| dc.description.abstract | Regulation of cytosolic calcium (Ca2+) levels in muscle is vital to the health and function of muscle due to its involvement in various signaling pathways and cell functions. Sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) pumps are found on the membrane of the sarcoplasmic reticulum (SR) and function to actively transport Ca2+ from the cytosol into the SR. Previous work has shown that in the face of heat stress (HS), a model for oxidative stress, heat shock protein 70 (Hsp70) expression is induced to protect the cytosolic domain and function of SERCA. Having previously found that, sarcolipin (SLN) and phospholamban (PLN), which regulate SERCA in the transmembrane (TM) region of the pump, can also preserve SERCA function using both in-vitro and ex-vivo HS models we wanted to assess if they can be stress-induced proteins like Hsp70. The purpose of this project was to assess the sex differences in basal protein expression of Hsp70, SLN, and PLN and the effect of in-vivo heat stress on SERCA function, total protein nitrosylation status, and gene and protein time-course expression pattern of the three proteins in male and female rat soleus and white gastrocnemius (WG) muscles. The heat stress protocol involved submerging the lower limbs of the animals either in a 37ºC (control) or 42-42.5ºC (HS) water bath to either maintain core temperature at 37ºC (control) or between 41-41.5ºC for 30 mins and were either allowed no recovery or were allowed to recover for 24 or 48 hours. Analysis of basal expression found that i) Hsp70 gene expression was higher in both muscles in the females, but its protein levels were higher in the male soleus, ii) SLN gene expression was also higher in both muscles in the females, but no sex differences were observed in the protein levels, and iii) PLN protein expression was higher in the male soleus. In-vivo heat stress i) did not affect SR Ca2+ uptake in the solei of both sexes whereas, in the WG, SR Ca2+ uptake was increased after 24 hours in both sexes ii) did not have an effect on the protein nitrosylation status in the soleus of male and female rats and on WG of female rats, iii) induced both gene and protein expression of Hsp70 in the soleus and WG of both male and female rats, iv) induced protein expression of SLN in the male soleus but only gene expression of Sln in the male WG whereas the same effects were not observed in the females and v) did not induce Pln gene expression in either muscle, but did induce PLN protein expression only in the WG of males. The findings from this study show that even with a relatively mild acute stress model like the one used here, both SLN and PLN were upregulated at least in one muscle of males, indicating that these proteins may also function as stress-induced proteins. | en |
