title: Regulation of Na-Cl absorption in rabbit proximal colon in vitro.
abstract: Ion transport in rabbit proximal colon (PC) in vitro is dominated by a Na-Cl cotransport system stimulated by epinephrine. To further characterize the regulation of Na-Cl transport, we tested the effects of specific adrenergic agonists on ion fluxes under short-circuit conditions. Additionally, we tested the effects of the transport inhibitors bumetanide, furosemide, and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS). Basal Na and Cl absorption were essentially nil [Na net flux (JNanet) = 0.3 +/- 0.4, and Cl net flux (JClnet) = -0.5 +/- 0.5 mu eq X cm-2 X h-1, means +/- SE]. The alpha 2-agonist clonidine significantly increased net Na and Cl absorption (delta JNanet = 3.0 +/- 0.6 mu eq X cm-2 X h-1, delta JClnet = 2.0 +/- 0.4 mu eq X cm-2 X h-1) with a minimal change in short-circuit current (delta Isc = 0.1 +/- 0.1 mu eq X cm-2 X h-1). The alpha 1-agonist phenylephrine and the beta-agonist isoproterenol did not alter ion transport. The alpha 2-blocker yohimbine (YOH) had a complex, concentration-dependent effect. At low concentrations (10(-6)-10(-8) M) YOH effectively inhibited epinephrine-stimulated cotransport. Compared with 10(-8)M YOH, 10(-6) YOH blocked 90% of the epinephrine-induced increases in Na and Cl absorption.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000818:Animals; D002034:Bumetanide / Q000494:pharmacology; D003106:Colon / Q000502:physiology*; D004837:Epinephrine / Q000494:pharmacology; D005665:Furosemide / Q000494:pharmacology; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects; D007700:Kinetics; D008297:Male; D011224:Prazosin / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011817:Rabbits; D012965:Sodium Chloride / Q000378:metabolism*; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D002034:Bumetanide; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D015016:Yohimbine; D012965:Sodium Chloride; D005665:Furosemide; D011433:Propranolol; D011224:Prazosin; D004837:Epinephrine