MRI of Potassium and Sodium Enables Comprehensive Analysis of Ion Perturbations in Skeletal Muscle Tissue After Eccentric Exercise

Abstract

Objectives: The aims were to investigate if potassium ( 39 K) magnetic resonance imaging (MRI) can be used to analyze changes in the apparent tissue potassium concentration (aTPC) in calf muscle tissue after eccentric exercise and in delayed-onset muscle soreness, and to compare these to corresponding changes in the apparent tissue sodium concentration (aTSC) measured with sodium ( 23 Na) MRI. Materials and Methods: Fourteen healthy subjects (7 female, 7 male; 25.0 ± 2.8 years) underwent 39 K and 23 Na MRI at a 7 T MR system, as well as 1 H MRI at a 3 T MR system. Magnetic resonance imaging data and blood samples were collected at baseline (t0), directly after performing eccentric exercise (t1) and 48 hours after exercise (t2). Self-reported muscle soreness was evaluated using a 10-cm visual analog scale for pain (0, no pain; 10, worst pain) at t0, t1, and t2. Quantification of aTPC/aTSC was performed after correcting the measured 39 K/ 23 Na signal intensities for partial volume and relaxation effects using 5 external reference phantoms. Edema volume and 1 H T 2 relaxation times were determined based on the 1 H MRI data. Participants were divided according to their increase in creatine kinase (CK) level into high (CK t2 ≥ 10•CK t0 ) and low CK (CK t2 < 10•CK t0 ) subjects.Results: Blood serum CK and edema volume were significantly increased 48 hours after exercise compared with baseline ( P < 0.001). Six participants showed a high increase in blood serum CK level at t2 relative to baseline, whereas 8 participants had only a low to moderate increase in blood serum CK. All participants reported increased muscle soreness both at rest and when climbing stairs at t1 (0.4 ± 0.7; 1.4 ± 1.2) and t2 (1.6 ± 1.4; 4.8 ± 1.9) compared with baseline (0 ± 0; 0 ± 0). Moreover, aTSC was increased at t1 in exercised muscles of all participants (increase by 57% ± 24% in high CK, 73% ± 33% in low CK subjects). Forty-eight hours after training, subjects with high increase in blood serum CK still showed highly increased aTSC (increase by 79% ± 57% compared with t0). In contrast, aTPC at t2 was elevated in exercised muscles of low CK subjects (increase by 19% ± 11% compared with t0), in which aTSC had returned to baseline or below. Overall, aTSC and aTPC showed inverse evolution, with changes in aTSC being approximately twice as high as in aTPC. Conclusions: Our results showed that 39 K MRI is able to detect changes in muscular potassium concentrations caused by eccentric exercise. In combination with 23 Na MRI, this enables a more holistic analysis of tissue ion concentration changes.

Water and Electrolyte Content in Salt-Dependent HYpertension in the SKIn (WHYSKI): Effect of Surgical Cure of Primary Aldosteronism

“…Hence, it still needs further validation in human studies in vivo using a gold reference method as the direct measurement of skin Na + , along with K + and water with atomic absorption spectrophotometry after ashing [ 21 ]. Furthermore, parallel 1 H-MRI studies are necessary to measure tissue water content [ 12 ], and although recently implemented to measure muscle K + content [ 22 ], MRI has not provided information on the skin K + content in hypertensive patients. Thus, it remains to be settled if, and to what extent, tissue Na + measurement with 23 Na-MRI are affected by concomitant changes of water and other electrolytes.…”

A century of exercise physiology: effects of muscle contraction and exercise on skeletal muscle Na+,K+-ATPase, Na+ and K+ ions, and on plasma K+ concentration—historical developments

“…More recently, muscle 23 Na was measured in several muscles in 3 women and 3 men, including m. triceps surae , peroneal and superficial flexor muscles, medial and lateral m. gastrocnemius and m. soleus , with Na + c increased from a mean resting value of 34.0 (31.9–34.9) to 37.3 (35.3–38.9) mmol·kg ww −1 after incremental cycling (Hammon et al 2015 ) . Recent MRI studies using a 7 T magnet have used muscle 23 Na, 39 K and 1 H measurements to calculate [K + ] and [Na + ] (Chang et al 2010 ; Gast et al 2022a , b ; Höger et al 2022 ). In 7 females and 7 males, in medial and lateral m. gastrocnemius , m. soleus and m. tibialis anterior , [K + ] ranged between 96 and 100 mM and [Na + ] between 16 and 19 mM (Gast et al 2022b ), and after 5 min eccentric contractions, [K + ] had not changed whilst [Na + ] had increased to ~ 26 to 28 mM (Gast et al 2022a ), with Na + c also elevated after eccentric contractions in medial m. gastrocnemius and m. soleus (Höger et al 2022 ).…”

“…Recent MRI studies using a 7 T magnet have used muscle 23 Na, 39 K and 1 H measurements to calculate [K + ] and [Na + ] (Chang et al 2010 ; Gast et al 2022a , b ; Höger et al 2022 ). In 7 females and 7 males, in medial and lateral m. gastrocnemius , m. soleus and m. tibialis anterior , [K + ] ranged between 96 and 100 mM and [Na + ] between 16 and 19 mM (Gast et al 2022b ), and after 5 min eccentric contractions, [K + ] had not changed whilst [Na + ] had increased to ~ 26 to 28 mM (Gast et al 2022a ), with Na + c also elevated after eccentric contractions in medial m. gastrocnemius and m. soleus (Höger et al 2022 ). In summary, recent MRI measurements have reported increased muscle [Na + ] and decreased [K + ] with exercise, especially when fatigue is involved, which are qualitatively consistent with the previous studies using muscle biopsies (Table 7 ).…”

Magnetic resonance imaging techniques for the quantitative analysis of skeletal muscle: State of the art

“…Using dedicated ultra-high field MRI systems (B 0 ​≥ ​7 ​T), also other ions such as potassium or chloride can be investigated using 39 K or 35 Cl MRI to provide a more comprehensive analysis of the tissue ion homeostasis [ 119 , 120 ]. However, so far, 35 Cl and 39 K MRI of skeletal muscle tissue have only been performed in small feasibility studies [ [121] , [122] , [123] ].…”