Venous plasma potassium is not associated with maintenance of the exercise pressor reflex in humans

Increases in the concentration of interstitial potassium concentration during exercise may play a role in the modulation of the cardiovascular response to exercise. However, it is not known if changes in potassium correlate with indexes of muscle reflex engagement. Eight healthy subjects performed dynamic [rhythmic handgrip (RHG)] and static handgrip (SHG) exercise at 40% of maximal voluntary contraction. Forearm circulatory arrest was performed to assess the metaboreceptor component of the exercise pressor reflex. Mean arterial pressure (MAP) and muscle sympathetic nerve activity (MSNA) were measured during each exercise paradigm. Venous plasma potassium concentrations ([K⁺]_V) were measured and used as a surrogate marker for interstitial potassium. [K⁺]_V were measured at baseline and at 1-min intervals during dynamic handgrip. During SHG, [K⁺]_V were measured at baseline, 30 and 90 s of exercise, and twice during forearm circulatory arrest. Mean [K⁺]_V was 3.6 mmol/l at rest before both paradigms. During RHG, [K⁺]_V rose by ∼1.0 mmol/l by min 2 and remained constant throughout the rest of handgrip. During SHG, [K⁺]_V rose significantly at 30 s and rose an additional ∼1.0 mmol/l by peak exercise. MAP and MSNA rose during both exercise paradigms. During posthandgrip circulatory arrest (PHG-CA), MSNA and blood pressure remained above baseline. [K⁺]_V and MSNA did not correlate during either exercise paradigm. Moreover, during PHG-CA, there was clear dissociation of MSNA from [K⁺]_V. These data suggest that potassium does not play a direct role in the maintenance of the exercise pressor reflex.