The effects of hypoventilation on the physiological and biochemical properties of hindlimb muscles

Abstract

The purpose of this study was to determine physiological and biochemical properties of hindlimb muscles after bilateral phrenic nerve denervation (DNV).Male Wistar rats (10 wk) underwent DNV (n=18) by cutting the phrenic nerve at the cervical level under the stereomicroscope or sham surgery (n=18, CON). Analyses were performed 4, 8 and 12 wks after surgery. The myosin heavy chain (MHC) isoform profile and in vitro isometric contractile properties of the soleus (SOL) and extensor digitram longus (EDL) were analyzed.DNV induced changes in SpO2 characteristic of hypoventilation syndromes. After 12 wks, increases in MHC 1 and decreases in MHC 2a (both p<0.05) were observed in the DNV SOL. Increases in MHC 1 (7%), MHC 2a (7%) and MHC 2d (9%) and decreases in MHC 2b (23%) (all p<0.05) were measured in the DNV EDL. After 8 wks and 12 wks of DNV, the peak twitch force of EDL decreased (~30%) and after 12 wks the fatigue index increased (19%) (all p<0.05). However, DNV did not affect the contractile properties of SOL.In conclusion chronically low SpO2 and decreased hindlimb contractile activity induced by DNV resulted in a unique fast‐to‐slow MHC shift in SOL and EDL. This was accompanied by enhanced fatigue resistance and impaired contractile function in the EDL but not the SOL.This work was supported by Grants‐in‐Aid for Scientific Research from the Japanese Ministry of Science and Technology, no 24500628.