EMG-Normalised Kinase Activation during Exercise Is Higher in Human Gastrocnemius Compared to Soleus Muscle

In mice, certain proteins show a highly confined expression in specific muscle groups. Also, resting and exercise/contraction-induced phosphorylation responses are higher in rat skeletal muscle with low mitochondrial content compared to muscles with high mitochondrial content, possibly related to differential reactive oxygen species (ROS)-scavenging ability or resting glycogen content. To evaluate these parameters in humans, biopsies from soleus, gastrocnemius and vastus lateralis muscles were taken before and after a 45 min inclined (15%) walking exercise bout at 69% VO2max aimed at simultaneously activating soleus and gastrocnemius in a comparable dynamic work-pattern. Hexokinase II and GLUT4 were 46–59% and 26–38% higher (p<0.05) in soleus compared to the two other muscles. The type I muscle fiber percentage was highest in soleus and lowest in vastus lateralis. No differences were found in protein expression of signalling proteins (AMPK subunits, eEF2, ERK1/2, TBC1D1 and 4), mitochondrial markers (F1 ATPase and COX1) or ROS-handling enzymes (SOD2 and catalase). Gastrocnemius was less active than soleus measured as EMG signal and glycogen use yet gastrocnemius displayed larger increases than soleus in phosphorylation of AMPK Thr172, eEF2 Thr56 and ERK 1/2 Thr202/Tyr204 when normalised to the mean relative EMG-signal. In conclusion, proteins with muscle-group restricted expression in mice do not show this pattern in human lower extremity muscle groups. Nonetheless the phosphorylation-response is greater for a number of kinase signalling pathways in human gastrocnemius than soleus at a given activation-intensity. This may be due to the combined subtle effects of a higher type I muscle fiber content and higher training status in soleus compared to gastrocnemius muscle

North Atlantic surface ocean warming and salinization in response to middle Eocene greenhouse warming

Quantitative reconstructions of hydrological change during ancient greenhouse warming events provide valuable insight into warmer-than-modern hydrological cycles but are limited by paleoclimate proxy uncertainties. We present sea surface temperature (SST) records and seawater oxygen isotope (δ18Osw) estimates for the Middle Eocene Climatic Optimum (MECO), using coupled carbonate clumped isotope (Δ47) and oxygen isotope (δ18Oc) data of well-preserved planktonic foraminifera from the North Atlantic Newfoundland Drifts. These indicate a transient ~3°C warming across the MECO, with absolute temperatures generally in accordance with trace element (Mg/Ca)–based SSTs but lower than biomarker-based SSTs for the same interval. We find a transient ~0.5‰ shift toward higher (δ18Osw), which implies increased salinity in the North Atlantic subtropical gyre and potentially a poleward expansion of its northern boundary in response to greenhouse warming. These observations provide constraints on dynamic ocean response to warming events, which are consistent with theory and model simulations predicting an enhanced hydrological cycle under global warming

Exercise-induced signalling in different human muscle groups.

<p>Relative work-load during exercise-bout evaluated by A) % of maximal EMG and B) glycogen content in human soleus (SOL), lateral gastrocnemius (Gast) and vastus lateralis (VL) before and after inclined walking exercise at ∼70% VO2max. Measured phosphorylations of C) ERK1/2, D) AMPK and E) eEF2 normalised per total protein in SOL, Gast and VL before and after exercise. F) EMG-normalised phosphorylation per total protein in gastroc. vs. SOL. G) Representative blots. §/§§§ p<0.05/0.001 vs. soleus. *** p<0.001 exercise-effect vs. rest within muscle. ††† p<0.001 muscle-effect, n = 10.</p

Relative protein expression quantified from western blots in human soleus, lateral gastrocnemius (Gastroc.) and lateral vastus of the vastus lateralis muscle (VL). SOD2 showed a borderline significant trend (p = 0.07, 1-way ANOVA).

<p>n = 10.</p><p>*/**/***p<0.05/0.01/0.001 vs. soleus.</p

Blood parameters measured as indicated at various time-points during an inclined walking exercise-bout at ∼70% VO2max.

<p>n = 10.</p><p>*/**/***p<0.05/0.01/0.001 vs. corresponding resting value.</p

Overview of experimental protocol for pre-test day and experimental days 1 and 2.

<p>Overview of experimental protocol for pre-test day and experimental days 1 and 2.</p

North Atlantic surface ocean warming and salinization in response to middle Eocene greenhouse warming

Quantitative reconstructions of hydrological change during ancient greenhouse warming events provide valuable insight into warmer-than-modern hydrological cycles but are limited by paleoclimate proxy uncertainties. We present sea surface temperature (SST) records and seawater oxygen isotope (δ18Osw) estimates for the Middle Eocene Climatic Optimum (MECO), using coupled carbonate clumped isotope (Δ47) and oxygen isotope (δ18Oc) data of well-preserved planktonic foraminifera from the North Atlantic Newfoundland Drifts. These indicate a transient ~3°C warming across the MECO, with absolute temperatures generally in accordance with trace element (Mg/Ca)–based SSTs but lower than biomarker-based SSTs for the same interval. We find a transient ~0.5‰ shift toward higher δ18Osw, which implies increased salinity in the North Atlantic subtropical gyre and potentially a poleward expansion of its northern boundary in response to greenhouse warming. These observations provide constraints on dynamic ocean response to warming events, which are consistent with theory and model simulations predicting an enhanced hydrological cycle under global warming

North Atlantic surface ocean warming and salinization in response to middle Eocene greenhouse warming

Quantitative reconstructions of hydrological change during ancient greenhouse warming events provide valuable insight into warmer-than-modern hydrological cycles but are limited by paleoclimate proxy uncertainties. We present sea surface temperature (SST) records and seawater oxygen isotope (δ18Osw) estimates for the Middle Eocene Climatic Optimum (MECO), using coupled carbonate clumped isotope (Δ47) and oxygen isotope (δ18Oc) data of well-preserved planktonic foraminifera from the North Atlantic Newfoundland Drifts. These indicate a transient ~3°C warming across the MECO, with absolute temperatures generally in accordance with trace element (Mg/Ca)–based SSTs but lower than biomarker-based SSTs for the same interval. We find a transient ~0.5 ‰ shift toward higher δ18Osw, which implies increased salinity in the North Atlantic subtropical gyre and potentially a poleward expansion of its northern boundary in response to greenhouse warming. These observations provide constraints on dynamic ocean response to warming events, which are consistent with theory and model simulations predicting an enhanced hydrological cycle under global warming