Plasma ATP concentration and venous oxygen content in the forearm during dynamic handgrip exercise

Abstract

Background: It has been proposed that adenosine triphosphate (ATP) released from red blood cells (RBCs) may contribute to the tight coupling between blood flow and oxygen demand in contracting skeletal muscle. To determine whether ATP may contribute to the vasodilatory response to exercise in the forearm, we measured arterialised and venous plasma ATP concentration and venous oxygen content in 10 healthy young males at rest, and at 30 and 180 seconds during dynamic handgrip exercise at 45% of maximum voluntary contraction (MVC).

Results: Venous plasma ATP concentration was elevated above rest after 30 seconds of exercise (P < 0.05), and remained at this higher level 180 seconds into exercise (P < 0.05 versus rest). The increase in ATP was mirrored by a decrease in venous oxygen content. While there was no significant relationship between ATP concentration and venous oxygen content at 30 seconds of exercise, they were moderately and inversely correlated at 180 seconds of exercise (r = -0.651, P = 0.021). Arterial ATP concentration remained unchanged throughout exercise, resulting in an increase in the venous-arterial ATP difference.

Conclusions: Collectively these results indicate that ATP in the plasma originated from the muscle microcirculation, and are consistent with the notion that deoxygenation of the blood perfusing the muscle acts as a stimulus for ATP release. That ATP concentration was elevated just 30 seconds after the onset of exercise also suggests that ATP may be a contributing factor to the blood flow response in the transition from rest to steady state exercise.

Figure 1

Study design. ATP_v - venous blood sample for ATP assay, ATP_a - arterialised blood sample for ATP assay, O2_v - venous blood sample for measurement of blood variables, O2_a - arterialised blood sample for measurement of blood variables. Heart rate was measured continuously throughout the session.

Figure 2

ATP concentration (Panel A) and venous oxygen content (Ct_vO₂; Panel B) at rest, and 30 and 180 seconds into dynamic handgrip exercise at 45% MVC. Dashed lines are the individual responses; n = 9 for ATP concentration and n = 10 for venous oxygen content; bolded solid line is the mean response (n = 9 for ATP concentration and n = 10 for Ct_vO₂).