Acetylcholine microiontophoresis augmented the conduction of hyperpolarization along hamster feed arteries, increasing the length constant to 1.9 mm compared to 1.2 mm with electrical stimuli (P<0.05).
Does acetylcholine augment the conduction of hyperpolarization along hamster feed arteries compared to purely electrical stimuli?
Acetylcholine augments the conduction of hyperpolarization along the vessel wall of hamster feed arteries beyond what is explained by passive electrical decay.
Effect estimate: 60% further
Absolute Event Rate: 1.9% vs 1.2%
p-value: p=< 0.05
The conduction of vasodilation along resistance vessels has been presumed to reflect the electrotonic spread of hyperpolarization from cell to cell along the vessel wall through gap junction channels. However, the vasomotor response to acetylcholine (ACh) encompasses greater distances than can be explained by passive decay. To investigate the underlying mechanism for this behavior, we tested the hypothesis that ACh augments the conduction of hyperpolarization. Feed arteries (n = 23; diameter, 58 +/- 4 microm; segment length, 2-8 mm) were isolated from the hamster retractor muscle, cannulated at each end, and pressurized to 75 mmHg (at 37 degrees C). Vessels were impaled with one or two dye-containing microelectrodes simultaneously (separation distance, 50 microm to 3.5 mm). Membrane potential (E(m)) (rest, approximately -30 mV) and electrical responses were similar between endothelium and smooth muscle, as predicted for robust myoendothelial coupling. Current injection (-0.8 nA, 1.5 s) evoked hyperpolarization (-10 +/- 1 mV; membrane time constant, 240 ms) that conducted along the vessel with a length constant (lambda) = 1.2 +/- 0.1 mm; spontaneous E(m) oscillations (approximately 1 Hz) decayed with lambda = 1.2 + 0.1 mm. In contrast, ACh microiontophoresis (500 nA, 500 ms, 1 microm tip) evoked hyperpolarization (-14 +/- 2 mV) that conducted with lambda = 1.9 +/- 0.1 mm, 60% further (P < 0.05) than responses evoked by purely electrical stimuli. These findings indicate that ACh augments the conduction of hyperpolarization along the vessel wall.
Emerson et al. (Mon,) reported a other. Acetylcholine (ACh) microiontophoresis vs. Current injection (purely electrical stimuli) was evaluated on Length constant (lambda) of hyperpolarization conduction (60% further, p=< 0.05). Acetylcholine microiontophoresis augmented the conduction of hyperpolarization along hamster feed arteries, increasing the length constant to 1.9 mm compared to 1.2 mm with electrical stimuli (P<0.05).