Differential effect of 4-bromocrotonic acid on basal and insulin-stimulated glucose transport in 3t3-l1 adipocytes

Two inhibitors of fatty acid oxidation, 2-bromopalmitic acid (Br-C16) and 4-bromocrotonic acid (Br-C4) were examined for their effect on glucose transport in 3T3-L1 adipocytes. While Br-C16 was without effect, Br-C4 augmented basal but inhibited insulin-stimulated 2-deoxyglucose (2-DG) uptake in a dose- and time-dependent manner. Neither protein synthesis inhibitors nor L-carnitine had any effect on the action of Br-C4. Also, lactate release from adipocytes was not altered by either Br-C4 or Br-C 16 pretreatment. Whereas the sensitivity (EC50) of insulin to stimulate 2-DG uptake was not changed, the efficacy (maximal response) of insulin was decreased. In addition, glucose transport in response to vanadate, hydrogen peroxide and okadaic acid were all suppressed in Br-C4 pretreated cells. On the contrary, phorbol ester-stimulated glucose transport was not affected. Immunoblot analysis indicated that following Br-C4 pretreatment membrane content of GLUT 1 was increased whereas insulin-induced translocation of GLUT4 was greatly eliminated. In conclusion, these results seem to suggest that Br-C4 has reciprocal effect on basal and insulin-stimulated glucose transport in 3T3-L1 adipocytes. While oxidative status of mitochondria is not involved in the action of Br-C4, translocation process for both GLUT1 and GLUT4 appears to be altered. (Supported by a NSC grant NSC852331-B-010-OI5, R.O.C).