Vasoactive Responses of Mesenteric Arteries

Vasoconstrictor reactivity and changes in vessel wall [Ca²⁺]_i to the α₁-adrenergic agonist phenylephrine (PE; Sigma-Aldrich) was assessed by superfusion (5 ml/min at 37°C) of cumulative concentrations of PE (10⁻⁸ to 10⁻⁵ M) in isolated rat mesenteric arteries. To assess vasodilatory responses, arteries were first preconstricted (∼30–50%) with the thromboxane A₂ analog, U-46619 (Cayman Chemical), before the superfusion of cumulative concentrations of the muscarinic receptor agonist, ACh (10⁻⁹ to 10⁻⁵ M; Sigma-Aldrich) or arachidonic acid (AA; 10⁻⁸ to 10⁻⁵ M; Cayman Chemical). To determine the contribution of ASIC1a to PE vasoconstrictor and ACh vasodilatory responses, arteries were pretreated (lumen and bath) with the specific ASIC1a antagonist, psalmotoxin 1 (PcTX1, 20 nM; Phoenix Peptides). To assess vasodilation to the ASIC1 agonist, α/β-MitTx, isolated mesenteric arteries were luminally perfused at a rate of 50 µl/min with a bolus of α/β-MitTx (200 nM). In separate experiments, vasodilatory responses were determined in arteries following pretreatment with the NO synthase inhibitor, Nω-nitro-L-arginine (L-NNA; 100 μM; Sigma-Aldrich); cyclooxygenase inhibitor, indomethacin (10 μM; Sigma-Aldrich); or the IK_Ca channel antagonist, Tram-34 (1 μM; Tocris Bioscience); and the SK_Ca antagonist, Apamin (100 μM; Tocris Bioscience) as described previously (Naik and Walker, 2018 (link)).