ABAP-Derived Peroxyl Radicals Remodel Intestinal Smooth Muscle Contractility via Potassium Channels, Calcium Influx and Eicosanoid Signaling: Pharmacological and Molecular Docking Strategies

ABAP-derived peroxyl radicals modulate rabbit ileum longitudinal smooth muscle through coordinated actions on ion channels, calcium handling, eicosanoid pathways, and kinase signaling. In isolated preparations, ABAP (20 mM) produced rapid relaxation (basal tone ~0.15–0.20 g), reduced contraction frequency (~9–10 to 6–7 cpm), and paradoxically increased amplitude by ~40–50%. These effects persisted following hexamethonium (100 μM), atropine (1 μM), and lidocaine (100 μM), indicating independence from nicotinic, muscarinic, and nerve-dependent mechanisms. Potassium channel blockade with 4-aminopyridine, tetraethylammonium, or clotrimazole increased tone and abbreviated the silent period from ~110–120 s to 35–84 s, implicating KCa and other K⁺ conductances. Recovery of rhythmicity required L-type Ca²⁺ influx and intracellular store release, as verapamil (1 μM) and caffeine abolished phasic contractions. Lipoxygenase inhibition with NDGA prolonged silence to 354 s and depressed activity, whereas quinacrine shortened silence to 17 s, implicating lipoxygenase-derived eicosanoids in contractile modulation under oxidative stress. Orthovanadate (1 mM) elevated tone and prolonged silence (~200 s) when combined with ABAP, suggesting interplay with tyrosine-phosphorylation-dependent mechanisms. Molecular docking revealed AAPH bound M3 muscarinic receptor, EGFR tyrosine kinase, COX-2, and 5-LOX with affinities of −5.0 to −6.7 kcal·mol⁻¹, forming stabilizing hydrogen bonds and electrostatic contacts. These findings support a model wherein peroxyl radicals directly modulate intestinal motility through K⁺ channel activation, Ca²⁺ signaling, eicosanoid biosynthesis, and kinase pathways, with potential direct interactions at M3 receptors, EGFR, COX-2, and 5-LOX.