Amiloride (MK-870): Epithelial Sodium Channel Inhibitor for Advanced Ion Channel Research

Executive Summary: Amiloride (MK-870) is a potent inhibitor of epithelial sodium channels (ENaC) and urokinase-type plasminogen activator receptors (uPAR), with a defined molecular weight of 229.63 g/mol and formula C₆H₈ClN₇O (APExBIO). It is widely used in sodium channel research, cystic fibrosis, and hypertension models due to its high specificity and rapid action (Geier et al., 2024). Amiloride's stability is optimal at -20°C and solutions should be freshly prepared before use. The compound enables discrimination between ENaC- and uPAR-mediated signaling in cell-based assays. Its role in modulating cellular endocytosis and benchmarking ion channel blockers is well-established in peer-reviewed literature.

Biological Rationale

Amiloride (MK-870) is a pyrazine-carboxamide derivative that selectively inhibits epithelial sodium channels (ENaC) in mammalian tissues (APExBIO). The ENaC pathway is critical in regulating sodium and water homeostasis in epithelial cells, especially in the kidney, lung, and colon. Dysregulation of ENaC activity contributes to diseases such as cystic fibrosis and hypertension (see related article). Amiloride also inhibits urokinase-type plasminogen activator receptor (uPAR), impacting cell adhesion, migration, and proliferation. This dual-targeting mechanism is essential for dissecting complex signaling networks in epithelial biology. By serving as a reference compound for ENaC and uPAR blockade, Amiloride advances mechanistic studies in ion transport and receptor-mediated endocytosis.

Mechanism of Action of Amiloride (MK-870)

Amiloride (MK-870) acts by binding to the extracellular domain of ENaC, thereby inhibiting sodium ion influx across epithelial membranes. This block is dose-dependent, reversible, and occurs at micromolar concentrations (IC₅₀ typically 0.1–10 µM, depending on species and cell type; see mechanistic update). By preventing sodium reabsorption, Amiloride indirectly modulates downstream signaling cascades, including those involving intracellular calcium and cyclic AMP. Independent of ENaC, Amiloride inhibits uPAR-mediated processes, affecting cell surface proteolysis and migration. Additionally, Amiloride is reported as a PC2 channel blocker, enabling the study of polycystic kidney disease models. Its effects are rapid, with maximal inhibition achieved within minutes at 37°C in standard physiological buffers. Amiloride does not covalently modify its targets, allowing for reversible experimental control. The dual action on ENaC and uPAR is unique among small-molecule inhibitors and is central to its value in advanced cell signaling assays.

Evidence & Benchmarks

• Amiloride (MK-870) inhibits ENaC currents in Xenopus oocytes by >90% at 10 µM, as measured by two-electrode voltage clamp (DOI).
• In human airway epithelial cells, Amiloride reduces sodium transport by 80% within 10 minutes at 37°C in HEPES-buffered saline (internal source).
• Amiloride blocks uPAR-mediated cellular migration in in vitro wound healing assays, with maximal inhibition at 50 µM (internal source).
• The compound's storage stability at -20°C ensures >98% purity for at least 12 months as a solid (APExBIO).
• Amiloride does not significantly inhibit voltage-gated sodium channels (Nav1.5) at concentrations <100 µM, supporting its selectivity for ENaC (internal source).

Applications, Limits & Misconceptions

Amiloride (MK-870) is primarily deployed in research on sodium channel function, epithelial transport, and receptor-mediated endocytosis. It is a reference inhibitor for benchmarking new ENaC-targeting agents in cystic fibrosis and hypertension research (BA2768 kit). Its use extends to in vitro and ex vivo models, including patch clamp, Ussing chamber, and cell migration assays. In contrast to other articles—such as this mechanistic review, which details selectivity—this article provides a comprehensive integration of stability, workflow, and benchmarking for experimental reproducibility.

Recent literature highlights its role in dissecting endocytosis mechanisms and validating uPAR as a research target (detailed analysis). Amiloride is not suitable for voltage-gated sodium channel studies or as a therapeutic agent, reflecting its specificity and research-only designation. The compound is not recommended for long-term solution storage; fresh preparation is essential for reproducible results.

Common Pitfalls or Misconceptions

• Not a pan-sodium channel blocker: Amiloride is selective for ENaC and does not inhibit voltage-gated sodium channels (Nav), which are structurally distinct.
• Not suitable for chronic in vivo experiments: Due to poor metabolic stability and short plasma half-life, Amiloride is not ideal for long-term animal studies without modification.
• Not for therapeutic or diagnostic use: This compound is for research use only; it is not approved for human or veterinary therapy.
• Sensitivity to storage conditions: Solutions degrade rapidly at room temperature; always prepare fresh aliquots and store at -20°C as a solid.
• Concentration-dependent off-targets: At concentrations >100 µM, off-target effects on other ion channels may occur; use recommended ranges for specificity.

Workflow Integration & Parameters

Amiloride (MK-870) from APExBIO is supplied as a solid, 10–50 mg quantity, with shipping in Blue Ice to maintain integrity. For in vitro experiments, dissolve in DMSO or physiological saline to desired concentration (e.g., 1–100 µM). Use in cell-based assays, patch clamp, or Ussing chamber setups. Prepare solutions immediately before use; do not store long-term. The compound is compatible with standard buffers (pH 7.2–7.4) and can be combined with fluorescent reporters for real-time sodium flux assays. For benchmarking, compare with other ENaC blockers, ensuring all conditions (temperature, time, buffer) are matched (internal guide).

Shipping parameters: Blue Ice for small molecules, Dry Ice for nucleotides. Store at -20°C upon receipt. Record batch and date for reproducibility. For detailed workflow integration, see this strategy-focused article, which maps advanced use cases and competitive benchmarking steps. This article extends that guidance by integrating explicit stability and storage protocols for optimal performance.

Conclusion & Outlook

Amiloride (MK-870) remains the gold standard for studying ENaC and uPAR pathways, with applications spanning epithelial transport, cystic fibrosis, and hypertension models. Its defined mechanism, rapid action, and benchmarked selectivity make it indispensable in mechanistic and translational research. As new ENaC and uPAR modulators are developed, Amiloride will continue to serve as a primary reference compound. For detailed product information and ordering, consult the APExBIO Amiloride (MK-870) page. This article provides a comprehensive, atomic, and verifiable resource for optimizing sodium channel research workflows.