Insulin-stimulated glucose transport inhibits Ca2+ influx and contraction in vascular smooth muscle
Kahn, A.M.; Lichtenberg, R.A.; Allen, J.C.; Seidel, C.L.; Song, T.
Circulation 92(6): 1597-1603
1995
ISSN/ISBN: 0009-7322 PMID: 7664446 Document Number: 448816
Background: Insulin attenuates serotonin-induced Ca-2+ influx, the intracellular Ca-2+ transient, and contraction of cultured vascular smooth muscle cells from dog femoral artery. These studies were designed to test whether insulin-induced glucose transport was an early event leading to the inhibitory effects of insulin on Ca-2+ influx, intracellular Ca-2+ concentration, and contraction in these cells. Methods and Results: Insulin 1 nmol/L stimulated the 30-minute uptake of (3H)2-deoxyglucose in these cells via a phloridzin-inhibitable mechanism. Contraction of individual cells was measured by photomicroscopy, intracellular Ca-2+ concentration was monitored by measuring fura 2 fluorescence by use of Ca-2+-sensitive excitation wavelengths, and Ca-2+ influx was estimated by the rate of Mn-2+ quenching of intracellular fura 2 fluorescence when excited at a Ca-2+-insensitive wavelength. In the presence of 5 mmol/L glucose, preincubation of cells for 30 minutes with 1 nmol/L insulin inhibited 10-5 mol/L serotonin-induced contraction of individual cells by 62% (P lt .01) and decreased the serotonin-stimulated component of Mn-2+ influx by 78% (P lt .05). Removing glucose from the preincubation medium or adding 1 mmol/L phloridzin completely eliminated these effects of insulin. Insulin lowered the serotonin-induced intracellular Ca-2+ peak by 37% (P lt .05), and phloridzin blocked this effect of insulin. When glucose uptake was increased to the insulin-stimulated level by preincubation of the cells for 30 minutes with 25 mmol/L glucose in the absence of insulin, serotonin failed to stimulate Mn-2+ influx, the serotonin-induced Ca-2+ peak was decreased by 46% (P lt .05), serotonin-induced contraction was inhibited by 60% (P lt .01), and addition of insulin did not further inhibit contraction. Conclusions: Since the effects of insulin on serotonin-stimulated Ca-2+ transport, intracellular Ca-2+ concentration, and contraction were dependent on glucose transport and were duplicated when glucose transport was stimulated by high extracellular glucose concentration rather than insulin per se, it is concluded that insulin-stimulated glucose transport is an early event that leads to decreased Ca-2+ influx and contraction in vascular smooth muscle.