Ionomycin, but not physiologic doses of epinephrine, stimulates skeletal muscle Interleukin-6 mRNA expression and protein release

Abstract

It has been hypothesized that epinephrine may stimulate interleukin (IL)-6 gene expression in skeletal muscle. The aim of the present study was to examine the effect of epinephrine on IL-6 gene expression within, and protein release from, skeletal muscle. We hypothesized that physiologic epinephrine would neither result in an increase in IL-6 mRNA nor protein release from skeletal muscle. Soleus muscle was excised from 4-week-old anesthetized Sprague Dawley rats and incubated in a Krebs buffer with the addition of either saline (CON), epinephrine, at concentrations of 1,000 nmol/L (EPI 1,000), 100 nmol/L (EPI 100), or 10 nmol/L (EPI 10), or the calcium ionophore, ionomycin (IONO), a positive control. After a 1-hour incubation, muscle was collected and extracted for RNA, reverse transcribed, and IL-6 gene expression was determined by real-time polymerase chain reaction (PCR). An aliquot of incubation medium was also collected and analyzed for IL-6 protein by enzyme-linked immunosorbent (ELISA). EPI 1,000 and IONO increased (P < .05) IL-6 mRNA, whereas EPI 100 and EPI 10 were without effect. IL-6 protein release from skeletal muscle was increased in IONO (P < .05), but not in CON or EPI at any concentration. These data demonstrate that while pharmacologic concentrations of epinephrine activate IL-6 mRNA, supraphysiologic and high-physiologic doses appear to have little, if any, effect on IL-6 gene transcription in skeletal muscle. In addition, ionomycin can stimulate IL-6 gene expression and protein release after only 1 hour of exposure.