K+ as a vasodilator in resting human muscle: implications for exercise hyperaemia

Area of Science:

• Physiology
• Cardiovascular Research

Background:

• Potassium (K(+)) released from contracting skeletal muscle is traditionally viewed as a vasodilator.
• This concept is largely based on studies using non-physiological K(+) concentrations.

Purpose of the Study:

• To investigate the precise role of K(+) in regulating blood flow.
• To determine if physiological K(+) levels induce vasodilation in resting skeletal muscle.

Main Methods:

• Leg blood flow (LBF) and arterio-venous O(2) difference were measured in 13 subjects.
• Graded infusions of K(+) were administered into the femoral artery.
• The effect of Ba(2+), a Kir2.1 channel inhibitor, on K(+)-induced vasodilation was assessed.

Main Results:

• Physiological K(+) infusions significantly increased LBF and decreased the arterio-venous O(2) difference, indicating vasodilation.
• The vasodilatory effect of K(+) was completely blocked by Ba(2+) inhibition of Kir2.1 channels.
• The combined effect of ATP and K(+) on LBF was additive.

Conclusions:

• Physiological K(+) levels induce vasodilation in resting skeletal muscle via Kir2.1 channels.
• K(+) released during muscle contraction likely contributes to exercise-induced hyperemia.
• However, K(+) alone may only account for a small portion of the overall exercise hyperemic response.