Inhibition of myocardial glucose uptake by cGMP

Abstract

Guanosine 3′,5′-cyclic monophosphate (cGMP), a second messenger of nitric oxide (NO), regulates myocardial contractility. It is not known whether this effect is accompanied by a change in heart metabolism. We report here the effects of 8-bromoguanosine 3′,5′-cyclic monophosphate (8-BrcGMP), a cGMP analog, on regulatory steps of glucose metabolism in isolated working rat hearts perfused with glucose as the substrate. When glucose uptake was stimulated by increasing the workload, addition of the cGMP analog totally suppressed this stimulation and accelerated net glycogen breakdown. 8-BrcGMP did not affect pyruvate dehydrogenase activity but activated acetyl-CoA carboxylase, the enzyme that produces malonyl-CoA, an inhibitor of long-chain fatty acid oxidation. To test whether glucose metabolism could also be affected by altering the intracellular concentration of cGMP, we perfused hearts with N G-nitro-l-arginine methyl ester (l-NAME), an inhibitor of NO synthase, or with S-nitroso- N-acetylpenicillamine (SNAP), a NO donor. Perfusion withl-NAME decreased cGMP and increased glucose uptake by 30%, whereas perfusion with SNAP resulted in opposite effects. None of these conditions affected adenosine 3′,5′-cyclic monophosphate concentration. Limitation of glucose uptake by SNAP or 8-BrcGMP decreased heart work, and this was reversed by adding alternative oxidizable substrates (pyruvate, β-hydroxybutyrate) together with glucose. Therefore, increased NO production decreases myocardial glucose utilization and limits heart work. This effect is mediated by cGMP, which is thus endowed with both physiological and metabolic properties.

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).…”

“…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).…”

Glucose for the Heart

“…Addition of cGMP analogues or NO donors to perfused hearts decreases glucose uptake and glycolytic flux. 101 Thus, cGMP probably downregulates glucose uptake during ischemia, as the addition of NO synthase inhibitors to ischemic heart stimulates glucose metabolism and improves the resistance against ischemia. 83 …”