Insulin inhibits vascular smooth muscle contraction at a site distal to intracellular Ca2+ concentration

1 Departments of Medicine, The University of Texas Health Science Center and 2 Baylor College of Medicine, Houston, Texas 77030 Several hypertensive states are associated with resistance to insulin-induced glucose disposal and insulin-induced vasodilation. Insulin can inhibit vascular smooth muscle (VSM) contraction at the level of the VSM cell, and resistance to insulin's inhibition of VSM cell contraction may be of pathophysiological importance. To understand the VSM cellular mechanisms by which insulin resistance leads to increased VSM contraction, we sought to determine how insulin inhibits contraction of normal VSM. It has been shown that insulin lowers the contractile agonist-stimulated intracellular Ca 2+ (Ca 2+ i ) transient in VSM cells. In this study, our goal was to see whether insulin inhibits VSM cell contraction at steps distal to Ca 2+ i and, if so, to determine whether the mechanism is dependent on nitric oxide synthase (NOS) and cGMP. Primary cultured VSM cells from canine femoral artery were bathed in a physiological concentration of extracellular Ca 2+ and permeabilized to Ca 2+ with a Ca 2+ ionophore, either ionomycin or A-23187. The resultant increase in Ca 2+ i contracted individual cells, as measured by photomicroscopy. Preincubating cells with 1 nM insulin for 30 min did not affect basal Ca 2+ i or the ionomycin-induced increase in Ca 2+ i , as determined by fura 2 fluorescence measurements, but it did inhibit ionomycin- and A-23187-induced contractions by 47 and 51%, respectively (both P