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Regulation of amino acid transport in chick embryo heart cells. IV. Site and mechanism of insulin action

1974; Elsevier BV; Volume: 356; Issue: 2 Linguagem: Inglês

10.1016/0005-2736(74)90285-5

1879-2642

Guido Guidotti, R. Franchi‐Gazzola, Gian C. Gazzola, Paolo Ronchi,

Nitric Oxide and Endothelin Effects

The regulation of amino transport by insulin in chick embryo heart cells has been studied. Experiments were designed to identify the system(s) of mediation involved in this regulation and to investigate the mechanisms of the hormone action. Results and conclusions based on the adopted experimental approach include the following: 1. Among the four systems (A, ASC, L, Ly+) found to be operative in cardiac cells for the transport of neutral and basic amino acids (Gazzola, G. C., Franchi-Gazzola, R., Ronchi, P. and Guidotti, G. G. (1973) Biochim. Biophys. Acta 311, 292–301), only the A mediation is responsive to insulin. 2. The hormone enhances the activity of this mediation by increasing the maximal velocity (V) of transport (without substantial changes in Km) even under conditions of inhibited protein synthesis. 3. The rate of degradation of protein components of the A mediation (as estimated by measurements of transport activity under conditions of inhibited protein synthesis) is decreased when cells are incubated in the presence of insulin. The hormone does not affect this rate for systems ASC, L and Ly+. 4. Cells previously incubated in a medium containing cycloheximide (phase of inhibited translation) subsequently exhibit a net increase of transport activity (A mediation) when transferred into a medium containing actinomycin D (phase of inhibited transcription). The presence of insulin during pre-incubation in cycloheximide has no effect on the subsequent rate of change in transport activity; when added to the second phase, the hormone definitely enchances transport activity. 5. These observations have been interpreted to indicate that insulin modulates the activity of the A transport system by acting at two different sites; at the cell membrane by protecting specific transport proteins against degradation and at a post-transcriptional level by increasing the rate of synthesis of these transport proteins.