Miyuki Kato

Effects of low-intensity prolonged exercise on PGC-1 mRNA expression in rat epitrochlearis muscle

We previously reported that the peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) mRNA in rat epitrochlearis muscle was increased after swimming exercise training. In the present study, we demonstrated further that PGC-1 mRNA expression in the epitrochlearis muscle of 4-5-week-old male Sprague-Dawley rats was increased after a 6-h acute bout of low-intensity swimming exercise. With this increase, the expression level was approximately 8-fold of control and immersion group rats that stayed for 6-h in warm water, maintained at the identical temperature of the swimming barrel (35 degrees C) (p<0.01). Second, PGC-1 mRNA expression in the muscle was found to have increased 6-h after 30 10-s tetani contractions were induced by in vitro electrical stimulation. Finally, PGC-1 mRNA expression in the muscle incubated for 18-h with 0.5mM 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR: a 5 AMP-activated protein kinase (AMPK) activator) was elevated to approximately 3-fold of the control muscle (n=6, p<0.001). AMPK activity in epitrochlearis muscle after the swimming was also found to be elevated to approximately 4-fold of the pre-exercise value (p<0.001). These results may suggest that an acute bout of low-intensity prolonged swimming exercise directly enhances the PGC-1 mRNA expression in the activated muscle during exercise, possibly through, at least in part, an AMPK-related mechanism.

Effect of YM-126414 on glucose uptake and redistribution of glucose transporter isotype 4 in muscle cells

We discovered a novel compound, YM-126414 [1,3, 3-trimethyl-2-(2-phenylaminovinyl)-3H-indolium perchlorate], which stimulates glucose uptake in skeletal muscle cells in vitro. This compound increased the rate of consumption of glucose by C2C12 mouse myoblast cells in a dose-dependent manner (EC(50)=10 nM). To investigate the mechanism of this stimulation, we determined the redistribution of insulin-regulatable glucose transporter isotype 4 (Glut4). When fully differentiated C2C12 cells stably expressing myc-tagged Glut4 protein were treated with YM-126414, redistribution was dramatically increased in a dose-dependent manner (EC(50)=21 nM). These results indicate that YM-126414 is a novel glucose uptake stimulator for muscle cells by causing up-regulation of Glut4 redistribution in differentiated muscle cells. Our findings for the in vitro effects of YM-126414 suggest a direction for the development of new drugs for the treatment of type 2 diabetes.

Glucose uptake stimulator YM‐138552 activates gene expression and translocation of glucose transporter isotype 4

In this study, we examined the effect of YM‐138552 on the glucose uptake, gene expression, and transport activities of the insulin‐regulatable glucose transporter isotype 4 (Glut4) in skeletal muscle cells. YM‐138552 stimulated medium glucose consumption in a dose‐dependent manner (EC50 = 0.07 μM) in myoblast muscle C2C12 cells under differentiation conditions with 2% horse serum supplement. The stimulatory effect of glucose consumption was verified by radiolabeled 2‐DG uptake assay. The compound showed dose‐dependent stimulation of 2‐DG uptake in G8 myoblast muscle cells up to a 1 μM concentration (EC50 = 0.19 μM). To investigate the mechanism of glucose uptake stimulation by YM‐138552, the mRNA level of Glut4 was determined using real‐time quantitative RT‐PCR. The Glut4 mRNA level expressed in C2C12 cells treated with YM‐138552 increased up to at least 24 h (227% vs. control), after which it gradually decreased to the initial level at 36 h. In addition, we established that C2C12 cells stably expressed the myc‐tagged Glut4 protein (C2C12‐Glut4myc) and measured the Glut4 translocation activity. The Glut4 translocation activity was stimulated by treatment of YM‐138552 without insulin in a dose‐dependent manner (EC50 = 0.62 μM), and no insulin effect (100 nM) was observed. This suggests that YM‐138552 has an insulin‐like effect. These results suggest that the stimulation of glucose uptake by YM‐138552 in muscle cells was partly due to upregulation of the Glut4 gene expression and its translocation activation. Our findings on the in vitro effects of YM‐138552 glucose uptake stimulation through the Glut4 transporter may suggest a direction for the development of new drugs for the treatment of NIDDM. Drug Dev. Res. 51:43–48, 2000.