Electrical activation of endothelium evokes vasodilation and hyperpolarization along hamster feed arteries

Abstract

Endothelial cells are considered electrically unexcitable. However, endothelium-dependent vasodilators (e.g., acetylcholine) often evoke hyperpolarization. We hypothesized that electrical stimulation of endothelial cells could evoke hyperpolarization and vasodilation. Feed artery segments (resting diameter: 63 ± 1 μm; length 3–4 mm) of the hamster retractor muscle were isolated and pressurized to 75 mmHg, and focal stimulation was performed via microelectrodes positioned across one end of the vessel. Stimulation at 16 Hz (30–50 V, 1-ms pulses, 5 s) evoked constriction (−20 ± 2 μm) that spread along the entire vessel via perivascular sympathetic nerves, as shown by inhibition with tetrodotoxin, ω-conotoxin, or phentolamine. In contrast, stimulation with direct current (30 V, 5 s) evoked vasodilation (16 ± 2 μm) and hyperpolarization (11 ± 1 mV) of endothelial and smooth muscle cells that conducted along the entire vessel. Conducted responses were insensitive to preceding treatments, atropine, or N ω-nitro-l-arginine, yet were abolished by endothelial cell damage (with air). Injection of negative current (≤1.6 nA) into a single endothelial cell reproduced vasodilator responses along the entire vessel. We conclude that, independent of ligand-receptor interactions, endothelial cell hyperpolarization evokes vasodilation that is readily conducted along the vessel wall. Moreover, electrical events originating within a single endothelial cell can drive the relaxation of smooth muscle cells throughout the entire vessel.