Inhibition by insulin of cellular autophagy in proximal tubular cells of rat kidney

Abstract

Adult male Sprague-Dawley rats were injected intraperitoneally with 5 U insulin/kg body wt (45 animals). As determined by quantitative electron microscopy, the volume fraction and the numerical density of autophagic vacuoles (AV) in proximal tubular cells decreased within 10 min by 46 and 26%, respectively. A partial recovery of the AV volume fraction was observed 20 and 30 min after the injection contrary to our previous findings with liver (J. Cell Biol. 78: 152-167, 1978). In an additional experiment (12 animals) it was shown that an insulin dose of 0.5 U but not of 0.05 U/kg body wt reduced the AV volume fraction to an extent similar to that of 5 U. To eliminate possible secondary effects, Ringer solution containing 0.8 microM insulin was dropped intravitally for 15 min to one pole of the decapsulated kidney and Ringer solution without additions to the other pole (8 animals). After intravital fixation, the AV volume fraction and numerical density in proximal tubular cells was found to be reduced under the influence of insulin by 22 and 36%, respectively. This data shows that insulin inhibits the process of cellular autophagy in proximal tubular cells of the kidney.