Uptake of adenosine by dispersed chich embryonic cardiac cells

Adenosine is involved in the regulation of coronary blood flow, but its mechanism of action is not clear. The present investigation is an attempt to understand the mechanism(s) of uptake of adenosine in dispersed chick embryonic cardiac cells and its relationship to the adenosine hypothesis. Adenosine is readily taken up by these cardiac cells, and a small fraction is incorporated into adenine nucleotides, whereas a major fraction is deaminated to inosine. The mechanism of uptake is different in 12- to 15-day-old chick embryos compared to 16- to 22-day-old embryos. The younger embryo heart cells show the incorporation of adenosine into adenine mononucleotides of the incubation medium as well as all the adenine nucleotides of the cells, whereas the older embryo heart cells show incorporation of adenosine only into the adenine nucleotides of the cells. The isolated cells used in the present study do not leak any significant amounts of adenosine kinase and/or nucleotides, and free adenosine was not found in the cells, even with extracellular concentrations as high as 1 mM. The absence of free adenosine in isolated dispersed cells reflects the activities of adenosine kinase and adenosine deaminase and is compatible with the adenosine hypothesis for the regulation of coronary blood flow.