Amiloride (MK-870): Research-Grade Epithelial Sodium Channel Inhibitor for Mechanistic and Translational Studies

Executive Summary: Amiloride (MK-870) is an established inhibitor of epithelial sodium channels (ENaC) and urokinase-type plasminogen activator receptors (uPAR), enabling specific modulation of ion transport and cellular uptake mechanisms (Wang et al. 2018, DOI). The compound is supplied by APExBIO (SKU BA2768) as a solid (MW 229.63, C6H8ClN7O) and is intended for research use only (product page). Amiloride is stable at -20°C; solutions should be freshly prepared due to limited shelf stability. Its selective ENaC blockade underpins its utility in dissecting sodium channel signaling, ion transport, and mechanisms underlying diseases like cystic fibrosis and hypertension (Chempaign.net). In validated cellular models, Amiloride does not inhibit clathrin-mediated endocytosis of reoviruses, delineating its mechanistic boundaries (Wang et al. 2018, DOI).

Biological Rationale

Amiloride (MK-870) is a pyrazine derivative that acts as a potent and selective inhibitor of the epithelial sodium channel (ENaC), a membrane protein complex critical for sodium ion (Na⁺) reabsorption in epithelial tissues. ENaC activity regulates extracellular fluid volume, blood pressure, and airway surface liquid composition, with direct implications for cystic fibrosis and hypertension research (Chempaign.net). Amiloride also inhibits the urokinase-type plasminogen activator receptor (uPAR), which is implicated in cellular adhesion and signaling pathways. The specificity of Amiloride enables targeted investigation of sodium channel function without directly affecting other endocytic or ion transport pathways (Wang et al. 2018, DOI).

Mechanism of Action of Amiloride (MK-870)

Amiloride blocks ENaC by binding to its extracellular domain, resulting in competitive inhibition of Na⁺ influx. This inhibition occurs at micromolar concentrations (typically 1–100 µM) under physiological pH (7.4) and temperature (37°C) conditions. The blockade is reversible and non-covalent. Amiloride also antagonizes the urokinase-type plasminogen activator receptor, interfering with downstream proteolytic and signaling events (Dynamin-Inhibitory-Peptide.com). Additionally, Amiloride can inhibit PC2 channels and modulate cellular uptake mechanisms, but does not significantly interfere with clathrin-mediated endocytosis in reovirus infection models (Wang et al. 2018, DOI).

Evidence & Benchmarks

• Amiloride blocks ENaC-mediated sodium transport in epithelial cells at concentrations ≥1 µM, with >80% inhibition in vitro under standard buffer conditions (pH 7.4, 37°C) (Chempaign.net).
• Amiloride does not impede clathrin-mediated endocytosis of type III grass carp reovirus, demonstrating pathway specificity (Wang et al. 2018, DOI).
• In comparative cell viability and proliferation assays, Amiloride (MK-870, BA2768) displays superior reproducibility over non-specific sodium channel inhibitors (Phosphatase-Inhibitor.com).
• Amiloride solutions rapidly lose activity above 4°C or after 24 hours post-dissolution, supporting the recommendation for prompt use (APExBIO product page).
• Amiloride's effect on cellular uptake is limited to ENaC/uPAR pathways; it does not affect dynamin-dependent or actin-dependent entry mechanisms (Wang et al. 2018, DOI).

This article clarifies the mechanistic boundary of Amiloride in endocytosis, extending prior guidance (Phosphatase-Inhibitor.com) by distinguishing ENaC/uPAR specificity from broader endocytic inhibition.

Applications, Limits & Misconceptions

Amiloride (MK-870) is integral to research in:

• Sodium Channel Research: Dissecting ENaC-mediated ion transport in kidney, lung, and airway models.
• Cellular Endocytosis Modulation: Probing the role of ENaC/uPAR in cellular uptake without off-target effects on clathrin-mediated pathways (Wang et al. 2018).
• Cystic Fibrosis and Hypertension Models: Modeling disease mechanisms through ENaC inhibition.
• Benchmarking Reproducibility: Supporting standardized workflows in cytotoxicity and proliferation assays (MK-0822.com).

This article updates mechanistic insight detailed in Chempaign.net by integrating recent evidence on endocytosis boundaries.

Common Pitfalls or Misconceptions

• Amiloride does not inhibit clathrin-mediated endocytosis: Wang et al. (2018) demonstrate no effect on reovirus entry, clarifying a common misapplication in endocytosis research (DOI).
• Short solution stability: Amiloride loses potency rapidly after dissolution; avoid long-term storage of solutions (APExBIO).
• Not a pan-endocytosis inhibitor: Amiloride's effect is restricted to ENaC/uPAR; it does not block dynamin-dependent, actin-dependent, or caveolin-mediated uptake (DOI).
• Research use only: Product BA2768 is not for diagnostic or therapeutic application (APExBIO).
• Temperature sensitivity: Activity is compromised above 4°C; all experiments should use freshly prepared, cold-stored solutions.

Workflow Integration & Parameters

Amiloride (MK-870, SKU BA2768) is supplied as a white to off-white solid, molecular weight 229.63 g/mol, chemical formula C6H8ClN7O. Store at -20°C for stability. Prepare solutions fresh in appropriate solvent (e.g., DMSO or aqueous buffer), use within 24 hours, and avoid freeze-thaw cycles. For in vitro studies, working concentrations range from 1–100 µM depending on model system. Shipping is performed with Blue Ice (small molecules) or Dry Ice (modified nucleotides), according to APExBIO guidelines (product page). For optimized assay reliability, consult scenario-driven strategies in MK-0822.com, which this article extends by providing updated specificity data from recent peer-reviewed research.

Conclusion & Outlook

Amiloride (MK-870) remains a cornerstone tool for mechanistic sodium channel and uPAR research. Its high specificity, defined stability profile, and extensive benchmarking ensure reproducible results in translational workflows. APExBIO’s BA2768 product is optimized for research utility, with detailed mechanistic boundaries now clarified by recent studies. Future directions include refined applications in disease modeling and combinatorial pathway investigations. For full product specifications, see the Amiloride (MK-870) product page.