KCa3.1 encodes the intermediate-conductance calcium-activated potassium channel KCa3.1, a regulator of membrane potential and calcium-dependent signalling in cardiovascular and immune cells. Increasing evidence indicates that KCa3.1 is a shared driver of vascular remodelling, inflammation, fibrosis, and electrical instability across multiple cardiovascular diseases. In ischaemic heart disease (IHD), KCa3.1 is upregulated in endothelial cells, vascular smooth muscle cells, macrophages, and T lymphocytes, where it promotes smooth muscle proliferation, neointimal formation, and chronic vascular inflammation. Genetic deletion or pharmacological blockade of KCa3.1 reduces atherosclerotic plaque burden and restenosis in animal models. In atrial fibrillation (AF), KCa3.1 contributes to electrical remodelling by shortening atrial action potential duration and to structural remodelling by driving fibroblast activation and collagen deposition. KCa3.1 also regulates macrophage polarisation and pro-inflammatory cytokine release in atrial tissue, linking immune activation to arrhythmogenic substrate formation. Inhibition of KCa3.1 prolongs atrial refractoriness, attenuates atrial fibrosis, and reduces AF inducibility in multiple preclinical models. Emerging data in valvular heart disease suggest that KCa3.1 is upregulated in valvular interstitial cells and regions of active calcification, where it supports myofibroblast differentiation, osteogenic signalling, and inflammatory crosstalk, implicating the channel in fibrocalcific valve degeneration. Collectively, these findings position KCa3.1 as a central molecular integrator of electrical, fibrotic, and inflammatory pathways in cardiovascular disease. The availability of selective KCa3.1 inhibitors with established human safety profiles supports the feasibility of therapeutic translation. Targeting KCa3.1 may enable disease-modifying strategies that extend beyond symptom control to suppress maladaptive cardiovascular remodelling.

Background/Objectives: Idiopathic pulmonary fibrosis (IPF) and other progressive fibrotic interstitial lung diseases (F-ILD) are characterised by progressive loss of lung function, worsening symptoms, and poor prognosis. Current antifibrotic therapies slow disease progression but do not arrest or reverse fibrosis and are frequently associated with adverse effects. Senicapoc, a selective KCa3.1 channel inhibitor, has shown antifibrotic effects in preclinical models, human lung myofibroblasts, and ex vivo human lung tissue. This study aims to determine whether senicapoc reduces the rate of decline in forced vital capacity (FVC) over 26 weeks, compared with placebo, in patients with IPF or other progressive F-ILD, while also characterising safety and tolerability. Methods: This is an investigator-initiated, prospective, randomised, double-blind, placebo-controlled, multicentre phase II trial. Adults with IPF or other F-ILD with documented progression despite optimised antifibrotic management according to standard care and individual tolerability will be randomised 1:1 to receive senicapoc 30 mg once daily or a matching placebo for 26 weeks in addition to standard care. The primary outcome is the rate of decline in FVC over 26 weeks. Secondary outcomes include changes in diffusion capacity, 6 min walk distance, dyspnoea, health-related quality of life, adverse events, and senicapoc plasma concentrations, with mortality and exacerbations assessed as exploratory outcomes. The planned sample size is 140 participants. The primary analysis will be conducted in the intention-to-treat population using a linear mixed-effects model for repeated measurements. Results: No results are available, as this article describes the study protocol. Conclusions: This study will provide proof of concept for the efficacy, safety, and tolerability of senicapoc in progressive fibrotic interstitial lung disease. If successful, it will support further clinical development of KCa3.1 inhibition as a novel antifibrotic strategy.