Small and intermediate Ca²⁺-sensitive K⁺ channels do not play a role in vascular conductance during resting blood flow in the anaesthetised pig

Abstract

Flow-induced dilation in resistance arteries is mediated by endothelium-dependent hyperpolarisation via small and intermediate conducting Ca²⁺ sensitive K⁺ channels. The aim of the current study was to assess the effect of blocking both channels, using the toxins apamin and charybdotoxin, on flow-induced dilation in a conduit artery and vascular conductance. Experiments were carried out on the iliac and its vascular bed in anaesthetised pigs (n = 4). Flow-induced dilation and vascular conductance (∆F/∆P) were assessed before and after administration of toxins intra-arterially (i.a.) at 50 µg kg⁻¹. Iliac diameter increased from baseline to 2.39 ± 0.4 mm before and 2.09 ± 0.46 mm after toxin administration, which was not significantly different (P = 0.63, Student’s paired t test). Control conductance was 1.49 ± 0.27 ml min⁻¹ mmHg⁻¹ (P < 0.00001, ANOVA), and 1.53 ± 0.18 ml min⁻¹ mmHg⁻¹ (P < 0.00001, ANOVA) in the presence of the toxins which was not significantly different (P = 0.93 homogeneity of regression analysis). There was a small but significant increase in mean arterial pressure after the toxins were administered, from 74 ± 5 to 80 ± 9 mmHg (P = 0.03, Student’s paired t test); but all other measured parameters were not significantly affected. Small- and intermediate-conducting Ca²⁺-sensitive K⁺ channels are not involved in flow-mediated dilation in conduit arteries and do not play a role in resistance vessel diameter maintenance at resting blood flow.