Chick embryo heart as a tool for studying cell permeability and insulin action

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Abstract
Glucose uptake by chick embryo hearts at various stages of development was measured in aerobic and anaerobic conditions, with or without the addition of insulin. Glucose uptake per gram of tissue decreases as the age of the embryo increases. Increasing the concentration of glucose in the medium causes an increase in uptake by 5-, 7- and 9-day-old hearts; a plateau is reached only with 5-day-old hearts. Anoxia stimulates glucose uptake at all ages studied; insulin has no effect in 5-day-old hearts, but stimulates glucose uptake in hearts 7 days old or older. The results of these experiments suggest the following conclusions: 1) The 5-day-old chick embryo heart is permeable to glucose and, in this preparation, glucose uptake is limited by the rate of intracellular phosphorylation. 2) During the 7th day of embryologic development, coincident with the first production of beta granules in the pancreas of the embryo, an insulin-sensitive "membrane" regulating glucose uptake begins to develop. In 7-day-old and older hearts, glucose transport becomes the rate-limiting factor of glucose uptake. 3) These and other properties of the chick embryo heart make it a convenient tool for the study of permeability and transport phenomena.