Responses to raised extracellular potassium, but not ACh, are capsaicin sensitive.

<p>The effect of capsaicin on responses to raised extracellular potassium (A) or ACh (B) in rat isolated mesenteric small arteries at 90 mmHg. All experiments were carried out presence of L-NAME (100 µM and indomethacin (1 µM). Each point represents the mean ± s.e.mean. ***<i>P</i><0.001 capsaicin versus control; <i>n</i> = 4–5.</p

ACh causes hyperpolarization in pressurized small arteries, while raising extracellular potassium does not.

<p>Summary data showing the change in membrane potential in smooth muscle cells from <i>n</i> different animals in response to ACh (1 µM) and raised extracellular potassium (+5 mM) at (A) 30 mmHg and (C) 90 mmHg. Following the successful impalement of a cell, responses to ACh or potassium were recorded in random order. Bars represent mean ± s.e.mean (<i>n</i> = 3–6). Representative trace recording (B) of the change in membrane potential of a rat mesenteric small artery held at 30 mmHg and exposed to ACh (1 µM) followed by raised extracellular potassium (+5 mM). The large deflections at the start and end of the trace recording reflect cell impalement and removal of the microelectrode, respectively.</p

ACh produces a larger vasodilator response than raising extracellular potassium in myogenically-active mesenteric small arteries.

<p>Vasodilator responses to (A) ACh and (B) raised extracellular potassium in rat isolated mesenteric small arteries pressurised to 60 mmHg or 90 mmHg (in the presence of L-NAME and indomethacin). Following the development of stable myogenic tone, cumulative concentration response curves were constructed to ACh or potassium in random order in the same artery from <i>n</i> different animals. Each point represents the mean ± s.e.mean (n = 6–9).</p

Vasodilator responses to raised extracellular potassium correlate with the degree of myogenic tone.

<p>The relationship between the level of myogenic tone (in the presence of L-NAME (100 µM) and indomethacin (1 µM)) and the R_max for ACh (<i>n</i> = 31) or raised extracellular potassium (<i>n</i> = 20) in rat isolated mesenteric arteries pressurised to 90 mmHg. Each point represents one experiment. The slope of the line fitted to the potassium data was significantly different from zero (<i>P</i><0.05) with an r² = 0.2387. The slope of the line fitted to the ACh data was not significantly different from zero.</p