Abstract
Angiotensin-converting enzymes 1 (ACE1) and 2 (ACE2) are key enzymes of the renin-angiotensin system, which act antagonistically to regulate the levels of angiotensin II (Ang II) and Ang-(1-7). Considerable data show that ACE1 acts on normal skeletal muscle functions and architecture. However, little is known about ACE1 levels in muscles with different fiber compositions. Furthermore, ACE2 levels in skeletal muscle are not known. Therefore, the purpose of this study was to characterize protein expression and ACE1 and ACE2 activities in the soleus and plantaris muscles. Eight-week-old female Wistar rats (N = 8) were killed by decapitation and the muscle tissues harvested for biochemical and molecular analyses. ACE1 and ACE2 activities were investigated by a fluorometric method using Abz-FRK(Dnp)P-OH and Mca-YVADAPK(Dnp)-OH fluorogenic substrates, respectively. ACE1 and ACE2 protein expression was analyzed by Western blot. ACE2 was expressed in the skeletal muscle of rats. There was no difference between the soleus (type I) and plantaris (type II) muscles in terms of ACE2 activity (17.35 ± 1.7 vs 15.09 ± 0.8 uF·min(-1)·mg(-1), respectively) and protein expression. ACE1 activity was higher in the plantaris muscle than in the soleus (71.5 ± 3.9 vs 57.9 ± 1.1 uF·min(-1)·mg(-1), respectively). Moreover, a comparative dose-response curve of protein expression was established in the soleus and plantaris muscles, which indicated higher ACE1 levels in the plantaris muscle. The present findings showed similar ACE2 levels in the soleus and plantaris muscles that might result in a similar Ang II response; however, lower ACE1 levels could attenuate Ang II production and reduce bradykinin degradation in the soleus muscle compared to the plantaris. These effects should enhance the aerobic capacity necessary for oxidative muscle activity.
Highlights
The renin-angiotensin system (RAS) has been identified as an important target in the regulation of blood pressure as well as fluid and electrolyte balance [1,2]
A comparative dose-response curve for Angiotensin-converting enzymes 1 (ACE1) protein expression was confirmed by protein load
The present study identified the activity and protein expression of ACE1 and ACE2 in skeletal muscles with a predominance of different types of fiber
Summary
The renin-angiotensin system (RAS) has been identified as an important target in the regulation of blood pressure as well as fluid and electrolyte balance [1,2]. Recent data have demonstrated that the skeletal muscle RAS reflects a combination of in situ synthesis of RAS components and uptake of these constituents from the circulation [3]; the activity of ACE1 in the human skeletal muscle does not correlate with that of serum ACE1 [4]. Skeletal muscle ACE1 activity has been demonstrated in cell membrane fractions and cultured myoblasts [5]. RAS components are present throughout the skeletal muscle microcirculation, including endothelial cells, vascular smooth muscle cells, and other vessel-associated cells [6]. ACE insertion/deletion polymorphism is clear evidence that different ACE1 levels may induce prevalence of type I or II fibers associated with skeletal muscle phenotype and performance [9,10]
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