pituitrin and fenamic-acid

A number of transporters and channels have been identified in cholangiocytes, but the role that bile ducts play in the formation of bile in vivo is unclear. We determined the contribution of cholangiocytes to bile flow and biliary bicarbonate excretion in normal rat liver.. Bile flow and biliary bicarbonate were measured in isolated rat livers perfused via both the portal vein and the hepatic artery because the hepatic artery provides the blood supply to bile ducts. Livers were perfused with secretin or acetylcholine (ACh), which respectively increase either adenosine 3',5'-cyclic monophosphate (cAMP) or cytosolic Ca(2+) in cholangiocytes. Livers also were perfused with glucagon or vasopressin to instead increase cAMP or cytosolic Ca(2+) in hepatocytes.. Secretin increased biliary bicarbonate in a dose-dependent fashion and was much more effective when administered via the hepatic artery. Secretin did not affect bile flow. Similarly, ACh increased bicarbonate excretion when infused via the hepatic artery but not the portal vein. The effects of secretin were augmented by ACh, and this was prevented by cyclosporin A. The effects of ACh were blocked by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), 5-nitro2-(3-phenylpropylamino)benzoic acid (NPPB), or diphenylamine-2-carboxylic acid (DPC), and the effects of secretin were inhibited by NPPB or DPC and unaffected by DIDS. Neither glucagon nor vasopressin altered biliary bicarbonate.. Biliary bicarbonate is regulated by cholangiocytes rather than hepatocytes in normal rat liver. ACh-induced bicarbonate excretion depends on both chloride channels and bicarbonate exchange, whereas secretin-induced bicarbonate excretion is independent of bicarbonate exchange.

Topics: 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Acetylcholine; Angiogenesis Inhibitors; Animals; Anti-Inflammatory Agents, Non-Steroidal; Bicarbonates; Bile; Bile Ducts; Biological Transport; Calcium; Cyclic AMP; Cyclosporine; Dose-Response Relationship, Drug; Enzyme Inhibitors; Epithelial Cells; Glucagon; Hepatic Artery; Hepatic Veins; In Vitro Techniques; Liver; Male; Nitrobenzoates; ortho-Aminobenzoates; Rats; Rats, Sprague-Dawley; Secretin; Vasoconstrictor Agents; Vasodilator Agents; Vasopressins

We hypothesized that inhibition and activation of basolateral to luminal chloride transport mechanisms were associated with respective decreases and increases in basolateral to luminal water fluxes. The luminal to basolateral (J(W)(L-->B)) and basolateral to luminal (J(W)(B-->L)) water fluxes across ovine tracheal epithelia were measured simultaneously. The mean J(W)(L-->B) (6.5 microl/min/cm(2)) was larger than J(W)(B-->L) (6.1 microl/min/cm(2)). Furosemide reduced J(W)(B-->L) from 6.0 to 5.6 microl/min/cm(2). Diphenylamine-2-carboxylate (DPC) reduced J(W)(B-->L) from 7.9 to 7. 3 microl/min/cm(2) and reduced the membrane potential difference by 38%. Furosemide together with DPC decreased J(W)(L-->B) by 30% and J(W)(B-->L) by 15%. Norepinephrine increased J(W)(B-->L) from 4.9 to 6.0 microl/min/cm(2). Neuropeptide Y in the presence of norepinephrine decreased J(W)(L-->B) (6.4 to 5.2 microl/min/cm(2)) and returned J(W)(B-->L) to its baseline value. Vasopressin increased J(W)(B-->L) from 4.1 to 5.1 microl/min/cm(2). Endothelin-1 induced a simultaneous increase in J(W)(B-->L) (7.0 to 7.7 microl/min/cm(2)) and decrease in J(W)(L-->B) (7.4 to 6.4 microl/min/cm(2)); and decreased the membrane resistance. These data indicate that in tracheal epithelia under homeostatic conditions J(W)(B-->L) has a approximately 15% actively coupled component. Consistent with our hypothesis, inhibition and receptor-induced stimulation of chloride effluxes were associated with decreases and increases in J(W)(B-->L), respectively. However, as inhibition of transcellular chloride transport always decreased J(W)(L-->B) more than J(W)(B-->L), reducing transepithelial chloride transport did not result in less water being transported into the airway lumen.

Topics: Adrenergic alpha-Agonists; Animals; Biological Transport; Calcium Channel Blockers; Chlorides; Endothelin-1; Furosemide; In Vitro Techniques; Neuropeptide Y; Norepinephrine; ortho-Aminobenzoates; Respiratory Mucosa; Sheep; Trachea; Vasopressins; Water

1. The effect of sulphonylurea drugs on hydrosmotic flow across toad urinary bladder epithelium was re-evaluated in the present study. Glibenclamide, added to the basolateral medium, significantly enhanced the osmotic flow induced by low doses of antidiuretic hormone (ADH) or forskolin (FK), while it inhibited the effect of exogenous cyclic adenosine monophosphate (cAMP) or its non-hydrolysable bromo derivative, 8-Br-cAMP, added to the basolateral medium. These opposite effects of glibenclamide on the transepithelial osmotic flow can be explained by a reduction of cAMP permeability across the basolateral membrane of the epithelium. The decrease in cAMP permeability leads, according to the direction of the cAMP gradient, to firstly an enhanced osmotic flow when cAMP is generated intracellularly by addition of ADH and FK, glibenclamide reducing cAMP exit from the cell, and secondly a decreased osmotic flow in response to cAMP (and 8-Br-cAMP) added to the basolateral medium, glibenclamide inhibiting, in this case, their entry into the cell. 2. The demonstration that glibenclamide actually inhibits the basolateral cAMP permeability rests on the fact that firstly it decreases the release of cAMP into the basolateral medium by about 40 %, at each concentration of ADH or forskolin tested, secondly it increases the cAMP content of paired hemibladders incubated in the presence of ADH or FK, when intracellular degradation was prevented by phosphodiesterase inhibition, and thirdly it decreases also the uptake of basolateral 8-Br-[3H]cAMP into paired toad hemibladders. 3. Taken together, the present data demonstrate that glibenclamide inhibits the toad urinary bladder basolateral membrane permeability to cAMP, most probably by a direct interaction with a membrane protein not yet indentified but distinct from the sulphonylurea receptor.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Animals; ATP-Binding Cassette Transporters; Bufo marinus; Calcium Channel Blockers; Colforsin; Cyclic AMP; Dose-Response Relationship, Drug; Epithelium; Glyburide; In Vitro Techniques; Membrane Fluidity; ortho-Aminobenzoates; Osmosis; Permeability; Pinacidil; Potassium Channels; Potassium Channels, Inwardly Rectifying; Receptors, Drug; Sulfonylurea Receptors; Urinary Bladder; Vasodilator Agents; Vasopressins; Water

Cl- channels in the medullary thick ascending limb (MTAL) studied by either patch-clamp technique or reconstitution into lipid bilayers are activated by increases in intracellular Cl- concentrations. rbClC-Ka, a ClC Cl- channel, may represent this channel. We therefore evaluated the role of rbClC-Ka in transcellular MTAL Cl- transport in two separate ways. First, an antibody was raised against a fusion protein containing a 153-amino acid fragment of rbClC-Ka. Immunostaining of rabbit kidney sections with the antibody was localized to basolateral regions of MTAL and cortical thick ascending limb (CTAL) segments and also to the cytoplasm of intercalated cells in the cortical collecting duct. Second, Cl- uptake and efflux were measured in suspensions of mouse MTAL segments. Cl- uptake was bumetanide sensitive and was stimulated by treatment with a combination of vasopressin + forskolin + dibutyryl adenosine 3',5-cyclic monophosphate (DBcAMP). Cl- efflux was also increased significantly by vasopressin + forskolin + DBcAMP from 114 +/- 20 to 196 +/- 36 nmol.mg protein-1.45 s-1 (P = 0.003). Cl- efflux was inhibited by the Cl- channel blocker diphenylamine-2-carboxylate (154 +/- 26 vs. 70 +/- 21 nmol.mg protein-1.45 s-1, P = 0.003). An anti-rbClC-Ka antibody, which inhibits the activity of MTAL Cl- channels in lipid bilayers, reduced Cl- efflux from intact MTAL segments (154 +/- 28 vs. 53 +/- 14 nmol.mg protein-1.45 s-1, P = 0.02). These results support the view that rbClC-Ka is the basolateral membrane Cl- channel that mediates vasopressin-stimulated net Cl- transport in the MTAL segment.

Topics: Animals; Antibodies; Bucladesine; Calcium Channel Blockers; Cell Membrane; Chloride Channels; Chlorides; Colforsin; Guinea Pigs; In Vitro Techniques; Kidney Medulla; Kidney Tubules; Mice; ortho-Aminobenzoates; Rabbits; Vasopressins

We have investigated the cellular signalling pathway by which vasopressin stimulates a Ca2(+)-dependent Cl- conductance and the effects of two known Cl- channel blockers in cultured rat A7r5 aortic smooth muscle cells using anion efflux and fluorescent Ca2+ imaging studies. Addition of vasopressin (100 nM) to A7r5 cells enhanced 125I (Cl- substitute) efflux from the cells through a V1 receptor-mediated pathway. Maximal increases in the rate of efflux were observed 1 min following addition of vasopressin (4-fold above basal levels). Activation of the V1 pathway was demonstrated by an increase in inositol trisphosphate (IP3) formation and lack of cAMP accumulation by the cells following the addition of vasopressin. Fluorescent ratio imaging with fura-2 revealed that addition of vasopressin to the cells results in an increase of [Ca2+]i which peaks within 20 s and does not return to resting levels during the 100 s observation period. The addition of a Ca2+ ionophore mimicked the vasopressin-induced efflux from the cells. 5-Nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) and a chloro-substituted compound (cpd 149) inhibited the vasopressin-stimulated 125I efflux from the cells. The concentrations of NPPB and cpd 149 required to inhibit 125I efflux from the cells were similar to those which also attenuated vasopressin-induced Ca2+ transients in the cells. NPPB and cpd 149 had no effects on the ionomycin stimulated efflux. The mechanism(s) by which cpd 149 exerts its effect on stimulated efflux was examined by measuring its action on vasopressin-induced changes in IP3. Compound 149 inhibited IP3 generation in response to vasopressin.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Aorta, Thoracic; Calcium; Cell Line; Chloride Channels; Colforsin; Cyclic AMP; Homeostasis; Inositol Phosphates; Iodine; Iodine Radioisotopes; Membrane Proteins; Muscle, Smooth, Vascular; Nitrobenzoates; ortho-Aminobenzoates; Rats; Vasopressins