TY - JOUR
T1 - Insulin antagonism of catecholamine stimulation of fatty acid transport in the adipocyte. Studies on its mechanism of action
AU - Abumrad, N. A.
AU - Harmon, C. M.
AU - Barnela, U. S.
AU - Whitesell, R. R.
PY - 1988
Y1 - 1988
N2 - Insulin at physiological concentrations can suppress catecholamine activation of the membrane transport of long chain fatty acids in the adipocyte. We have previously shown that the stimulatory effect of catecholamines was mediated by a β-receptor interaction and cAMP (Abumrad, N. A., Park, C. R., and Whitesell, R. R. (1986) J. Biol. Chem. 261, 13082-13086). In this study we have investigated the mechanism of insulin action to antagonize transport activation. Fatty acid transport was stimulated using different cAMP derivatives with varying susceptibilities to hydrolysis by the cAMP-degrading enzyme phosphodiesterase. Insulin was effective in antagonizing the effect of cAMP analogs which were good substrates for the phosphodiesterase and failed to suppress the effect of those which were poorly hydrolyzed by the enzyme. Addition of increasing concentrations (1-100 μM) of the phosphodiesterase inhibitor methylisobutylxanthine (MIX) to norepinephrine (0.1 μg/ml) gradually abolished insulin's antagonism. Insulin was completely ineffective in inhibiting stimulation by norepinephrine and 20 μM methylisobutylxanthine. Also consistent with involvement of cAMP lowering in insulin action was the finding that adenosine removal greatly diminished insulin's responsiveness. Treatment of cells with adenosine deaminase (1 unit/ml) enhanced the effect of norepinephrine by about 30%. A 10-fold higher range of insulin concentrations was then required to produce inhibition of fatty acid transport. The effect of adenosine removal was reversed by addition of phenylisopropyladenosine (500 nM), which is resistant to hydrolysis by the deaminase. Finally, exposure of insulin-treated cells (1 nM for 5 min) to dinitrophenol (1 mM for 5 min) reversed insulin action, consistent with reports of reversal of insulin's activation of the phosphodiesterase. In conclusion, our studies support the involvement of cAMP lowering in insulin's antagonism of fatty acid transport stimulation in the adipocyte.
AB - Insulin at physiological concentrations can suppress catecholamine activation of the membrane transport of long chain fatty acids in the adipocyte. We have previously shown that the stimulatory effect of catecholamines was mediated by a β-receptor interaction and cAMP (Abumrad, N. A., Park, C. R., and Whitesell, R. R. (1986) J. Biol. Chem. 261, 13082-13086). In this study we have investigated the mechanism of insulin action to antagonize transport activation. Fatty acid transport was stimulated using different cAMP derivatives with varying susceptibilities to hydrolysis by the cAMP-degrading enzyme phosphodiesterase. Insulin was effective in antagonizing the effect of cAMP analogs which were good substrates for the phosphodiesterase and failed to suppress the effect of those which were poorly hydrolyzed by the enzyme. Addition of increasing concentrations (1-100 μM) of the phosphodiesterase inhibitor methylisobutylxanthine (MIX) to norepinephrine (0.1 μg/ml) gradually abolished insulin's antagonism. Insulin was completely ineffective in inhibiting stimulation by norepinephrine and 20 μM methylisobutylxanthine. Also consistent with involvement of cAMP lowering in insulin action was the finding that adenosine removal greatly diminished insulin's responsiveness. Treatment of cells with adenosine deaminase (1 unit/ml) enhanced the effect of norepinephrine by about 30%. A 10-fold higher range of insulin concentrations was then required to produce inhibition of fatty acid transport. The effect of adenosine removal was reversed by addition of phenylisopropyladenosine (500 nM), which is resistant to hydrolysis by the deaminase. Finally, exposure of insulin-treated cells (1 nM for 5 min) to dinitrophenol (1 mM for 5 min) reversed insulin action, consistent with reports of reversal of insulin's activation of the phosphodiesterase. In conclusion, our studies support the involvement of cAMP lowering in insulin's antagonism of fatty acid transport stimulation in the adipocyte.
UR - http://www.scopus.com/inward/record.url?scp=0023742968&partnerID=8YFLogxK
M3 - Article
C2 - 2459120
AN - SCOPUS:0023742968
SN - 0021-9258
VL - 263
SP - 14678
EP - 14683
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 29
ER -