title: Differing mechanisms of stimulation of Na+ absorption in rabbit proximal colon.
abstract: Both alpha2-adrenergic agonists and decreased Na+ in the bathing fluids stimulate electroneutral Na+ absorption in rabbit proximal colon, but it is unclear whether they have similar modes of action. We sought to define regulatory events involved with stimulation of Na+ absorption by these two agonists. Transport parameters were assessed by ion flux studies under short-circuit and pH stat conditions, recordings of intracellular electrical potential difference (psi(mc)) with microelectrode impalements, and measurement of intracellular pH (pH(i)). Epinephrine elicited a yohimbine-inhibitable alkalinization of pH(i) but did not alter psi(mc) In contrast, lowered serosal Na+ concentration ([Na+]) did not significantly increase pH(i) but did depolarize psi(mc). Removal of serosal HCO(3)- stimulated Na+ absorption and reversed residual ion flux from secretion to absorption. pH stat studies demonstrated epinephrine-stimulated, amiloride-inhibitable serosal alkalinization. Serosal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid inhibited Na+ absorption. Epinephrine and lowered [Na+] have different effects on intracellular parameters associated with electroneutral Na+ absorption. Epinephrine stimulates an apical Na+/H+ exchanger. Lowered [Na+] elicits responses consistent with a coupled Na+-HCO(3x)- exit step. Coordinated function of apical Na+/H+ exchangers and a basolateral Na+-HCO(3)(x)- symport permit Cl(-)-independent electroneutral Na+ absorption while maintaining pH(i) homeostasis. Given the low [Cl-] environment of the colonic lumen, this transport pathway may be important for electroneutral Na+ absorption.
authors.affiliation: Department of Internal Medicine, The University of Texas Medical School at Houston, 77030, USA.
authors.forename: J H
authors.initials: JH
authors.lastname: Sellin
authors.forename: R
authors.initials: R
authors.lastname: Desoignie
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D016764:Cell Polarity; D003106:Colon / Q000378:metabolism*; D004594:Electrophysiology; D004837:Epinephrine / Q000494:pharmacology / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D007408:Intestinal Absorption / Q000187:drug effects; D008297:Male; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism
chemical_list: D001639:Bicarbonates; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; C039614:ethylisopropylamiloride; D004837:Epinephrine