Title: Acute and moderate-term creatine monohydrate
supplementation does not affect creatine transporter mRNA or protein content in either young or elderly humans.
Researchers: Tarnopolsky M, Parise G, Fu MH, Brose A, Parshad A, Speer O, Wallimann T.
Institution: Department of Medicine (Neurology and Rehabilitation), McMaster University, Hamilton, ON, Canada.
Source: Molecular and Cellular Biochemistry 2003 Feb;244(1-2):159-66
Summary: Animal studies have shown that supra-physiological creatine monohydrate
supplementation for 3 months reduced skeletal muscle creatine transporter (CRT) content. The doses of Creatine (1-2 g/kg/day) used in these studies were between 5 and 10 times those usually used in human studies, and it is unclear whether a down-regulation of CRT would occur in humans at the recommended doses of 0.1-0.2 g/kg/day.
Methods: CRT, and citrate synthase (CS) protein content were measured using
Western blotting before and after 2 months of Creatine supplementation and weight training in young men using 0.125 g/kg/day. CRT and CS were also measured before and after 4 months of Creatine supplementation and weight training in elderly (> 65 years) men and women using 0.075 g/kg/day. Finally, CRT mRNA was measured using competitive RT-PCR before and after 8-9 days of Creatine loading in young men and women using 0.18 g/kg/day.
Results: Total creatine content was significantly elevated after the Creatine supplementation period as compared to placebo in each of the studies. Neither Creatine supplementation, nor exercise training resulted in measurable alterations in CRT protein content and acute Creatine loading did not alter CRT mRNA. There were no gender differences in CRT mRNA or total creatine content in the young subjects and no gender differences in total creatine content or CRT protein content in the elderly subjects. Weight training in young men did not increase CS protein content, however, in the elderly there was a significant increase in CS protein content after exercise training.
Conclusion: These results demonstrated that Creatine monohydrate supplementation during weight training resulted in increases in skeletal muscle total creatine without reductions in Creatine Transporter protein and acute Creatine loading did not decrease Creatine Transporter mRNA content.