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Effects of elevation of phosphocreatine on force and metabolism in rabbit aorta
Insights
Loading rabbit aorta rings with creatine increased intracellular creatine and phosphocreatine by 300%. However, this did not alter ATP levels or contractile function, suggesting limited impact on energy metabolism.
Area of Science:
- Biochemistry
- Physiology
- Cellular Metabolism
Background:
- Creatine plays a crucial role in cellular energy buffering.
- Phosphocreatine (PCr) serves as a readily available phosphate reservoir for ATP regeneration.
- Understanding creatine uptake and its metabolic fate in vascular tissue is important for assessing its physiological impact.
Purpose of the Study:
- To investigate the effects of exogenous creatine loading on intracellular creatine and phosphocreatine levels in rabbit thoracic aorta.
- To determine the impact of creatine loading on ATP content, PCr-to-Cr ratio, and contractile function.
- To assess the influence of creatine loading on energy metabolism and substrate utilization during rest, contraction, and hypoxic conditions.
Main Methods:
- Rabbit thoracic aorta rings were incubated with 40 mM creatine for 4 hours.
- Intracellular creatine (Cr) and phosphocreatine (PCr) content were measured.
- ATP content and PCr-to-Cr ratios were analyzed.
- Contractile responses to norepinephrine were assessed.
- ATP production rates were calculated from mitochondrial and glycolytic metabolism.
- PCr depletion and lactate efflux were measured under various metabolic stress conditions (hypoxia, zero-glucose).
Main Results:
- Intracellular Cr and PCr content increased by 300% in 4 hours, while ATP content and PCr-to-Cr ratio remained constant.
- Exogenous Cr was taken up and metabolized to PCr, which was available for tissue metabolism.
- Creatine-loaded rings showed no difference in norepinephrine-induced contraction rate or amplitude compared to controls.
- ATP production rates were similar in creatine-loaded and control rings during rest and contraction.
- Creatine-loaded rings exhibited a threefold larger decrease in PCr content but no change in PCr/Cr ratio during force development or under hypoxia/zero-glucose conditions.
- Loaded rings showed reduced lactate efflux during hypoxia in normal glucose medium.
Conclusions:
- Exogenous creatine is efficiently taken up and converted to phosphocreatine in rabbit aorta, but does not significantly alter basal ATP levels or contractile performance.
- While creatine loading increases the total phosphocreatine pool, its utilization during sustained contraction or hypoxia is enhanced, leading to greater PCr depletion without affecting the PCr/Cr ratio.
- Creatine loading may influence substrate utilization pathways, as indicated by reduced lactate efflux under hypoxic conditions.
Abstract:
Rings of rabbit thoracic aorta were incubated in 40 mM creatine; both intracellular free creatine (Cr) and phosphocreatine (PCr) content increased 300% in 4 h, whereas tissue ATP content and PCr-to-Cr ratio remained constant. Exogenous Cr was taken up and metabolized by creatine kinase; the newly formed PCr was available for tissue metabolism. Compared with control tissue, muscle rings with markedly increased Cr and PCr content showed no difference in either the rate of contraction with norepinephrine or the amplitude of contraction. ATP production rates, computed from mitochondrial and glycolytic metabolism during rest and during maintained contractions, were similar for creatine-loaded and control rings. Under conditions where muscle was developing force, creatine-loaded rings showed a threefold larger decrease in PCr content than untreated rings but no difference in the decrease in PCr/Cr. A similar pattern of PCr depletion was seen when creatine-loaded or untreated NE-contracted muscle was exposed to hypoxia plus zero-glucose medium. In addition, loaded rings showed smaller rates of efflux of lactate than did unloaded rings when exposed to hypoxia in normal glucose medium.