Glucose uptake in the developing chick embryo heart

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Abstract
The kinetics of glucose transport and phosphorylatlon were studied in chick embryo hearts at various stages of development. In 5-day-old hearts, incubated in the presence of glucose at concentrations which did not cause significant accumulation of Intracellular free glucose, i.e., when uptake approximated inward transport, the apparent Km [Michaelis constant] and Vmax [maximum velocity] for the process were very high and compatible with a mechanism of free diffusion. However, the partial limitation of glucose uptake due to its diffusion through the extracellular space renders this conclusion uncertain. At external glucose concentrations greater than 8 m[image], which allowed free glucose to accumulate in the intracellular compartment, glucose phosphorylation approached saturation when the internal glucose concentration was equal to or larger than 1 m [image]. In 10-day-old hearts, the external concentration of glucose at which free sugar began to accumulate Intracellularly was much greater (24-32 m [image]). Below the 32-m [image] concentration, the Inward transport of glucose as measured by its uptake seemed to follow Michaelis-Menten kinetics with an apparent Km of 1.3 x 10 -2 [image] and a transport maximum of about 30 [mu]moles/g wet wt per hr. Insulin appeared to influence Km more than transport maximum.