Biomedical subjects

A L Finn

Publications and source records attributed to A L Finn.

At least 19 recordsLinked to original sources

PubMed1992

Reconstitution and regulation of an epithelial chloride channel.

We have used a monoclonal antibody (MAb E12), one of several such antibodies raised against theophylline-treated Necturus gallbladder epithelial cells, to isolate a chloride channel protein by the use of an immunoaffinity column and FPLC. This protein (M(r) 219,000) has been reconstituted into a planar lipid bilayer, where it behaves as a chloride-selective channel (PCl/PNa = 20.2; PNa/PK = 1) whose unit conductance is 62.4 +/- 4.6 pS. Antibody added to the trans side (there is no effect from the cis side) causes channel open probability to drop to virtually zero, but has no effect on the conductance or the selectivity of single channels. To test the role of phosphorylation in the activity of the native channel, we studied the effects of the protein phosphatase inhibitor okadaic acid (OA) on intact gallbladders, and showed that channels opened by theophylline treatment and closed by antibody are reopened reversibly by OA (0.01-1.0 microM). Addition of the catalytic subunit of protein phosphatase 2A (PP-2A) to the cis side of a bilayer containing reconstituted chloride channels caused closure of the channels after a delay, and subsequent addition of ATP and the catalytic subunit of cAMP-dependent protein kinase (PKA) caused immediate reopening. These data indicate that (a) this chloride channel protein inserts in a directed way into the bilayer such that the cis side is 'intracellular', (b) the purified channel protein is phosphorylated, and (c) gating from the cellular side is controlled by the direct phosphorylation and dephosphorylation of the channel protein.

Animals↗

PubMed1992

Regulation of an epithelial chloride channel by direct phosphorylation and dephosphorylation.

A native chloride channel in Necturus gallbladder epithelial cells is opened by a theophylline-induced rise in cellular cyclic AMP and is closed by removal of theophylline or by addition of specific antibody; however, it does not close if okadaic acid, an inhibitor of protein phosphatases 1 and 2A, is added. The purified channel reconstituted into lipid bilayers closes upon the addition of protein phosphatase 2A and is reopened by the addition of Mg-ATP and the catalytic subunit of cyclic AMP-dependent protein kinase. These results indicate that the channel protein is purified in a phosphorylated state and that its functional characteristics are at least partly controlled by direct phosphorylation and dephosphorylation.

Animals↗

PubMed1992

Toxicity and side effects of ondansetron.

The safety of ondansetron has been carefully evaluated through laboratory studies and clinical trials. Preclinical studies demonstrated that there is no end-organ toxicity in rats and dogs administered ondansetron doses 30 to 100 times those used in humans. At near-lethal doses of ondansetron, animals developed subdued activity, ataxia, and convulsions. Modest transient increases in serum transaminase values were observed. Concurrent administration of ondansetron with chemotherapy had no effect on tumor response in animals. The clinical safety of ondansetron has been evaluated in more than 2,500 cancer patients who received intravenous doses as large as 1.5 mg/kg. In adult patients receiving single-day chemotherapy, the incidence of adverse events was 36% with ondansetron (n = 647) and 50% with metoclopramide (n = 498). Diarrhea occurred in 9% of ondansetron patients and 19% of metoclopramide patients. Headache occurred in 14% of ondansetron patients and 8% of metoclopramide patients. Extra-pyramidal symptoms were reported in none of the ondansetron patients and 5% of the metoclopramide patients. The incidence of vascular occlusive events and seizure disorders was nearly identical with ondansetron and metoclopramide and similar to the cancer population in general. In a group of 209 pediatric patients receiving chemotherapy, the incidence of adverse events was 19% with ondansetron. Serum transaminase values increased significantly in 6% to 8% of ondansetron patients and 2% of metoclopramide patients. There was no apparent relationship between the cumulative dose of ondansetron administered and the incidence of increased transaminase values. However, there was an apparent relationship between the cumulative dose of cisplatin administered and the incidence of transaminase abnormalities. These data demonstrate that ondansetron is better tolerated than metoclopramide and is safe for intravenous administration to pediatric and adult patients receiving chemotherapy.

Animals↗

PubMed1992

The delayed-emesis syndrome from cisplatin: phase III evaluation of ondansetron versus placebo.

Cisplatin may evoke both an acute emetic response during the first 24 hours following treatment and a less well-recognized syndrome of delayed emesis. While delayed emesis is usually less severe in terms of frequency of vomiting episodes, the problem continues to result in significant morbidity. In comparison with acute emesis, the exact pathogenesis of the delayed emesis syndrome remains unclear. Although a combination of oral metoclopramide and dexamethasone is effective in many patients in preventing delayed emesis, almost 50% continue to experience at least one emetic episode when treated with this regimen. A phase III multicenter study has evaluated oral ondansetron versus placebo in the prevention of the delayed-emesis syndrome in 50 patients during days 2 through 5 following high-dose cisplatin administration. Although the daily rates of complete emetic control, failure, and control of nausea favor ondansetron, this trial is statistically inconclusive in establishing efficacy of ondansetron as a single agent in the prevention of delayed emesis. Ondansetron was well tolerated in the dose and schedule used.

Adult↗

PubMed1991

Reconstitution of an epithelial chloride channel. Conservation of the channel from mudpuppy to man.

We have previously shown that monoclonal antibody E12 (MAb E12), one of several such antibodies raised against theophylline-treated Necturus gallbladder (NGB) epithelial cells, inhibits the chloride conductance in the apical membrane of that tissue. Since chloride channels are critical to the secretory function of epithelia in many different animals, we have used this antibody to determine whether the channels are conserved, and in an immunoaffinity column to isolate the channel protein. We now demonstrate that MAb E12 cross-reacts with detergent-solubilized extracts of different tissues from various species by enzyme-linked immunosorbent assay (ELISA). Western blot analysis shows that this monoclonal antibody recognizes proteins of Mr 219,000 in NGB, toad gallbladder, urinary bladder, and small intestine, A6 cells, rat colon, rabbit gastric mucosa, human lymphocytes, and human nasal epithelial cells, and inhibits the chloride conductance in toad gallbladder, rat colon, and human nasal epithelium. Detergent-solubilized protein eluted from an immunoaffinity column and then further purified via FPLC yields a fraction (Mr 200,000-220,000) which has been reconstituted into a planar lipid bilayer. There it behaves as a chloride-selective channel (PCl/PNa = 20.2 in a 150/50 mM trans-bilayer NaCl gradient) whose unit conductance is 62.4 +/- 4.6 pS, and which is blocked in the bilayer by the antibody. The gating characteristics of this channel indicate that it can exist as aggregates or as independent single channels, and that the antibody interferes with gating of the aggregates, leaving the unit channels unchanged. From these data we conclude that the protein of Mr 219,000 recognized by this monoclonal antibody is an important component of an epithelial chloride channel, and that this channel is conserved across a wide range of animal species.

Animals↗

PubMed1991

Effects of ranitidine, given t.d.s., on intragastric and oesophageal pH in patients with gastrooesophageal reflux.

The purpose of this study was to determine the effects of 150 mg ranitidine, 300 mg ranitidine or placebo, administered every 8 h, on gastro-oesophageal pH and heartburn parameters in reflux patients. Twelve symptomatic reflux patients received each of the three treatments in a randomized, double-blind, crossover fashion. Intragastric and oesophageal pH were monitored continuously for a 24 h period. Meals were standardized, consumed at set times and patients were allowed to recline and sleep from 23.00 hours until 06.00 hours only. The gastric record was analysed for the percentage of time that the pH was greater than or equal to 4. The oesophageal record was analysed for acid contact time (percentage time (%) pH less than or equal to 4.0) and reflux episode frequency. Finally, patients recorded each new episode of heartburn and graded daytime heartburn severity at the end of each hour. Ranitidine increased the median (%) time that the intragastric pH remained at or above 4, from 4.5 (placebo) to 33.9% (150 mg dose) and 33.3% (300 mg dose). Ranitidine dose-dependently reduced the median 24-hour oesophageal acid contact time from 13.3% (placebo) to 6.8% (150 mg dose) and 2.5% (300 mg dose). The 300 mg dose significantly reduced daytime heartburn episode frequency and severity while the 150 mg dose reduced heartburn severity only. We conclude that 150 and 300 mg doses of ranitidine administered every 8 h have major, sometimes dose-dependent effects on the objective parameters and symptoms of gastro-oesophageal reflux.

Adult↗

PubMed1991

Ondansetron (GR 38032F): a novel antiemetic effective in patients receiving a multiple-day regimen of cisplatin chemotherapy.

In a multicenter trial, we evaluated the antiemetic efficacy of ondansetron, a selective serotonin type 3 (5-HT3) receptor antagonist, in 42 adult chemotherapy-naïve patients receiving a multiple-day cisplatin regimen (20-40 mg/m2 per day for 4-5 days). Thirty-one patients received 3 daily doses of ondansetron (0.15 mg/kg) given intravenously every 6 hours (first dose 30 minutes prior to cisplatin administration); 11 additional patients received an identical dosage and schedule except that a fourth daily dose was added 17.5 hours after cisplatin administration. No other antiemetics were administered. Forty patients were evaluable for efficacy response. Thirteen patients (33%) had no vomiting at any time during the 5-day study. When emetic episodes were evaluated on a daily basis, complete protection (zero emetic episodes) ranged from 50-75%, and major protection (less than or equal to 2 emetic episodes) ranged from 65-93%. The majority of therapy failures occurred on days 3 and 4. Side effects were minor and transient; no extrapyramidal side effects were observed. Ondansetron appears to be a safe and effective antiemetic when administered during a multiple-day cisplatin-containing chemotherapy regimen.

Adolescent↗

PubMed1990

Efficacy of ondansetron (GR 38032F) and the role of serotonin in cisplatin-induced nausea and vomiting.

We compared the efficacy and safety of ondansetron (GR 38032F), a selective antagonist of serotonin S3 receptors, with that of placebo in controlling the nausea and vomiting induced by cisplatin treatment in 28 patients with cancer. The patients received either three intravenous doses of ondansetron (0.15 mg per kilogram of body weight) or normal saline (placebo) at four-hour intervals, beginning 30 minutes before the administration of cisplatin. Nausea and vomiting were markedly diminished in the group given ondansetron. The median time to the first episode of emesis was 2.8 hours in the placebo group and 11.6 hours in the ondansetron group (P less than 0.001); the median number of episodes in 24 hours was 5.5 in the placebo group and 1.5 in the ondansetron group (P less than 0.001); the mean (+/- SEM) number of regurgitations or dry heaves per episode was 3.2 +/- 0.5 in the placebo group and 1.17 +/- 0.1 in the ondansetron group (P less than 0.001). None of the 14 patients given ondansetron, but 12 of 14 given placebo, required treatment with antiemetic-rescue agents for the control of nausea and vomiting. There were no adverse effects attributable to ondansetron. The urinary excretion of 5-hydroxyindoleacetic acid, the main metabolite of serotonin, was increased in all patients two to six hours after they received cisplatin chemotherapy, and the increases paralleled the episodes of emesis. We conclude that ondansetron is an effective and safe agent for controlling the nausea and vomiting induced by cisplatin treatment. We suggest that cisplatin treatment increases the release of serotonin from enterochromaffin cells, and that ondansetron acts by blocking S3 receptors for serotonin.

Adult↗

PubMed1990

Antagonism of serotonin S3 receptors with ondansetron prevents nausea and emesis induced by cyclophosphamide-containing chemotherapy regimens.

The control of nausea and emesis in cancer patients receiving chemotherapy poses a significant management problem. In this randomized, double-blind, placebo-controlled study, we evaluated the effect of serotonin S3 receptor blockade with ondansetron (GR 38032F) on the prevention of nausea and vomiting induced by cyclophosphamide-containing chemotherapy. Cyclophosphamide was given in doses of 500 to 600 mg/m2 and ondansetron as three intravenous (IV) doses of 0.15 mg/kg. Most patients had breast cancer. Cyclophosphamide was given in combination with doxorubicin (65% of patients) or with fluorouracil (85% of patients: 50% with Adriamycin [doxorubicin; Adria Laboratories, Columbus, OH] and 35% with methotrexate). All placebo-treated patients experienced vomiting, whereas 70% of patients treated with ondansetron did not vomit (P = .008). Median nausea scores were 8 mm on ondansetron and 65 mm on placebo (P less than .001). Seventy percent of patients treated with ondansetron retained their normal appetite, compared with 10% of placebo patients. Adverse events occurred in six placebo patients and one ondansetron patient. Diarrhea and headache were the most common events, both occurring more frequently in the placebo group. There were no extrapyramidal reactions, and the only significant biochemical change occurred in a placebo-treated patient. These results suggest that serotonin S3 receptor antagonists represent a novel, effective, and safe mode of therapy for nausea and emesis induced by cyclophosphamide-containing chemotherapies. In addition, our observations are compatible with the view that serotonin, acting on S3 receptors, mediates the nausea and emesis occurring after cyclophosphamide chemotherapy.

Adult↗

PubMed1990

Ondansetron: a new antiemetic for patients receiving cisplatin chemotherapy.

GR 38032F (ondansetron) is a selective serotonin subtype-3 receptor antagonist with reported antiemetic efficacy in patients receiving cisplatin. This study evaluated the safety and efficacy of ondansetron in three consecutive nonrandomized groups of patients who were receiving a 4- or 5-day regimen of cisplatin (20 to 40 mg/m2/d) combination chemotherapy. Thirty-six patients were enrolled. Thirty-five patients were assessable for efficacy. All patients received three daily intravenous doses of 0.15 mg/kg of ondansetron. Twenty-four patients had received no prior chemotherapy. Twelve of these received ondansetron every 2 hours and 12 received ondansetron every 6 hours. Twelve additional patients who had received at least one prior course of chemotherapy were administered ondansetron every 6 hours. All patients were monitored for emetic episodes (vomiting or retching), adverse events, and laboratory safety parameters. Ten patients (29%) had no vomiting or retching throughout the entire study period and 18 patients (51%) experienced two or fewer emetic episodes during the entire study period. The greatest antiemetic efficacy was on day 1 when 27 patients (77%) had no emesis. The chemotherapy-naive patients responded better than the nonnaive patients on all study days. Reported adverse events were minor, with the most common possibly drug-related event being headache (14% of patients). No extrapyramidal symptoms were observed. Transient increases in total SGOT, and SGPT were observed in some patients.

Adult↗

PubMed1989

Monoclonal antibodies to the apical chloride channel in Necturus gallbladder inhibit the chloride conductance.

Monoclonal antibodies raised by injecting Necturus gallbladder cells into mice were tested for their ability to inhibit the apical chloride conductance induced by elevation of cellular cAMP. Five of these monoclonal antibodies bound to the apical cells, as shown by indirect immunofluorescence microscopy, and inhibited the chloride conductance; one antibody that bound only to subepithelial smooth muscle, by indirect immunofluorescence microscopy, showed no inhibition of chloride transport. The channel or a closely related molecule is present in the membrane whether or not the pathway is open, since, in addition to inhibiting the conductance of the open channel, the antibody also bound to the membrane in the resting state and prevented subsequent opening of the channel. The antibody was shown to recognize, by ELISA, epitopes from the Necturus gallbladder and small intestine. Finally, by Western blot analysis of Necturus gallbladder homogenates, the antibody was shown to recognize two protein bands of Mr 219,000 and Mr 69,000. This antibody should permit isolation and characterization of this important ion channel.

Animals↗

PubMed1988

The timing of evening meal and ranitidine administration--effects on patterns of 24 hour intragastric acidity.

Intragastric pH-metry was utilized to assess the effect of the time of meal ingestion and ranitidine administration on 24-h intragastric acidity. Twelve volunteers with a documented history of duodenal ulcer were studied in a four-way crossover design. Subjects randomly received ranitidine at 18.00 and 22.00 hours, with and without food. Serial blood samples were collected and analysed for ranitidine by high pressure liquid chromatography. Over the interval of 18.00-0.700 hours, the mean hydrogen-ion activity was significantly lower with the 18.00 hour dose than with the 22.00 hour dose (P less than or equal to 0.05). There were no differences between the four treatments in median pH or mean hydrogen-ion activity over the 23-h study interval. There were no differences between treatments in peak ranitidine concentrations, time to peak concentration, area under the serum-concentration time curve or elimination half-life.

Adult↗

PubMed1988

Potassium-induced cell swelling in Necturus gallbladder epithelium.

In Necturus gallbladder epithelium, elevation of mucosal K+ to 95 mM in the presence of 10 mM Na+ resulted in cell swelling at a rate of 3.2% original volume per minute, followed by volume-regulatory shrinking. When Na+ was completely removed from or when amiloride (10(-4) M) was added to the mucosal medium, K+-induced cell swelling was abolished. In the presence of 10 mM Na+, 1 mM Ba2+ abolished and substitution of mucosal Cl- by NO-3 had no effect on K+-induced swelling. Thus solute entry following elevation of mucosal K+ is effected by separate K+ and Cl- pathways. Furthermore, substitution of 95 mM K+ for Na+ in the mucosal bathing medium leads to the development of a Cl- conductance in the basolateral membrane as long as some Na+ remains in the medium. However, cell swelling induced by mucosal dilution does not lead to the appearance of a Cl- conductance. Thus the activation of this conductance requires both swelling and membrane depolarization. These results show that 1) high mucosal K+ leads to cell swelling due to the entry of Cl- along with K+ and the Cl- can enter across either membrane, 2) the Cl- pathways require the presence of mucosal Na+, and 3) cell volume regulation is activated by an increase in volume per se, i.e., a hyposmotic exposure is not required for volume regulation to occur.

Animals↗

PubMed1987

Characterization of the basolateral membrane conductance of Necturus urinary bladder.

Necturus urinary bladders stripped of serosal muscle and connective tissue were impaled through their basolateral membranes with microelectrodes in experiments that permitted rapid changes in the ion composition of the serosal solution. The transepithelial electrical properties exhibited a marked seasonal variation that could be attributed to variations in the conductance of the shunt pathway, apical membrane selectivity, and basolateral Na+ transport. In contrast, the passive electrical properties of the basolateral membrane remained constant throughout the year. The apparent transference numbers (Ti) of the basolateral membrane for K+ and Cl- were determined from the effect on the basolateral membrane equivalent electromotive force of a sudden increase in the serosal K+ concentration from 2.5 to 50 mM/liter or a decrease in the Cl- concentration from 101 to 10 mM/liter. TK and TCl were 0.71 +/- 0.05 and 0.04 +/- 0.01, respectively. The basolateral K+ conductance could be blocked by Ba2+ (0.5 mM), Cs+ (10 mM), or Rb+ (10 mM), but was unaffected by 3,4-diaminopyridine (100 microM), decamethonium (100 microM), or tetraethylammonium (10 mM). We conclude that a highly selective K+ conductance dominates the electrical properties of the basolateral membrane and that this conductance is different from those found in nerve and muscle membranes.

4-Aminopyridine↗

PubMed1987

Interaction between the basolateral K+ and apical Na+ conductances in Necturus urinary bladder.

Experimental modulation of the apical membrane Na+ conductance or basolateral membrane Na+-K+ pump activity has been shown to result in parallel changes in the basolateral K+ conductance in a number of epithelia. To determine whether modulation of the basolateral K+ conductance would result in parallel changes in apical Na+ conductance and basolateral pump activity, Necturus urinary bladders stripped of serosal muscle and connective tissue were impaled through their basolateral membranes with microelectrodes in experiments that allowed rapid serosal solution changes. Exposure of the basolateral membrane to the K+ channel blockers Ba2+ (0.5 mM/liter), Cs+ (10 mM/liter), or Rb+ (10 mM/liter) increased the basolateral resistance (Rb) by greater than 75% in each case. The increases in Rb were accompanied simultaneously by significant increases in apical resistance (Ra) of greater than 20% and decreases in transepithelial Na+ transport. The increases in Ra, measured as slope resistances, cannot be attributed to nonlinearity of the I-V relationship of the apical membrane, since the measured cell membrane potentials with the K+ channel blockers present were not significantly different from those resulting from increasing serosal K+, a maneuver that did not affect Ra. Thus, blocking the K+ conductance causes a reduction in net Na+ transport by reducing K+ exit from the cell and simultaneously reducing Na+ entry into the cell. Close correlations between the calculated short-circuit current and the apical and basolateral conductances were preserved after the basolateral K+ conductance pathways had been blocked. Thus, the interaction between the basolateral and apical conductances revealed by blocking the basolateral K+ channels is part of a network of feedback relationships that normally serves to maintain cellular homeostasis during changes in the rate of transepithelial Na+ transport.

Amiloride↗

PubMed1987

Interactions of sodium transport, cell volume, and calcium in frog urinary bladder.

The volume of individual cells in intact frog urinary bladders was determined by quantitative microscopy and changes in volume were used to monitor the movement of solute across the basolateral membrane. When exposed to a serosal hyposmotic solution, the cells swell as expected for an osmometer, but then regulate their volume back to near control in a process that involves the loss of KCl. We show here that volume regulation is abolished by Ba++, which suggests that KCl movements are mediated by conductive channels for both ions. Volume regulation is also inhibited by removing Ca++ from the serosal perfusate, which suggests that the channels are activated by this cation. Previously, amiloride was observed to inhibit volume regulation: in this study, amiloride-inhibited, hyposmotically swollen cells lost volume when the Ca++ ionophore A23187 was added to Ca++-replete media. We attempted to effect volume changes under isosmotic conditions by suddenly inhibiting Na+ entry across the apical membrane with amiloride, or Na+ exit across the basolateral membrane with ouabain. Neither of these Na+ transport inhibitors produced the expected results. Amiloride, instead of causing a decrease in cell volume, had no effect, and ouabain, instead of causing cell swelling, caused cell shrinkage. However, increasing cell Ca++ with A23187, in both the absence and presence of amiloride, caused cells to lose volume, and Ca++-free Ringer's solution (serosal perfusate only) caused ouabain-blocked cells to swell. Finally, again under isosmotic conditions, removal of Na+ from the serosal perfusate caused a loss of volume from cells exposed to amiloride. These results strongly suggest that intracellular Ca++ mediates cell volume regulation by exerting a negative control on apical membrane Na+ permeability and a positive control on basolateral membrane K+ permeability. They also are compatible with the existence of a basolateral Na+/Ca++ exchanger.

Animals↗

PubMed1985

Effects of intracellular sodium and potassium iontophoresis on membrane potentials and resistances in toad urinary bladder.

Glass microelectrodes were used to measure membrane potentials and the ratio of apical to basolateral membrane resistances before and after the passage of current from the potential-recording microelectrode to ground, in toad urinary bladder epithelium, in order to iontophorese cations into the cell. After application of the current, there was a transient change in the tip potential of the microelectrode. This artifact was measured with the microelectrode in the mucosal medium and was subtracted from the potential recorded in the cell. The serosal medium was bathed by Ringer's solution containing 51.5 mM K+ to minimize any current-induced increase of K+ in the unstirred layer. Under those conditions, both Na+ and K+ iontophoresis caused a significant hyperpolarization of basolateral membrane potential (Vcs) and a significant increase in the ratio of apical to basolateral membrane resistances (Ra/Rb). When bladders were exposed to amiloride in the mucosal solution, Na+ iontophoresis caused the basolateral membrane to hyperpolarize, but no significant changes were observed in Ra/Rb. When Na+ was injected in the presence of serosal ouabain, Vcs depolarized and Ra/Rb increased. K+ iontophoresis caused the basolateral membrane potential to hyperpolarize in the presence of ouabain but Ra/Rb did not change significantly. These results indicate that the Na+ pump in toad bladder is rheogenic, that apical Na+ conductance is sensitive to the cell levels of Na+ and K+ and that the basolateral membrane is K+ permeable.

Amiloride↗

PubMed1985

Effects of mucosal sodium removal on cell volume in Necturus gallbladder epithelium.

Necturus gallbladder epithelium transports sodium and chloride by a process that first involves the cellular entry of each ion across the apical membrane in an electrically silent process. In this paper we present results from cell volume and fluid flux measurements in the presence of different inhibitors and at normal and reduced sodium concentrations, which bear on the process by which ionic entry is effected. We find that reduction of mucosal sodium to a concentration of 10 mM has no effect on either cell volume or on the rate of transepithelial fluid transport, whereas the complete removal of sodium causes a significant decrease in cell volume in addition to its known inhibitory effect on fluid transport. Amiloride had no effect on cell volume at normal sodium concentrations but markedly reduced it when the sodium concentration was reduced to 10 mM. Amiloride, bumetanide, and dipyridamole markedly and reversibly inhibited fluid transport. Finally, the addition of ouabain to the serosal medium induced cell swelling, which was prevented by the removal of potassium from the mucosal medium. These results indicate that the process of sodium entry at the apical membrane is complicated and likely includes both cotransport (NaCl or Na-K-2Cl) and parallel exchange (Na-H and Cl-HCO3) transport mechanisms, and that the proportion of NaCl transported by the different mechanisms varies with the conditions.

Amiloride↗