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Our results demonstrate that CIT supplementation has no effect on whole-body protein synthesis or liver protein synthesis in malnourished older subjects. However, CIT supplementation was associated with a higher systemic AA availability. In the subgroup of women, CIT supplementation increased LM and ASMM, and decreased FM.

Protein energy malnutrition in the elderly causes preferential loss of muscle mass which is associated with poor functional states. Leucine and citrulline are able to stimulate muscle protein synthesis in aged rats but no study has been undertaken to evaluate their effect on muscle function. Sprague-Dawley male rats aged 23 months were used in the experiment. Part of them were subjected to a dietary restriction for 12 weeks and then assigned to four groups: a group was euthanized (restricted group), and the others were refed for 1 week with either a leucine-, a citrulline-supplemented diet, or a standard diet. The other rats were fed ad libitum. Muscle mass and motor activity significantly increased during the refeeding with either leucine or citrulline (respectively, +51 and +37% for muscle mass, P < 0.05). The improvement of muscle mass and of motor activity induced by leucine and citrulline was highly associated with that of maximal tetanic isometric force (r = 0.769, P < 0.0001; r = 0.389, P < 0.05, respectively) but only leucine improved maximal tetanic isometric force (+101%, P < 0.05). In conclusion, this is the first study to demonstrate the ability of two amino acids (leucine and citrulline) to modulate muscle function.

. Pore loop-mutated rat KIR6.1 and KIR6.2 suppress KATP current in rat cardiomyocytes. Am J Physiol Heart Circ Physiol 287: H850 -H859, 2004. First published March 25, 2004 10.1152/ajpheart.00054.2004.-Cardiomyocytes express mRNA for all major subunits of ATP-sensitive potassium (KATP) channels: KIR6.1, KIR6.2, SUR1A, SUR2A, and SUR2B. It has remained controversial as to whether KIR6.1 may associate with KIR6.2 to form the tetrameric pore of KATP channels in cardiomyocytes. To explore this possibility, cultured rat cardiomyocytes were examined for an inhibition of K ATP current by overexpression of pore loop-mutated (inactive) KIR6.x. Bicistronic plasmids were constructed encoding loop-mutated (AFA or SFG for GFG) rat KIR6.x followed by EGFP. In ventricular myocytes, the overexpression of KIR6.1SFG-pIRES2-EGFP or KIR6.2AFA-pIRES2-EGFP DNA caused, after 72 h, a major decrease of K ATP current density of 85.8% and 82.7%, respectively (P Ͻ 0.01), relative to EGFP controls (59 Ϯ 9 pA/pF). In atrial myocytes, overexpression of these poremutated KIR6.x by 6.0-fold and 10.6-fold, as assessed by quantitative immunohistochemistry, caused a decrease of KATP current density of 73.7% and 58.5%, respectively (P Ͻ 0.01). Expression of wild-type rat KIR6.2 increased the ventricular and atrial K ATP current density by 58.3% and 42.9%, respectively (P Ͻ 0.01), relative to corresponding EGFP controls, indicating a reserve of SUR to accommodate increased KIR6.x trafficking to the sarcolemma. The results favor the view that KIR6.1 may associate with KIR6.2 to form heterotetrameric pores of native K ATP channels in cardiomyocytes.

Exercise induced a short-term energy deficit. However, modifications in the hormonal regulation of food intake in response to short-term heat or heat and exercise exposure seem to be minor and did not induce changes in energy intake. This trial was registered at clinicaltrials.gov as NCT02157233.

Zinc at micromolar concentrations hyperpolarizes rat pancreatic ␤-cells and brain nerve terminals by activating ATP-sensitive potassium channels (K ATP ). The molecular determinants of this effect were analyzed using insulinoma cell lines and cells transfected with either wild type or mutated K ATP subunits. Zinc activated K ATP in cells coexpressing rat Kir6.2 and SUR1 subunits, as in insulinoma cell lines. In contrast, zinc exerted an inhibitory action on SUR2A-containing cells. Therefore, SUR1 expression is required for the activating action of zinc, which also depended on extracellular pH and was blocked by diethyl pyrocarbonate, suggesting histidine involvement. The five SUR1-specific extracellular histidine residues were submitted to site-directed mutagenesis. Of them, two histidines (His-326 and His-332) were found to be critical for the activation of K ATP by zinc, as confirmed by the double mutation H326A/H332A. In conclusion, zinc activates K ATP by binding itself to extracellular His-326 and His-332 of the SUR1 subunit. Thereby zinc could exert a negative control on cell excitability and secretion process of pancreatic ␤-and ␣-cells. In fact, we have recently shown that such a mechanism occurs in hippocampal mossy fibers, a brain region characterized, like the pancreas, by an important accumulation of zinc and a high density of SUR1-containing K ATP . K ATP1 channels are tetradimeric complexes of two structurally unrelated subunits (1-4): an inwardly rectifying K ϩ channel subunit (Kir6.x), which serves as an ATP-inhibitable pore (5), and a sulfonylurea receptor subunit (SUR), which belongs to the ATP-binding cassette transporter superfamily and endows the channel with sensitivity to magnesium nucleotides, channel openers, and sulfonylureas (6). To date, two Kir6.x genes have been described, Kir6.1 and Kir6.2 (7-9). As for the SUR subunit, two closely related genes, SUR1 and SUR2, have been cloned with different splice variants such as SUR2A and SUR2B (6,[10][11][12]. Depending on tissues or organs, the different molecular forms of SUR and Kir6.x proteins co-assemble to form K ATP channels with different functional and pharmacological properties (13,14). Cardiac and skeletal muscle K ATP channels are comprised of Kir6.2 and SUR2A, whereas vascular smooth muscle K ATP channels combine the subunit SUR2B with either Kir6.1 or Kir6.2. The pancreatic ␤-cell K ATP channels involved in insulin secretion are comprised of Kir6.2 and SUR1. This pattern is also abundant in the mammalian central nervous system, especially in the hippocampal mossy fiber nerve terminals (15). In addition, several other subunit combinations have been described in the central nervous system (14).Strikingly, several structures possessing K ATP channels of the Kir6.2 and SUR1 type, such as pancreatic ␤-cells and hippocampal mossy fibers, also contain substantial amounts of zinc (16 -18). Puzzled by this co-localization, we found that micromolar concentrations of zinc hyperpolarize ␤-cells from an insulin-secreting pancreatic line (RIN...

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