Compartmentalization of extracellular cGMP determines absorptive or secretory responses in the rat jejunum

Abstract

Angiotensin II (ANG II) regulates sodium and water transport across epithelial cells in the kidney and gastrointestinal tract (1-5). In the jejunum, low concentrations of ANG II stimulate sodium and water absorption while high concentrations inhibit absorption and/or stimulate secretion (3). We have recently demonstrated that ANG II stimulates absorption in the jejunum by an action at the AT 2 receptor involving the generation of guanosine cyclic 3′,5′-monophosphate (cGMP) (3,6,7).In this study, we hypothesized that ANG II increases jejunal sodium and water absorption by increasing the synthesis of nitric oxide (NO) and stimulating soluble guanylyl cyclase. However, since cGMP is thought to mediate secretory, not absorptive, responses in the gastrointestinal tract when particulate guanylyl cyclase (GC-C) is stimulated by the heat-stable enterotoxin of Escherichia coli (STa) or guanylin or uroguanylin (8, 9), we hypothesized that the sodium and water transport response, absorptive or secretory, is associated with a compartmentalized cGMP response via either soluble or particulate guanylyl cyclase. If so, STa would stimulate secretion by stimulating particulate guanylyl cyclase on the apical cell membrane of transporting epithelial cells. In contradistinction, nitric oxide would stimulate absorption via soluble guanylyl cyclase from the serosal side, and cGMP would be released predominantly across the basolateral membrane of epithelial cells into the interstitial space. We introduced both in situ loop and microdialysis techniques to test these hypotheses. MethodsAnimal preparation. Male Wistar rats weighing 200 ± 15 g were obtained from Harlan Bioproducts Inc. (Indianapolis, Indiana, USA). Rats were housed in a room with 12-h light-dark cycles and maintained on standard rat chow containing 0.28% NaCl or low-sodium chow containing 0.08% NaCl (BioServe Biotechnologies, Frenchtown, New Jersey, USA). Rats were fasted overnight before the study.Operative procedure. Rats (n = 8 in each group) were anesthetized with pentobarbital sodium 70 mg/kg intraperitoneally (Veterinary Laboratories, Inc., Lenexa, Kansas). The trachea and left jugular vein were cannulated. A venous cannula (PE 50) was connected to a Harvard 975 infusion pump (Harvard Apparatus Co., South Natick, Massachusetts, USA) through which lactated Ringer's solution (vehicle) and drugs were infused. A ventral midline celiotomy also was performed and the jejunum was prepared in two different ways as described below.Single-pass perfusion. These studies were performed according to previous publications (10, 11). An inlet cannula was placed just below the duodenal-jejunal flexure and the outlet cannula was 15 cm distal to the inlet cannula. The lumen just proximal and distal to the cannulated segment was tied off. To measure water transport, lactated Ringer's solution containing [ 14 C]inulin (15,000 dpm/ml; 2.2 µCi/mg specific activity; New England Nuclear, Boston, Massachusetts, USA) and phenol red (50 mg/liter, Sigma Chemical Company; St. Louis, Missouri, We ex...

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Renal Interstitial cGMP Mediates Natriuresis by Direct Tubule Mechanism

“…The infusion rate of cGMP was selected as a pharmacological dose that was 4-fold greater than that used in our previous studies in the rat jejunum. 26 In separate experiments, the NOS inhibitor N G -nitro-L-arginine methyl ester (L-NAME, 100 ng · kg…”

cGMP Inhibition of Na+/H+ Antiporter 3 (NHE3) Requires PDZ Domain Adapter NHERF2, a Broad Specificity Protein Kinase G-anchoring Protein

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