title: Plasticity of microvascular oxygenation control in rat fast-twitch muscle: effects of experimental creatine depletion.
abstract: Aging, heart failure and diabetes each compromise the matching of O2 delivery (Q˙O2)-to-metabolic requirements (O2 uptake, V˙O2) in skeletal muscle such that the O2 pressure driving blood-myocyte O2 flux (microvascular PO2, PmvO2) is reduced and contractile function impaired. In contrast, β-guanidinopropionic acid (β-GPA) treatment improves muscle contractile function, primarily in fast-twitch muscle (Moerland and Kushmerick, 1994). We tested the hypothesis that β-GPA (2% wt/BW in rat chow, 8 weeks; n=14) would improve Q˙O2-to-V˙O2 matching (elevated PmvO2) during contractions (4.5V @ 1Hz) in mixed (MG) and white (WG) portions of the gastrocnemius, both predominantly fast-twitch). Compared with control (CON), during contractions PmvO2 fell less following β-GPA (MG -54%, WG -26%, P<0.05), elevating steady-state PmvO2 (CON, MG: 10±2, WG: 9±1; β-GPA, MG 16±2, WG 18±2 mmHg, P<0.05). This reflected an increased Q˙O2/V˙O2 ratio due primarily to a reduced V˙O2 in β-GPA muscles. It is likely that this adaptation helps facilitate the β-GPA-induced enhancement of contractile function in fast-twitch muscles.
authors.affiliation: Department of Kinesiology, University of Texas at Arlington, Arlington, TX 76019, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: McDonough
authors.forename: Danielle J
authors.initials: DJ
authors.lastname: Padilla
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Kano
authors.forename: Timothy I
authors.initials: TI
authors.lastname: Musch
authors.forename: David C
authors.initials: DC
authors.lastname: Poole
authors.forename: Brad J
authors.initials: BJ
authors.lastname: Behnke
mesh_terms: D000818:Animals; D003401:Creatine / Q000187:drug effects / Q000378:metabolism*; D006146:Guanidines / Q000494:pharmacology*; D008833:Microcirculation / Q000187:drug effects*; D009119:Muscle Contraction / Q000187:drug effects*; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects*; D018482:Muscle, Skeletal / Q000502:physiology; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption; D010725:Phosphocreatine / Q000187:drug effects / Q000378:metabolism*; D011422:Propionates / Q000494:pharmacology*; D051381:Rats
chemical_list: D006146:Guanidines; D011422:Propionates; D010725:Phosphocreatine; D003401:Creatine; D010100:Oxygen; C005775:guanidinopropionic acid