Amiloride (MK-870): Atomic Profile of an Epithelial Sodium Channel Inhibitor

Executive Summary: Amiloride (MK-870) is a potent and selective inhibitor of epithelial sodium channels (ENaC) and urokinase-type plasminogen activator receptors (uPAR), widely used in sodium channel research and cellular endocytosis studies (APExBIO). It exhibits a molecular weight of 229.63 Da and a chemical formula of C₆H₈ClN₇O. The compound is stable at -20°C and rapidly loses potency in solution, necessitating prompt usage after preparation. Amiloride's mechanistic specificity is benchmarked in both ion transport assays and receptor signaling models (Geier et al., 2024). Its research-only designation ensures rigorous standards for experimental reproducibility and excludes diagnostic or therapeutic use.

Biological Rationale

Ion channels, particularly the epithelial sodium channel (ENaC), regulate sodium transport across cellular membranes, impacting physiological processes such as fluid balance, blood pressure, and mucociliary clearance (see detailed mechanism). Amiloride (MK-870) is used to dissect ENaC's role in pathologies like cystic fibrosis and hypertension by modulating sodium influx at the channel level. The urokinase-type plasminogen activator receptor (uPAR) is involved in cell signaling and migration; its inhibition by Amiloride aids in studies of endocytosis and receptor-mediated signaling. This article extends practical laboratory perspectives found in scenario-driven guides by providing atomic, citation-backed claims for systematic knowledge extraction.

Mechanism of Action of Amiloride (MK-870)

Amiloride (MK-870) acts by selectively blocking ENaC, thereby reducing transmembrane sodium flux. This inhibition occurs at low micromolar concentrations, with reported IC₅₀ values typically in the range of 0.1–10 μM, depending on cell type and assay conditions (see advanced modulation details). The molecule also antagonizes uPAR, affecting downstream signaling pathways such as ERK phosphorylation and cellular migration. As a PC2 channel blocker, Amiloride modulates additional ion transport processes, expanding its utility in mechanistic studies of cell signaling. These dual activities enable the compound to serve as a molecular probe for dissecting both channel- and receptor-mediated events.

Evidence & Benchmarks

• Amiloride inhibits ENaC-mediated sodium currents in epithelial cell models, with IC₅₀ values between 0.1 and 10 μM, under physiological pH and ionic strength (Geier et al., 2024).
• It effectively blocks uPAR-mediated cell migration in vitro, as shown by reduced ERK phosphorylation and wound healing assays (see mechanistic impact).
• In cystic fibrosis airway epithelial models, Amiloride reduces sodium hyperabsorption and increases mucus hydration (evidence-based claims).
• Amiloride is stable as a solid at -20°C for at least 12 months; in aqueous solution, functional activity declines by 50% within 24 hours at room temperature (APExBIO technical data).
• It shows no significant inhibition of potassium or calcium channels at concentrations effective for ENaC blockade, minimizing off-target effects (Geier et al., 2024).

Applications, Limits & Misconceptions

Amiloride (MK-870) is primarily applied in:

• Sodium channel research, including ENaC function studies and disease modeling in cystic fibrosis (unraveling ENaC and uPAR inhibition).
• Cellular endocytosis research, where its inhibition of uPAR provides insights into receptor signaling pathways.
• Hypertension research, as a tool compound for dissecting renal sodium handling mechanisms.
• Benchmarking cell viability, proliferation, and cytotoxicity assays in ion channel studies (scenario-driven best practices).

This article clarifies molecular storage, use timing, and cross-channel selectivity relative to prior resources, offering explicit stability and cross-reactivity data for reproducible research.

Common Pitfalls or Misconceptions

• Amiloride (MK-870) is not suitable for diagnostic or therapeutic use in humans—research use only, as designated by APExBIO.
• Its inhibitory effect is limited to ENaC and uPAR at effective concentrations; it does not inhibit all sodium channels or general ion transporters.
• Solutions are unstable at room temperature; activity drops significantly after 24 hours in aqueous buffer.
• Long-term storage in solution is not recommended; always prepare fresh solutions immediately before use.
• Amiloride does not correct underlying genetic defects in disease models (e.g., CFTR mutations in cystic fibrosis) but modulates downstream ion transport.

Workflow Integration & Parameters

Amiloride (MK-870) is supplied as a solid and should be dissolved in DMSO or water immediately prior to use. Store at -20°C to maintain activity. For cell-based assays, typical working concentrations range from 0.1–10 μM, and exposure times should be standardized (30–60 minutes) to limit variability. Shipping is performed with Blue Ice for small molecules or Dry Ice for modified nucleotides. For reproducible results, avoid repeated freeze-thaw cycles and discard unused solution after each experiment. The BA2768 kit from APExBIO provides certified documentation and batch traceability.

Conclusion & Outlook

Amiloride (MK-870) remains a gold-standard reagent for dissecting ENaC and uPAR function in sodium channel and receptor signaling research. Its well-defined mechanism, strict stability requirements, and specificity have made it indispensable in both fundamental ion transport studies and disease modeling. Future developments may extend its platform for high-throughput screening or personalized medicine applications, but its current use is limited to research settings. For further guidance on integration into complex workflows, see related articles that address scenario-driven best practices and assay optimization (lab challenges guide).