Myocardial Glucose Uptake Is Regulated by Nitric Oxide via Endothelial Nitric Oxide Synthase in Langendorff Mouse Heart

Abstract

Although the role of nitric oxide (NO) in the modulation of vascular tone has been studied and well understood, its potential role in the control of myocardial metabolism is only recently evident. Several lines of evidence indicate that NO regulates myocardial glucose metabolism; however, the details and mechanisms responsible are still unknown. The aim of this study was to further define the role of NO in the control of myocardial glucose metabolism and the nitric oxide synthase (NOS) isoform responsible using transgenic animals lacking endothelial NOS (ecNOS). In the present study, we examined the regulation of myocardial glucose uptake using isometrically contracting Langendorff-perfused hearts from normal mice (C57BL/6J), mice with defects in the expression of ecNOS [ecNOS (-/-)], and its heterozygote [ecNOS (+/-)], and wild-type mice [ecNOS (+/+)] (n=6, respectively). In hearts from normal mice, little myocardial glucose uptake was observed. This myocardial glucose uptake increased significantly in the presence of N(omega)-nitro-L-arginine methyl ester (L-NAME). Similarly, in the hearts from ecNOS (-/-), glucose uptake was much greater than in normal mice, whereas myocardial glucose uptake of ecNOS (+/-) and ecNOS (+/+) mice was not different from normal mice. In addition, myocardial glucose uptake of ecNOS (+/-) and ecNOS (+/+) mice increased significantly in the presence of L-NAME. At a workload of 800 g. beats/min, L-NAME increased glucose uptake from 0.1+/-0.1 to 3+/-0.4 microg/min x mg in ecNOS (+/-) mice and from 0.2+/-0.1 to 2.7+/-0.7 microg/min x mg in ecNOS (+/+) mice. Furthermore, in the hearts from ecNOS (-/-) mice, 8-bromoguanosine 3':5'-cyclic monophosphate (8-Br-cGMP), a cGMP analog or S-nitroso-N-acetylpenicillamine (SNAP), a NO donor essentially shut off glucose uptake, and in hearts from ecNOS (+/-) mice, 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ), an inhibitor of cGMP, increased the glucose uptake significantly. These results indicate clearly that cardiac NO production regulates myocardial glucose uptake via a cGMP-dependent mechanism and strongly suggest that ecNOS plays a pivotal role in this regulation. These findings may be important in the understanding of the pathogenesis of the diseases such as ischemic heart disease, heart failure, diabetes mellitus, hypertension, and hypercholesterolemia, in which NO synthesis is altered and substrate utilization by the heart changes.

Guanylyl cyclase is an ATP sensor coupling nitric oxide signaling to cell metabolism

“…Thus, NO and the associated production of cGMP decrease the transport, availability through glycogenoloysis, and metabolic activation of glucose (9,10). Conversely, cGMP increases the transport and utilization of fatty acids as metabolic substrates, which are associated with a more favorable respiratory quotient (6,14).…”

“…Well described mechanisms control the selection of substrates and routing of their flux through anaerobic and aerobic metabolic pathways, ultimately leading to oxidative phosphorylation and the production of ATP in mitochondria (1,6,(10)(11)(12)(13)(14)39). More recently, the importance of spatially organized intracellular enzymatic networks supporting high-energy phosphoryl transfer in coupling ATP generation in mitochondria on the one hand, and ATP-consuming or -sensing processes on the other, has emerged (1).…”

“…Moreover, in some models of severe hypoxic stress, NO induces complete and reversible metabolic stasis required to survive the insult (19). The importance of NO in defending against ischemia is underscored by its regulation of the transcription factor hypoxia inducible factor 1, a master regulator of cellular homeostasis in the context of oxygen insufficiency (20).Coordination of energy supply and demand is mediated, in part, by NO activation of soluble guanylyl cyclase (sGC) and the associated accumulation of intracellular cGMP concentration ([cGMP] i ) (9,10,12,15,16,18), yet the mechanisms coordinating cGMP-dependent and metabolic signaling, beyond the production of NO, remain undefined. Recently, a novel mechanism was identified by which adenine nucleotides inhibit GCs (21,22) that is analogous to P site inhibition of adenylyl cyclases (23).…”

“…Metabolic stress, such as ischemia, stimulates NO synthases to produce NO from arginine (3). In turn, NO regulates the supply of energy by improving the delivery of substrates and oxygen to deprived tissues (4)(5)(6), regulating the intracellular delivery of metabolic substrates (7)(8)(9)(10), selection of substrates that support metabolism (6,(10)(11)(12)(13)(14), oxidation of metabolic substrates (15), generation of ATP by improving metabolic efficiency (16), and biogenesis of mitochondria (17). Conversely, NO reduces the demand for ATP by decreasing energyconsuming cell functions, for example, by reducing the activity of the contractile apparatus in muscle cells (ref.…”

“…Coordination of energy supply and demand is mediated, in part, by NO activation of soluble guanylyl cyclase (sGC) and the associated accumulation of intracellular cGMP concentration ([cGMP] i ) (9,10,12,15,16,18), yet the mechanisms coordinating cGMP-dependent and metabolic signaling, beyond the production of NO, remain undefined. Recently, a novel mechanism was identified by which adenine nucleotides inhibit GCs (21,22) that is analogous to P site inhibition of adenylyl cyclases (23).…”