α-Aminoisobutyric acid uptake by cultured beating heart cells

Abstract 1. 1. The uptake of the amino acid analog, α-aminoisobutyric acid (AIB) by cultured beating rat heart cells has been investigated, taking advantage of a culture technique enabling to obtain 80–90 % myoblasts. 2. 2. AIB was found to be transported and accumulated within the myoblasts by a process requiring energy, K + and Na + , as evidenced by the marked drop in AIB uptake observed in myoblasts incubated with oligomycin, or in the absence of Na + or K + in the medium. 3. 3. The observed decrease in net AIB uptake brought about by the lack of either Na + or K + in the medium appears, however, to be related more to drastic changes in ionic gradients than to a modulation of the Na + -K + pump activity, as the myoblasts were very insensitive to ouabain. 4. 4. Glycolysis is likely to be of considerable importance for optimal AIB accumulation by the myoblasts. Thus, iodoacetate markedly inhibited this process; glucose completely overcame the inhibitory effect of oligomycin on net AIB uptake, an action of glucose that could be prevented by further addition of 2-deoxyglucose. 5. 5. When added alone to the incubation medium, insulin failed to alter AIB uptake. However, under conditions in which the energy supply was limited ( e.g. cells treated with oligomycin) and AIB accumulation consequently decreased, the hormone brought the uptake of the amino acid back towards the normal level provided glucose (not pyruvate) was present in the medium. This suggests that insulin acts on the amino acid concentrative process mainly via its well-substantiated stimulatory effect on the transmembrane transport of glucose.