Iodothyronine Interactions with the System L1 Amino Acid Exchanger in 3T3-L1 Adipocytes

Figure 5

Phenylalanine efflux from 3T3-L1 adipocytes. (a) Time course of phenylalanine efflux showing the trans stimulatory effect of leucine. The cumulative release of [³H]phenylalanine from cells preloaded with the tracer was measured in the presence or absence of extracellular leucine over the time period indicated. Values are shown ± SEM for 6–18 measurements (smaller error bars are obscured by symbols). $C_0$ represents the cellular radioactivity at the start of the experiment and $C_t$ is that at time $t$, as calculated from the sum of cumulative radiotracer appearance in the medium and residual cellular radioactivity. The rate constant for efflux was taken as the gradient of the line of best fit. (b) Effects of external amino acids on rate constant for phenylalanine efflux. Bars indicate rate constants calculated as described in (a) and error bars represent SEM for gradient of the line of best fit. *$P<.05$, **$P<.01$; value significantly different from basal value.

(a)

(b)