ML133 HCl: Selective Kir2.1 Channel Blocker for Cardiovascular Ion Channel Research

Executive Summary: ML133 HCl is a potent and selective inhibitor of Kir2.1 potassium channels, with an IC50 of 1.8 μM at pH 7.4 and 290 nM at pH 8.5, showing negligible inhibition of Kir1.1 and weak activity against Kir4.1 and Kir7.1 channels (Cao et al., 2022). This compound is insoluble in water but is readily dissolved in DMSO (≥15.7 mg/mL) and ethanol (≥2.52 mg/mL) under mild heating or ultrasonic conditions (ApexBio). ML133 HCl is widely employed in studies on pulmonary artery smooth muscle cell (PASMC) proliferation and migration, making it valuable for cardiovascular disease modeling. Recent research demonstrates its ability to inhibit the TGF-β1/SMAD2/3 pathway and suppress PASMC proliferation and migration. ML133 HCl, supplied as a solid and stable at -20°C, is a cornerstone reagent for investigators examining Kir2.1 channel function and its role in vascular remodeling.

Biological Rationale

Potassium channels regulate cellular excitability and maintain membrane potential in excitable tissues. The Kir2.1 channel, coded by the KCNJ2 gene, is a classical inwardly rectifying potassium channel crucial for maintaining resting membrane potential in cardiac and vascular smooth muscle cells (Cao et al., 2022). Dysregulation of Kir2.1 contributes to pathological vascular remodeling processes observed in pulmonary hypertension, where excessive proliferation and migration of PASMCs drive disease progression. Targeted inhibition of Kir2.1 channels with ML133 HCl enables precise study of potassium ion transport and its downstream effects on cell signaling, proliferation, and migration. This specificity is vital for dissecting the mechanistic pathways involved in cardiovascular diseases while minimizing off-target effects on related potassium channels.

Mechanism of Action of ML133 HCl

ML133 HCl acts as a competitive and selective inhibitor of the Kir2.1 channel, with minimal cross-reactivity to Kir1.1 and only weak inhibition of Kir4.1 and Kir7.1 at tested concentrations (ApexBio). The hydrochloride salt form, 1-(4-methoxyphenyl)-N-(naphthalen-1-ylmethyl)methanamine·HCl, with a molecular weight of 313.82 and formula C₁₉H₁₉NO·HCl, blocks potassium ion conductance through Kir2.1 by binding to the channel pore region. In cellular assays, ML133 HCl reverses the proliferative and migratory effects induced by platelet-derived growth factor (PDGF)-BB in PASMCs, in part by suppressing upregulation of proliferation markers (OPN, PCNA) and inhibiting the TGF-β1/SMAD2/3 signaling pathway (Cao et al., 2022). This mechanistic specificity allows researchers to attribute observed cellular effects directly to Kir2.1 inhibition.

Evidence & Benchmarks

• ML133 HCl inhibits Kir2.1 channels with an IC50 of 1.8 μM at pH 7.4 and 290 nM at pH 8.5 (ApexBio).
• ML133 HCl exhibits no inhibitory effect on Kir1.1 and only weak activity against Kir4.1 and Kir7.1 channels at equivalent concentrations (ApexBio).
• In human PASMCs, ML133 HCl reverses PDGF-BB-induced proliferation and migration by suppressing OPN and PCNA expression and inhibiting the TGF-β1/SMAD2/3 pathway (Cao et al., 2022).
• In rat models of pulmonary hypertension, Kir2.1 channel activity is upregulated in the pulmonary vasculature, and its inhibition reduces pathological vascular remodeling (Cao et al., 2022).
• ML133 HCl is insoluble in water but dissolves in DMSO (≥15.7 mg/mL) and ethanol (≥2.52 mg/mL) with gentle warming and ultrasonic treatment (ApexBio).

This article extends the mechanistic and application detail found in 'Targeting Kir2.1 Potassium Channels: Mechanistic Insights' by providing updated benchmarks from the 2022 peer-reviewed data and offering practical workflow integration guidance. For a broader context on solubility and protocol compatibility, see 'ML133 HCl: Selective Kir2.1 Channel Blocker for Cardiovas...', which is clarified here with more precise IC50 data and storage limitations.

Applications, Limits & Misconceptions

ML133 HCl is primarily used to study the role of Kir2.1 channels in cardiovascular and pulmonary research, including:

• Modeling pulmonary hypertension and vascular remodeling in animal and cell culture systems.
• Investigating the molecular mechanisms of PASMC proliferation and migration.
• Screening for potential therapeutic targets in cardiovascular disease models.
• Validating the specificity of Kir2.1 involvement in potassium ion transport and downstream signaling.

Common Pitfalls or Misconceptions

• ML133 HCl is not effective against Kir1.1 channels and should not be used to study these targets (ApexBio).
• Long-term storage of ML133 HCl in solution is not recommended due to limited stability; always prepare fresh aliquots for experiments (ApexBio).
• ML133 HCl is insoluble in water and must be dissolved in DMSO or ethanol for biological assays (ApexBio).
• Observed effects on vascular remodeling are attributable to Kir2.1 inhibition; off-target effects are minimal but possible at very high concentrations.
• ML133 HCl does not directly inhibit the TGF-β1/SMAD2/3 pathway; its effect is mediated via Kir2.1 blockade (Cao et al., 2022).

Workflow Integration & Parameters

ML133 HCl is supplied as a solid and should be stored at -20°C for optimal stability. For experimental use, dissolve in DMSO (≥15.7 mg/mL) or ethanol (≥2.52 mg/mL) with gentle warming or ultrasonic treatment. Avoid repeated freeze-thaw cycles and prepare working solutions fresh before each use. Typical working concentrations range from 0.3 to 10 μM, depending on assay design and desired selectivity. Use sterile filtration where appropriate. ML133 HCl is compatible with a wide range of in vitro and in vivo protocols for cardiovascular research. For detailed protocol guidance, refer to the product page for ML133 HCl (B2199). For further insights on integrating this inhibitor into advanced cardiovascular models, see 'ML133 HCl: Advancing Precision in Kir2.1 Channel Modulation', which is expanded here with newly validated application benchmarks and solubility data.

Conclusion & Outlook

ML133 HCl is a rigorously validated, selective Kir2.1 channel inhibitor that enables precise dissection of potassium ion transport and regulation in cardiovascular disease models. Its well-characterized mechanism of action, robust selectivity profile, and solubility in research-compatible solvents make it indispensable for PASMC and vascular remodeling studies. Future research may leverage ML133 HCl for translational breakthroughs in pulmonary hypertension and related disorders, with ongoing refinement of application protocols and cross-validation in new disease models. For comprehensive product specifications and ordering information, visit the ML133 HCl product page.