
;
Somatostatin
;
Cl− channel blocker
;
TMB 8
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary In guinea-pig gallbladder epithelium, cAMP converts electroneutral HCO inf3 sup− secretion into an electrogenic process. The effects of blood side Ba2+ (5 mmol/l) on HCO inf3 sup− tranport were investigated in vitro, using pH-stat and voltage clamp techniques to determine unidirectional fluxes of HCO inf3 sup− and transepithelial electrical characteristics. Serosal, not mucosal addition of Ba2+ elevated short-circuit current (Isc), transepithelial potential difference, and tissue conductance; it inhibited the absorptive HCO inf3 sup− flux while leaving the secretory flux unchanged. The Isc effect of Ba2+ was inhibited or prevented by tetrodotoxin; D- and Lrpropranolol; the Cl− channel blocker 4-N-methyl-N-phenylaminothiophene-3-carboxylic acid; the intracellular Ca2+ antagonist, 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester; noradrenaline, by a yohimbine-sensitive action; somatostatin; HCO inf3 sup− -free solutions. Thus Ba2+ appeared to release a neurotransmitter that gives rise to CAMP synthesis sufficcient to turn part of electroneutral HCO inf3 sup− secretion electrogenic. In a search for the involved signalling pathways, the H1-receptor antagonist, cetirizine, largely and hexamethonium, atropine, atenolol, indomethacin, and trifluoperazine entirely failed to antagonize the Isc effect of Ba2+. Similarly, carbachol, dobutamine, salbutamol, and serotonin were unable to mimick the action of Ba2+ and Isc effects of histamine were small and short-lived. By contrast, vasoactive intestinal peptide (VIP; 3 × 10−7 mol/l) completely transformed HCO inf3 sup− secretion into an electrogenic process. The VIP receptor antagonist (4Cl-dPhe6, Leu17)VIP, delayed and reduced the Isc responses to Ba2+ and VIP. As guinea-pig gallbladder epithelial cells possess cAMP-coupled VIP receptors close to VIPergic neurons, Ba2+ is likely to act by releasing VIP from neural terminals.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00173214
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