Amiloride (MK-870): Atomic Insights for Sodium Channel and Endocytosis Research

Executive Summary: Amiloride (MK-870), supplied by APExBIO, is an established epithelial sodium channel (ENaC) and urokinase-type plasminogen activator receptor (uPAR) inhibitor with a molecular weight of 229.63 g/mol and formula C₆H₈ClN₇O. It modulates sodium influx in epithelial models and blocks PC2 channels, supporting research in hypertension, cystic fibrosis, and cellular uptake mechanisms (internal). Peer-reviewed studies confirm that Amiloride does not inhibit clathrin-mediated endocytosis of type III grass carp reovirus in kidney cells, establishing boundaries for its utility (Wang et al. 2018). The compound must be stored at -20°C and is not intended for clinical or diagnostic use. This guide provides atomic, evidence-based claims and workflow parameters for reliable deployment in sodium channel and endocytosis research.

Biological Rationale

Amiloride (MK-870) selectively inhibits epithelial sodium channels (ENaC), modulating sodium reabsorption in epithelial tissues (internal). It is also a recognized inhibitor of the urokinase-type plasminogen activator receptor (uPAR), impacting cellular migration and signal transduction. The dual-action mechanism supports investigations into sodium transport disorders (e.g., cystic fibrosis, hypertension), as well as cellular uptake and endocytosis processes (internal). Amiloride is used in both basic research and translational models to map the role of ENaC/uPAR in pathophysiological states.

Mechanism of Action of Amiloride (MK-870)

Amiloride (MK-870) directly blocks epithelial sodium channels by binding to ENaC at the extracellular domain, inhibiting sodium influx across the apical membrane of epithelial cells. This action reduces sodium reabsorption and modulates membrane potential. The compound also antagonizes uPAR, interfering with receptor-mediated cellular migration and signaling cascades. As a PC2 channel blocker, Amiloride influences calcium and sodium homeostasis. These combined actions enable targeted modulation of ion transport and cellular signaling pathways relevant to sodium channel research and cellular endocytosis studies (internal).

Evidence & Benchmarks

• Amiloride (MK-870) inhibits ENaC-mediated sodium currents in epithelial cells with an IC₅₀ typically in the low micromolar range under physiological buffer conditions (see internal for specific assay data).
• Amiloride does not inhibit clathrin-mediated endocytosis of type III grass carp reovirus (GCRV104) in CIK cells, as shown in pharmacological inhibitor studies (Wang et al. 2018, https://doi.org/10.1186/s12985-018-0993-8).
• In cell viability and cytotoxicity assays, Amiloride (MK-870) demonstrates consistent performance, provided solution stability is maintained (internal).
• PC2 channel blocking by Amiloride alters calcium and sodium fluxes in renal epithelial models, supporting its use in ion transport research (internal).
• Amiloride is not effective in blocking dynamin-dependent or pH-dependent viral entry in GCRV-infected CIK cells, clarifying its mechanistic specificity (Wang et al. 2018, https://doi.org/10.1186/s12985-018-0993-8).

Applications, Limits & Misconceptions

Amiloride (MK-870) is widely used in:

• Epithelial sodium channel research, including models of hypertension and cystic fibrosis.
• Cellular endocytosis modulation, specifically for studying ENaC and uPAR-dependent uptake pathways.
• Ion transport and signaling pathway mapping in renal, pulmonary, and epithelial models.
• Cell viability, proliferation, and cytotoxicity assay workflows, where sodium channel blockade is a critical parameter (internal).

For a deeper mechanistic and translational strategy, see this article, which this dossier extends by providing updated benchmarks and explicit non-inhibition data for viral endocytosis.

Common Pitfalls or Misconceptions

• Not a universal endocytosis inhibitor: Amiloride does not inhibit clathrin-mediated or dynamin-dependent endocytosis in all models (Wang et al. 2018, DOI).
• Not effective against all viral entry routes: It does not block GCRV104 entry in CIK cells, unlike ammonium chloride or dynasore.
• Not a long-term stock solution: Amiloride solutions degrade; use promptly after preparation for reproducibility (APExBIO).
• Not for clinical or diagnostic use: Research use only, not for human/animal therapeutic applications.
• Mechanistic specificity is critical: It targets ENaC/uPAR but not all ion or receptor types.

Workflow Integration & Parameters

Amiloride (MK-870) is supplied as a solid by APExBIO (product page), molecular weight 229.63 g/mol, formula C₆H₈ClN₇O. Best practices include:

• Store at -20°C in a desiccated environment.
• Reconstitute in DMSO or compatible aqueous buffer immediately before use; avoid prolonged storage of stock solutions.
• Employ in sodium channel assays at concentrations validated in published protocols (e.g., 1–100 μM, depending on cell model and endpoint).
• Use with cell viability, proliferation, and cytotoxicity assays per scenario-driven guides (internal).
• Ship with Blue Ice for small molecules or Dry Ice for modified nucleotides, per APExBIO specifications.

This article clarifies the evidence base and workflow parameters, expanding on the mechanistic focus in this prior review by including negative controls and stability data.

Conclusion & Outlook

Amiloride (MK-870, BA2768) is a validated ENaC and uPAR inhibitor, supporting ion channel and endocytosis research in academic and translational settings. Its mechanistic specificity is now well defined, as it does not broadly inhibit clathrin-mediated endocytosis or all viral entry routes. Proper storage and prompt use of solutions are essential for experimental reliability. These atomic, evidence-based parameters enable researchers to confidently deploy Amiloride (MK-870) from APExBIO in sodium channel and cellular uptake studies, while recognizing its boundaries and optimal applications.