Glucose and carbachol generate 1,2-diacylglycerols by different mechanisms in pancreatic islets.

Diacylglycerols (DAG) modulate secretory responses by the activation of protein kinase C. Early changes in DAG formation induced by the muscarinic receptor agonist carbachol were compared to those caused by the nutrient secretagogue glucose in pancreatic islets. Turnover rates of DAG were investigated in radiolabeling experiments, whereas changes in total mass and fatty acid composition of DAG were assessed by gas-liquid chromatography. When islet lipids were labeled to steady state in tissue culture with [3H]glycerol, carbachol induced a rapid (10 s) and sustained increase of [3H]DAG generation. In contrast, glucose stimulation failed to increase [3H]glycerol containing DAG, and this was probably due to the isotopic dilution of the label secondary to enhanced glycolysis. This was substantiated by following the transfer of 14C from glucose into DAG. Within 1 min of acute exposure of islets to D-[U-14C]-glucose at stimulatory concentrations, DAG labeling increased fivefold representing up to 2% of total glucose usage. Similar stimulation of 14C incorporation into other neutral lipids and inositol phospholipids was observed, suggesting the enhanced de novo synthesis of phosphatidic acid, the common precursor for DAG, and inositol phospholipids from glycolytic intermediates. Transfer of 14C from glucose was not stimulated by agents such as carbachol and exogenous phospholipase C that act primarily on inositol phospholipid breakdown. The total mass of islet DAG was increased by 60% after both carbachol and glucose stimulation. However, analysis of the fatty acid composition of carbachol-generated DAG revealed at the early time point (10 s) a prevalent stearoyl-arachidonoyl configuration similar to that reported for inositol phospholipids. This pattern shifted to a DAG enriched in palmitic acid at a later time point. Glucose-stimulated islets displayed a predominance of palmitic acid containing DAG, indicating increased de novo synthesis of the putative second messenger rather than its formation by inositol phospholipid hydrolysis. Indeed, steady-state labeling of these phospholipids with [3H]inositol confirmed this idea since only carbachol caused detectable inositol phospholipid hydrolysis. Thus, although protein kinase C may be activated by both carbachol and glucose, the two secretagogues generate diacylglycerols through different mechanisms.

The impact of callosities on the magnitude and duration of plantar pressure in patients with diabetes mellitus. A callus may cause 18,600 kilograms of excess plantar pressure per day.

BACKGROUND: The importance of high peak plantar pressure (PP) in the development of foot ulcer is well known. However, few studies have analyzed the real impact of callosities on plantar pressure and ulcer formation. METHODS: The plantar pressure (PP) in patients with diabetes mellitus was studied in three groups, of a total number of 33 type 2 diabetic patients, without neuropathy or peripheral vascular disease: subjects with callus (A) (n = 10), subjects without callus (B) (n = 10), and a separate group of patients with callus which was submitted to callus removal (C) (n = 13). The plantar pressure (PP) parameters were measured by FSR 174 sensors and computer analyses were performed by LabView. RESULTS: Both maximum peak PP and duration of PP are significantly higher in patients with callus (peak PP: 314 +/- 52 kPa vs 128 +/- 16 kPa, p < 0.005; duration of PP: 621 +/- 27 ms vs 505 +/- 27 ms, p < 0.05). The intervention group C before and after callus removal showed an identical trend. Callus removal has decreased the peak PP by 58% (p < 0.001) and duration of PP has been decreased by 150 milliseconds by step (p < 0.05). CONCLUSION: This study has shown the deleterious role of callus and assuming that an average person walks about 10,000 steps a day, a callus may cause 18,600 kg of excess plantar pressure per day. In addition, this study has proven the importance of early and regular removal of hyperkeratotic tissue. Even more aggressive removal could be recommended in patients with neuropathy and peripheral vascular disease.

A comparison of diabetic foot ulcer patients managed in VHA and non-VHA settings.

OBJECTIVE: To compare patients with diabetes and new onset foot ulcers treated in Veterans Health Administration (VHA) and non-VHA settings. METHODS: The treatment of patients with new onset diabetic foot ulcers was prospectively monitored in three VHA and three non-VHA hospitals and outpatient settings until ulcer healing, amputation, or death. RESULTS: Of the 302 individuals enrolled in this study, 47% were veterans receiving VHA care. There were no significant differences between veterans and nonveterans in baseline wound classification, diabetes severity, or comorbid conditions. Veterans received significantly fewer sharp debridements, total contact casts, and custom inserts than their nonveteran counterparts, and they had significantly more x-rays, local saline irrigations, IV antibiotics, and prescriptions for bed rest. The percentage of amputations was higher in veterans but did not achieve statistical significance. CONCLUSIONS: Many commonly held stereotypes of veteran men were not found. Veterans and nonveterans with foot ulcers were similar in terms of health and foot history, diabetes severity, and comorbid conditions. There was considerable variation in treatment of diabetic foot ulcers between VHA and non-VHA care. Yet this variation did not result in statistically significant differences in ulcer outcomes.

Teaching diabetic foot care effectively.

Patient education is a fundamental aspect of the management of foot ulcers in the patient with diabetes mellitus. Preventive measures have to be focused on the individual risk profile of the patient and on the chronology of appearance of symptoms. Teaching issues need to be adapted into the following three stages: A) before: prevention of foot ulceration in the at-risk patient; B) acute: prevention of extension of an existing ulcer; and C) after: prevention of recurrence.

Two sites for adenine-nucleotide regulation of ATP-sensitive potassium channels in mouse pancreatic beta-cells and HIT cells.

ATP-inhibited potassium channels (K(ATP)) were studied in excised, inside-out patches from cultured adult mouse pancreatic beta-cells and HIT cells. In the absence of ATP, ADP opened K(ATP) channels at concentrations as low as 10 microM and as high as 500 microM, with maximal activation between 10 and 100 microM ADP in mouse beta-cell membrane patches. At concentrations greater than 500 microM, ADP inhibited K(ATP) channels while 10 mM virtually abolished channel activity. HIT cell channels had a similar biphasic response to ADP except that more than 1 mM ADP was required for inhibition. The channel opening effect of ADP required magnesium while channel inhibition did not. Using creatine/creatine phosphate solutions with creatine phosphokinase to fix ATP and ADP concentrations, we found substantially different K(ATP)-channel activity with solutions having the same ATP/ADP ratio but different absolute total nucleotide levels. To account for ATP-ADP competition, we propose a new model of channel-nucleotide interactions with two kinds of ADP binding sites regulating the channel. One site specifically binds MgADP and increases channel opening. The other, the previously described ATP site, binds either ATP or ADP and decreases channel opening. This model very closely fits the ADP concentration-response curve and, when incorporated into a model of beta-cell membrane potential, increasing ADP in the 10 and 100 microM range is predicted to compete very effectively with millimolar levels of ATP to hyperpolarize beta-cells. The results suggest that (i) K(ATP)-channel activity is not well predicted by the "ATP/ADP ratio," and (ii) ADP is a plausible regulator of K(ATP) channels even if its free cytoplasmic concentration is in the 10-100 microM range as suggested by biochemical studies.

[Cost of training a diabetes mellitus patient. Effects on the prevention of amputation]. / Coût de la formation du patient atteint d'un diabète sucré. Effets sur la prévention des amputations.

Cost of disease is a complex notion: financial cost, psychological cost for those who have cope with a chronic disease. But there is also another cost which has not yet sufficiently been taken into account: the cost of resistance to change. It has largely been shown that patient education could result in major cost-saving as well as improvement of quality of life. Why is there such a resistance from health care providers, health policy planners for implementation of patients education programs? These resistances may well be part of the real cost of efficient control of a disease and like in the case of diabetes, prevention of acute and chronic complications. Education and training of patients has enabled us to decrease markedly lower extremities amputations: 12 times less above knee amputations, reduction by half of below knee amputations and a four fold decrease of toe amputations at the University Hospital of Geneva, Switzerland.

Ca2+-mediated generation of inositol 1,4,5-triphosphate and inositol 1,3,4,5-tetrakisphosphate in pancreatic islets. Studies with K+, glucose, and carbamylcholine.

The role of Ca2+ in the generation of inositol phosphates was investigated using rat pancreatic islets after steady state labeling with myo-[2-3H]inositol. Depolarizing K+ concentrations (24 mM) evoked early (2 s) increases in inositol 1,4,5-trisphosphate (Ins-1,4,5-P3) and inositol 1,3,4,5-tetrakisphosphate (Ins-1,3,4,5-P4) as measured by high performance anion-exchange chromatography. The increase in Ins-1,4,5-P3 was transient and was followed by a more pronounced rise in Ins-1,3,4-P3. These effects were dependent on the presence of extracellular Ca2+ but were not secondary to release of either neurotransmitters or metabolites of arachidonic acid. K+ also promoted the breakdown of phosphatidylinositol 4,5-bisphosphate (PtdIns-4,5-P2) and of the other phosphoinositides. Glucose (16.7 mM) was less marked in its effects but still promoted rapid increases in Ins-1,3,4,5-P4 (2 s) and Ins-1,4,5-P3 (10 s) and a slower rise in Ins-1,3,4-P3 (30 s). The levels of all three metabolites rose steadily over 10 min stimulation. These responses to glucose could be largely, although not entirely, inhibited by depletion of extracellular Ca2+ or by Ca2+ channel blockade with verapamil (20 microM). Carbamylcholine (0.5 mM) was the most potent stimulus used evoking early rises in Ins-1,4,5-P3 and Ins-1,3,4,5-P4 (2 s) followed by Ins-1,3,4-P3 (10 s), effects which were only partially dependent on extracellular Ca2+. The results suggest that a Ca2+-mediated PtdIns-4,5-P2 hydrolysis accounts for most of the Ins-1,4,5-P3 generated in response to glucose but not carbamylcholine. In addition, glucose may exert effects on inositol phosphate metabolism which are Ca2+ independent.

Activators of protein kinase C depolarize insulin-secreting cells by closing K+ channels.

Carbohydrate stimuli of insulin secretion depolarize the pancreatic B cell and the B-cell line RINm5F by inhibiting ATP-sensitive K+ channels. We examined the possibility that this effect is mediated by activation of protein kinase C. In RINm5F cells, the triose D-glyceraldehyde evoked a rapid increase of the mass of 1,2-diacylglycerol, the endogenous activator of protein kinase C. This effect is mainly due to de novo synthesis of the lipid from glycolytic intermediates, as glyceraldehyde carbon was incorporated into 1,2-diacylglycerol within 1 min of exposure to 14C-labelled glyceraldehyde. The effects of two exogenous activators of kinase C, 4-beta-12-phorbol-myristate 13-acetate (PMA) and 1,2-didecanoylglycerol (DC10) on single K+ channel currents were examined in RINm5F cell-attached membrane patches. Both PMA and DC10 depolarized the cells and decreased the open-state probability of the ATP-sensitive K+ channels. These actions were not due to changes in cellular ATP content, since PMA, like glyceraldehyde, failed to alter cellular ATP. As is the case for glyceraldehyde, PMA and DC10 raised cytosolic free Ca2+ [( Ca2+]i) and stimulated insulin secretion. Both of these effects are inhibited in the absence of external Ca2+. This, and the attenuation of the [Ca2+]i rise by verapamil, suggest that all three stimuli raise [Ca2+]i by promoting Ca2+ influx through voltage-gated channels in turn leading to insulin secretion. As the exogenous activators of protein kinase C mimic the effects of glyceraldehyde, it is proposed that the carbohydrate-mediated production of 1,2-diacylglycerol constitutes the link between metabolism and membrane depolarization.(ABSTRACT TRUNCATED AT 250 WORDS)