Nitric Oxide Stimulates Skeletal Muscle Glucose Transport Through a Calcium/Contraction– and Phosphatidylinositol-3-Kinase–Independent Pathway

Abstract

Recently published data have provided evidence that nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) are signaling intermediates in the pathway through which muscle contraction stimulates glucose transport. As exercise promotes both NO production and calcium flux, we examined the relationships between NO-stimulated glucose uptake and calcium-, contraction-, and phosphatidylinositol-3-kinase (PI-3-K)-mediated glucose transport in the isolated incubated rat epitrochlearis muscle preparation. The NO donor sodium nitroprusside (SNP; 10 mmol/1) and dibutyryl cGMP (100 umol/1) accelerated epitrochlearis glucose transport four-to fivefold above basal levels (P < 0.001) in a manner similar to in vitro contractile activity and the calcium releasing agent iV-(6-aminohexyl)-5-chloro-l-naphthalenesulfonamide (W7; 100 umol/1). In the case of SNP, this effect could be completely attributed to an increase in cell surface GLUT4. The effect of SNP on glucose transport was not inhibitable by either wortmannin (1.5 umol/1) or dantrolene (12.5 umol/1). Similarly, neither calcium nor contraction stimulation of glucose transport was affected by the NO synthase inhibitors A^-monomethyl-L-arginine (L-NMMA; 100 umol/1) or 7-nitroindazole (1 mmol/1). Furthermore, whereas SNP raised epitrochlearis cGMP levels tenfold (P < 0.001), neither in vitro contractile activity nor W7 significantly elevated cGMP. These results indicate that NO/cGMP can markedly stimulate skeletal muscle glucose transport by increasing GLUT4 levels at the cell surface by a mechanism that does not depend on activation of PI-3-K. In addition, since calcium/contraction-stimulated glucose transport is not blocked by NO synthase inhibition and did not elevate cGMP, NO/cGMP may be part of a novel pathway that is distinct from both the insulin-and contraction-activated mechanisms.

Effects of the nitric oxide donor, sodium nitroprusside, on resting leg glucose uptake in patients with type 2 diabetes

“…The fact that SNP is able to increase glucose uptake in both cell culture and isolated muscle preparations suggests that NO has a direct action on glucose transport via SLC2A4 translocation, in addition to increasing glucose delivery via effects on blood flow. In support of this hypothesis, SNP was recently shown to increase SLC2A4 translocation and glucose uptake in rat anterior and posterior left ventricular papillary muscles [29] and skeletal muscle [16]. While NO is an important metabolite of SNP [30], it is also possible that SNP exerts its actions via ferrocyanide [27].…”

“…SNP increases glucose transport in a number of cell culture models including human peripheral blood mononuclear cells [24], 3T3-L1 adipocytes [25], L929 fibroblasts [26], isolated rat cardiomyocytes [27] and human vascular smooth muscle cells [28]. SNP also increases glucose transport in isolated rat skeletal muscle preparations [13,[16][17][18][19]. The fact that SNP is able to increase glucose uptake in both cell culture and isolated muscle preparations suggests that NO has a direct action on glucose transport via SLC2A4 translocation, in addition to increasing glucose delivery via effects on blood flow.…”

“…While the evidence for a role of NO in glucose uptake is overwhelming, the specific involvement of NO in contraction-mediated glucose uptake is not without controversy. Two NOS inhibition studies in rats have failed to show any effect on contraction-stimulated glucose uptake [16,17], although both measured glucose uptake after completion of exercise or electrical stimulation, while the human studies displaying positive NOS inhibition results measured glucose uptake during exercise [20,21].…”

“…Electrical stimulation, eliciting muscle contraction causes release of NO [15]. Animal studies have demonstrated that NO donor drugs such as sodium nitroprusside (SNP) increase glucose transport in skeletal muscle [13,[16][17][18][19]. SNP also increases SLC2A4 translocation in isolated rat skeletal muscle preparations [16].…”

“…Animal studies have demonstrated that NO donor drugs such as sodium nitroprusside (SNP) increase glucose transport in skeletal muscle [13,[16][17][18][19]. SNP also increases SLC2A4 translocation in isolated rat skeletal muscle preparations [16]. Of clinical relevance is the observation that NOS inhibition during cycle exercise reduced leg glucose uptake by 48% in young, healthy humans independently of effects on leg blood flow or plasma insulin levels [20].…”