INSULIN-INDUCED GLUCOSE-TRANSPORTER (GLUT1 AND GLUT4) TRANSLOCATION IN CARDIAC-MUSCLE TISSUE IS MIMICKED BY BRADYKININ

The effect of bradykinin on glucose transporter translocation in isola ted rat heart was compared with the effect of insulin, Hearts from mal e obese (fa/fa) Zucker rats were perfused under normoxic conditions an d constant pressure in a classic Langendorff preparation with 12 mmol/ l glucose as substrate, and a set of functional parameters was measure d simultaneously, Bradykinin was administered at a concentration (10(- 11) mmol/l) that did not increase coronary flow. Insulin was used at a concentration (8 x 10(-8) mmol/l) known to maximally stimulate glucos e transport in this model, After 15 min of perfusion with insulin or b radykinin, subcellular membrane fractions of the heart were prepared, and distribution of glucose transporter protein (GLUT1 and GLUT4) in f ractions enriched with surface membranes (transverse tubules [TTs] and sarcolemmal membranes [PMs]) and with low-density microsomal membrane s (LDMs) were determined by immunoblotting with the respective antibod ies, Both glucose transporter isoforms were translocated after stimula tion with insulin (increased transporter protein content in the PM+TT- enriched fraction with a concomitant decrease in the LDM-enriched fi a ction) and, to a smaller extent, also with bradykinin. These data sugg est that in hearts of insulin-resistant obese (fa/fa) Zucker rats, bra dykinin interacts with or facilitates the translocation process of bot h GLUT1 and GLUT4.