Figure 1. Experimental protocols.

After catheterization of the brachial artery and subject instrumentation, the change in forearm vascular conductance (ΔFVC) in response to ACh or sodium nitroprusside (SNP) was assessed during rest, handgrip exercise at 5% maximal voluntary contraction (MVC) or a high flow control vasodilator condition. Protocol 1: the vasodilatory response to ACh was assessed at rest, during 5% MVC exercise and during a high flow control SNP infusion, before and after infusion of barium chloride (BaCl₂) to block inwardly rectifying potassium (K_IR) channels. Protocol 2: the vasodilatory response to SNP was assessed at rest, during 5% MVC exercise and during a high flow control ACh infusion. In a subset of subjects, the vasodilatory response to ACh was assessed before and after pharmacological activation of K_IR channels via infusion of potassium chloride (KCl).