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Inhibition of Na + /K + ‐ATPase and K IR channels abolishes hypoxic hyperaemia in resting but not contracting skeletal muscle of humans
Author(s) -
Racine Matthew L.,
Crecelius Anne R.,
Luckasen Gary J.,
Larson Dennis G.,
Dinenno Frank A.
Publication year - 2018
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jp275913
Subject(s) - hyperaemia , hypoxia (environmental) , medicine , endocrinology , vasodilation , nitric oxide , chemistry , skeletal muscle , forearm , blood flow , cardiology , anatomy , oxygen , organic chemistry
Key points Increasing blood flow (hyperaemia) to exercising muscle helps match oxygen delivery and metabolic demand. During exercise in hypoxia, there is a compensatory increase in muscle hyperaemia that maintains oxygen delivery and tissue oxygen consumption. Nitric oxide (NO) and prostaglandins (PGs) contribute to around half of the augmented hyperaemia during hypoxic exercise, although the contributors to the remaining response are unknown. In the present study, inhibiting NO, PGs, Na + /K + ‐ATPase and inwardly rectifying potassium (K IR ) channels did not blunt augmented hyperaemia during hypoxic exercise beyond previous observations with NO/PG block alone. Furthermore, although inhibition of only Na + /K + ‐ATPase and K IR channels abolished hyperaemia during hypoxia at rest, it had no effect on augmented hyperaemia during hypoxic exercise. This is the first study in humans to demonstrate that Na + /K + ‐ATPase and K IR channel activation is required for augmented muscle hyperaemia during hypoxia at rest but not during hypoxic exercise, thus providing new insight into vascular control.Abstract Exercise hyperaemia in hypoxia is augmented relative to the same exercise intensity in normoxia. During moderate‐intensity handgrip exercise, endothelium‐derived nitric oxide (NO) and vasodilating prostaglandins (PGs) contribute to ∼50% of the augmented forearm blood flow (FBF) response to hypoxic exercise (HypEx), although the mechanism(s) underlying the remaining response are unclear. We hypothesized that combined inhibition of NO, PGs, Na + /K + ‐ATPase and inwardly rectifying potassium (K IR ) channels would abolish the augmented hyperaemic response in HypEx. In healthy young adults, FBF responses were measured (Doppler ultrasound) and forearm vascular conductance was calculated during 5 min of rhythmic handgrip exercise at 20% maximum voluntary contraction under regional sympathoadrenal inhibition in normoxia and isocapnic HypEx (O 2 saturation ∼80%). Compared to control, combined inhibition of NO, PGs, Na + /K + ‐ATPase and K IR channels ( l ‐NMMA + ketorolac + ouabain + BaCl 2; Protocol 1; n = 10) blunted the compensatory increase in FBF during HypEx by ∼50% (29 ± 6 mL min −1 vs . 62 ± 8 mL min −1 , respectively, P < 0.05). By contrast, ouabain + BaCl 2 alone (Protocol 2; n = 10) did not affect this augmented hyperaemic response (50 ± 11 mL min −1 vs . 60 ± 13 mL min −1 , respectively, P > 0.05). However, the blocked condition in both protocols abolished the hyperaemic response to hypoxia at rest ( P < 0.05). We conclude that activation of Na + /K + ‐ATPase and K IR channels is involved in the hyperaemic response to hypoxia at rest, although it does not contribute to the augmented exercise hyperaemia during hypoxia in humans.