The purpose of this study was to develop a new rodent model that is capable of delineating the importance of mechanical loading on myosin heavy chain (MHC) isoform expression of the plantar and dorsi flexor muscles of the ankle. The essential components of this system include 1) stimulating electrodes that are chronically implanted into a muscle, allowing for the control of the activation pattern of the target muscle(s); 2) a training apparatus that translates the moment of the ankle into a linear force; and 3) a computer-controlled Cambridge 310 ergometer. The isovelocity profile of the ergometer ensured that the medial gastrocnemius (MG) produced forces that were > 90% of maximal isometric force (Po), and the eccentric contractions of the tibialis anterior (TA) were typically 120% of Po. Both the concentric and eccentric training programs produced statistically significant increases in the muscle mass of the MG (approximately 15%) and TA (approximately 7%) as well as a decrease in myofibrillar adenosinetriphosphatase activity. Both the white and red regions of the MG and TA exhibited significant increases in the relative content of the type IIa MHC and concomitant decreases in type IIb MHC expression. Although the red regions of the MG and red TA contained approximately 10% type I MHC, the training programs did not affect this isoform. It appears that when a fast-twitch muscle is stimulated at a high frequency (100 Hz) and required to contract either concentrically or eccentrically under high loading conditions, the expression of the type IIa MHC isoform will be upregulated, whereas that of the type IIb MHC will be concomitantly downregulated.

Adenosine Triphosphatases↗

PubMed1992

Ion-exchange chromatography (IC) in the determination of serum transition metals and its clinical application.

The reproducibility of ion-exchange chromatography (IC) (Dionex Bio-LC) in measuring the serum transition metals Cu and Zn was found to be fairly good (CV = +/- 2.1% and +/- 2.7% within runs, and +/- 2.5% and +/- 4.3% among runs for Cu and Zn, respectively). For clinical application, sera from 20 normal volunteers and 20 patients with cancers of the digestive tract (10 early and 10 late stage cases) were analyzed. The means of serum Cu (15.54 +/- 0.31 mumol/L) and serum Zn (14.84 +/- 0.31 mumol/L) in normal volunteers were very close to the values previously determined by atomic absorption spectrophotometry in our laboratory. In the group of late stage cancer patients, the means of serum Cu (24.18 +/- 0.63 mumol/L) and the Cu/Zn ratio (1.97 +/- 0.07) were significantly elevated (P < 0.01), while serum Zn (13.01 +/- 0.61 mumol/L) was remarkably decreased (P < 0.05). There were no significant changes of serum Cu, Zn and Cu/Zn ratio in early stage cancer patients. It is concluded that the IC method is rapid, accurate, sensitive, relatively simple and could be useful in diagnosing late stage cancers of the digestive tract.

Adult↗

PubMed1991