ML133 HCl: Selective Kir2.1 Potassium Channel Inhibitor

Executive Summary: ML133 HCl is a solid-phase, highly selective inhibitor of Kir2.1 potassium channels, demonstrating an IC50 of 1.8 μM at pH 7.4 and 290 nM at pH 8.5 according to the product data. The compound exhibits negligible inhibition of Kir1.1 and only weak activity against Kir4.1 and Kir7.1. ML133 HCl has been validated for suppressing pulmonary artery smooth muscle cell (PASMC) proliferation and migration in vitro, implicating Kir2.1 as a target for pulmonary vascular remodeling, as shown in peer-reviewed studies (Cao et al., 2022). Provided by APExBIO, ML133 HCl is supplied at ≥98% purity and is soluble in DMSO and ethanol, but not water, under recommended storage at -20°C.

Biological Rationale

Potassium channels are fundamental in setting the membrane potential and regulating excitability in diverse cell types. The inwardly rectifying potassium channel Kir2.1, encoded by the KCNJ2 gene, is particularly crucial in cardiovascular tissues and smooth muscle cells. Dysregulation of Kir2.1 has been linked to pathological cellular proliferation and migration, notably in the context of pulmonary artery smooth muscle cell (PASMC) involvement in pulmonary hypertension and vascular remodeling (Cao et al., 2022). Experimental evidence indicates that Kir2.1 upregulation is associated with enhanced PASMC proliferation and migration, which are hallmark features of pulmonary vascular remodeling (Kir2.1 Inhibition Reduces PASMC Proliferation and Migration). This article extends previous analyses by quantifying the selectivity and mechanistic specificity of ML133 HCl in these cellular models.

Mechanism of Action of ML133 HCl

ML133 HCl acts as a potent and selective blocker of Kir2.1 channels. The compound binds to the channel pore, inhibiting potassium ion transport in a pH-dependent manner. At physiological pH 7.4, the half-maximal inhibitory concentration (IC50) is 1.8 μM, while at more alkaline pH 8.5, the IC50 decreases to 290 nM, indicating increased potency under these conditions (APExBIO). The selectivity profile is robust: ML133 HCl does not inhibit Kir1.1 and only weakly inhibits Kir4.1 and Kir7.1, minimizing off-target effects (ML133 HCl: Precision Inhibition of Kir2.1 in Pulmonary Research). This high specificity enables researchers to dissect the role of Kir2.1-mediated potassium ion transport without confounding activity from closely related channels.

Evidence & Benchmarks

• ML133 HCl inhibits Kir2.1 potassium channels with an IC50 of 1.8 μM at pH 7.4 and 290 nM at pH 8.5, as verified in recombinant expression systems (APExBIO).
• The compound exhibits <10% inhibition of Kir1.1, Kir4.1, and Kir7.1 at concentrations up to 10 μM, confirming its selectivity (ML133 HCl: Precision Kir2.1 Potassium Channel Inhibitor).
• ML133 HCl suppresses PDGF-BB-induced PASMC proliferation and migration in vitro, reversing upregulation of osteopontin (OPN) and proliferating cell nuclear antigen (PCNA) and inhibiting the TGF-β1/SMAD2/3 pathway (Cao et al., 2022).
• ML133 HCl demonstrates excellent solubility in DMSO (≥15.7 mg/mL) and ethanol (≥2.52 mg/mL) with gentle warming and sonication; it is insoluble in water (APExBIO).
• ML133 HCl is supplied at ≥98% purity, confirmed by HPLC and NMR, supporting reproducibility in cardiovascular ion channel research (ML133 HCl: Reliable Kir2.1 Inhibition in PASMC Assays).

Applications, Limits & Misconceptions

ML133 HCl is a cornerstone tool in pulmonary artery smooth muscle cell proliferation research and cardiovascular ion channel studies. By enabling selective inhibition of Kir2.1, it helps define the specific contribution of this channel to pathological cell growth and migration, vital for pulmonary hypertension and vascular remodeling models (ML133 HCl: Precision Targeting of Kir2.1 in Vascular Remodeling). This article clarifies the boundaries of ML133 HCl's selectivity and operational parameters, building on prior internal analyses.

Common Pitfalls or Misconceptions

• Not a pan-potassium channel blocker: ML133 HCl is highly selective for Kir2.1 and does not significantly inhibit other Kir channels at recommended concentrations (APExBIO).
• Water insolubility: Direct dissolution in aqueous buffers is ineffective; DMSO or ethanol with gentle warming and sonication is required.
• Not suitable for long-term solution storage: Stability of ML133 HCl solutions declines over time; fresh preparation is recommended for each experiment.
• In vivo use limitations: Most efficacy evidence pertains to in vitro or ex vivo PASMC models; in vivo pharmacokinetics and bioavailability require further study.
• No effect on Kir1.1: ML133 HCl should not be used to probe Kir1.1 function, as it lacks significant inhibitory activity on this channel subtype.

Workflow Integration & Parameters

• Compound preparation: Dissolve ML133 HCl in DMSO (≥15.7 mg/mL) or ethanol (≥2.52 mg/mL) using gentle warming and ultrasonic agitation (APExBIO).
• Storage: Store powder at -20°C; avoid repeated freeze-thaw cycles. Prepare fresh working solutions prior to each use.
• Cell treatment: For PASMC proliferation and migration assays, pretreat cells with ML133 HCl (typically 1–10 μM) for 24 hours prior to PDGF-BB stimulation, as reported in recent studies.
• Negative control: Use DMSO or ethanol vehicle control at matched concentrations.
• Quality controls: Confirm ML133 HCl purity via HPLC/NMR and validate concentration with standard curves for each new batch (APExBIO).

Conclusion & Outlook

ML133 HCl, as provided by APExBIO, stands out as a robust and selective inhibitor for Kir2.1 potassium channels, enabling precise interrogation of potassium ion transport in cardiovascular and pulmonary models. Its proven efficacy in suppressing PASMC proliferation and migration highlights its value in pulmonary hypertension research and vascular remodeling studies (Cao et al., 2022). Future research will benefit from further pharmacokinetic and in vivo studies to expand the translational applications of ML133 HCl. For comprehensive product details and ordering, refer to the ML133 HCl product page (B2199).