Insulin-Induced Glucose Transporter (GLUT1 and GLUT4) Translocation in Cardiac Muscle Tissue Is Mimicked by Bradykinin

Abstract

The effect of bradykinin on glucose transporter translocation in isolated rat heart was compared with the effect of insulin. Hearts from male obese (fa/fa) Zucker rats were perfused under normoxic conditions and constant pressure in a classic Langendorff preparation with 12 mmol/l glucose as substrate, and a set of functional parameters was measured 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 glucose transport in this model. After 15 min of perfusion with insulin or bradykinin, subcellular membrane fractions of the heart were prepared, and distribution of glucose transporter protein (GLUT1 and GLUT4) in fractions enriched with surface membranes (transverse tubules [TTs] and sarcolemmal membranes [PMs]) and with low-density microsomal membranes (LDMs) were determined by immunoblotting with the respective antibodies. Both glucose transporter isoforms were translocated after stimulation with insulin (increased transporter protein content in the PM+TT-enriched fraction with a concomitant decrease in the LDM-enriched fraction) and, to a smaller extent, also with bradykinin. These data suggest that in hearts of insulin-resistant obese (fa/fa) Zucker rats, bradykinin interacts with or facilitates the translocation process of both GLUT1 and GLUT4.