Recovery Interstitial PO2 Dynamics Following Contractions in Healthy Skeletal Muscle of Different Oxidative Capacity

Abstract

Listen

Translate article

The recovery of skeletal muscle from repetitive tasks is dependent, in part, on adequate O2 delivery and blood-mitochondrial O2 diffusion. Key steps in this pathway include the microvascular and interstitial space (is) and novel use of specific phosphorescence probes allow measurements of O2 partial pressures (PO2) at those sites near the myocytes. Given the disparate contribution of nitric oxide (NO) between fiber types we sought to resolve how NO impacts PO2is in recovery following rhythmic muscle contractions. PURPOSE: To determine the contribution of NO bioavailability to the temporal profiles of PO2is off-kinetics in two fast-twitch muscles with different oxidative capacities (citrate synthase: peroneal (PER) ~20 vs white gastrocnemius (WG) ~8-11 μmol/min/g). We tested the hypothesis that the more oxidative PER would display faster kinetics while recovering to baseline PO2is levels compared to the WG. In addition, NO synthase inhibition via L-nitroarginine methyl ester (L-NAME) would slow recovery off- kinetics whereas this process would be speeded by increased NO. METHODS: PO2is was determined via phosphorescence quenching (Oxyphor G4) in the exposed rat PER and WG (n=5) during and following electrically stimulated muscle contractions (1 Hz, 8 V, both 3 min) under control (CON), sodium nitroprusside (SNP, NO donor) and L-NAME (n= 3 PER, 5 WG) conditions. RESULTS: PER PO2is was higher than WG for CON at baseline (18.1 ± 1.8 vs 11.3 ± 1.2 mmHg), end contractions (11.5 ± 1.2 vs 5.2 ± 0.9 mmHg), and following recovery (19.6 ± 2.1 vs 10.1 ± 0.9 mmHg; p<0.05 for all). SNP elevated PO2is at all time points in both muscles compared to CON and L-NAME (p<0.05). PO2is recovered to baseline levels in both muscles in CON and L-NAME (p>0.05) but not SNP (p<0.05). Off-kinetics were faster in the PER compared to WG in CON (35 ± 6 vs 76 ± 6 s; p<0.05). L-NAME did not alter PER off-kinetics but prolonged recovery in WG (101 ± 8 s; p<0.05). CONCLUSIONS: Consistent with our hypothesis, PO2is returned to baseline levels faster in the CON PER than WG. This likely reflects greater O2 delivery in PER. However, NO synthase inhibition via L-NAME did not diminish the magnitude nor rate of recovery in PER indicating that the interstitial-mitochondrial pressure head for O2 delivery may be preserved via other pathways in more oxidative muscles in health.