title: Secretin and somatostatin as modulators of electrolyte transport in guinea pig gallbladder epithelium.
abstract: Effects of secretin and somatostatin on electrolyte transport by guinea pig gallbladder epithelium were investigated in vitro. Tissues were mounted in Ussing-type chambers and continuously short-circuited to measure tissue conductance, short-circuit current (Isc) and transepithelial voltage. Unidirectional fluxes (from mucosa to serosa: Jms; from serosa to mucosa: Jsm) of Na+ and Cl- were determined simultaneously by using tracer techniques and those of HCO3- by pH-stat titration. Serosal addition of secretin caused concentration-dependent increases in tissue conductance, Isc and (lumen-negative) transepithelial voltage. At 1.3 x 10(-8) M, secretin raised net HCO3- secretion by 1.5 mumol/cm2/hr, due to inhibition of Jms (from approximately 1.2 to approximately 0.7 mumol/cm2/hr) and stimulation of Jsm (from approximately 3.7 to approximately 4.7 mumol/cm2/hr). The associated increase in Isc by approximately 3.8 mumol/cm2/hr (up from approximately 0.5 mumol/cm2/hr) was not different from net HCO3-secretion (approximately 4 mumol/cm2/hr). Neither Na+ nor Cl- net fluxes accounted for secretin-induced Isc, both being absorbed at equal rates (Na+: approximately 2.7, down from approximately 4.6 mumol/cm2/hr; Cl-: approximately 2.5, down from approximately 6.4 mumol/cm2/hr). Secretin caused a 10-fold rise of luminal efflux of cyclic AMP that was mitigated by somatostatin, added at 6 x 10(-7) M to the serosal bath. Somatostatin inhibited secretin- and prostaglandin E1-induced Isc, but was ineffective in tissues stimulated with 8-Br-cyclic AMP. It partly reverted the effects of secretin on JmsHCO3 and JsmHCO3, but had no effects in untreated tissues. Our data indicate that secretin converts HCO3-secretion from an electroneutral into an electrogenic process and blocks part of NaCl absorption.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Institut für Pharmakologie und Toxikologie, Medizinische Fakultät, Rheinisch-Westfälische Hochschule Aachen, Federal Republic of Germany.
authors.forename: G
authors.initials: G
authors.lastname: Sprakties
authors.forename: H J
authors.initials: HJ
authors.lastname: Macherey
authors.forename: K U
authors.initials: KU
authors.lastname: Petersen
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D000242:Cyclic AMP / Q000378:metabolism; D004573:Electrolytes / Q000378:metabolism*; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D005704:Gallbladder / Q000187:drug effects* / Q000378:metabolism; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D012633:Secretin / Q000494:pharmacology*; D013004:Somatostatin / Q000494:pharmacology*
chemical_list: D004573:Electrolytes; D012633:Secretin; D013004:Somatostatin; D000242:Cyclic AMP