Long-chain CoA esters activate human pancreatic beta-cell KATP channels: potential role in Type 2 diabetes.

AIMS/HYPOTHESIS: The ATP-regulated potassium (KATP) channel in the pancreatic beta cell couples the metabolic state to electrical activity. The primary regulator of the KATP channel is generally accepted to be changes in ATP/ADP ratio, where ATP inhibits and ADP activates channel activity. Recently, we showed that long-chain CoA (LC-CoA) esters form a new class of potent KATP channel activators in rodents, as studied in inside-out patches. METHODS: In this study we have investigated the effects of LC-CoA esters in human pancreatic beta cells using the inside-out and whole-cell configurations of the patch clamp technique. RESULTS: Human KATP channels were potently activated by acyl-CoA esters with a chain length exceeding 12 carbons. Activation by LC-CoA esters did not require the presence of Mg2+ or adenine nucleotides. A detailed characterization of the concentration-dependent relationship showed an EC50 of 0.7+/-0.1 micromol/l. Furthermore, in the presence of an ATP/ADP ratio of 10 (1.1 mmol/l total adenine nucleotides), whole-cell KATP channel currents increased approximately six-fold following addition of 1 micro mol/l LC-CoA ester. The presence of 1 micro mol/l LC-CoA in the recording pipette solution increased beta-cell input conductance, from 0.5+/-0.2 nS to 2.5+/-1.3 nS. CONCLUSION/INTERPRETATION: Taken together, these results show that LC-CoA esters are potent activators of the KATP channel in human pancreatic beta cells. The fact that LC-CoA esters also stimulate KATP channel activity recorded in the whole-cell configuration, points to the ability of these compounds to have an important modulatory role of human beta-cell electrical activity under both physiological and pathophysiological conditions.

Impaired proliferation and increased L-lactate production of dermal fibroblasts in the GK-rat, a spontaneous model of non-insulin dependent diabetes mellitus.

Intact fibroblast function is required for normal wound healing. Although healing is generally accepted to be disturbed in non-insulin dependent diabetes mellitus, the signals modulating this disturbance are not fully understood. Therefore, we studied dermal fibroblasts from the GK rat, a non-insulin dependent diabetes mellitus model, and the Wistar rat (control) regarding growth characteristics, and L-lactate production at 5.5 mM and 25.5 mM glucose in the absence or presence of protein kinase C-inhibition, or alpha-tocopherol acetate. In addition, growth and L-lactate responses to hyaluronic acid were assessed under normal glucose conditions. At 5.5 mM glucose, the fibroblasts from the GK rat showed a lower proliferation rate during the first 24 hours, measured as DNA content, as compared to Wistar rats, i.e. at 8 hours GK was 57% of control, p < 0.01, at 24 hours GK was 60% of control, p < 0.01. The GK rat fibroblasts accumulated higher L-lactate levels in the media at 24-96 hours. Addition of glucose at a concentration of 25.5 mM decreased the total DNA content in GK rat fibroblast cultures to 74% (p < 0.05) and in control to 87% (p < 0.05), and increased L-lactate levels, measured at 48 hours. A protein kinase C-inhibitor, bisindolylmaleimide IX, increased DNA content and decreased L-lactate in both cell types during culture in high glucose, but only affected GK rat fibroblasts during normal glucose. Hyaluronic acid, increased DNA content in both types of fibroblasts, GK: 139% (p < 0.05), control: 127% (p < 0.05) and reduced L-lactate production. The above observations indicate that GK rat fibroblast proliferation is suppressed when the cells are cultured in high glucose containing media. In addition, protein kinase C and hyaluronic acid might play a role as modulators of fibroblast proliferation during the diabetic state.

Family history of diabetes in middle-aged Swedish men is a gender unrelated factor which associates with insulinopenia in newly diagnosed diabetic subjects.

We have investigated the association of a family history of diabetes with glucose tolerance in a population of Swedish men. All men 35-54 years of age in 1992 and living in four different local municipalities of the outer Stockholm area were screened by questionnaire. From 10236 completed questionnaires 1622 men, selected for presence of such a history but without known diabetes, as well as 1507 men without a family history underwent an oral glucose tolerance test. Diabetes (2 h-plasma glucose levels > 11.0 mmol/l) was detected in 55 and impaired glucose tolerance (plasma glucose levels 7.8-11.0 mmol/l) in 172 subjects. The odds ratio of diabetes, associated with a family history, was 4.1, confidence interval 2.1-8.3 and for impaired glucose tolerance 1.6, confidence interval 1.2-2.3. Influence of a family history was measurable also within the range of normal 2-h glucose concentrations: compared to 2-h glucose levels < 3.8 mmol/l; the odds ratio associated with a family history was 1.4, confidence interval 1.1-1.7 and 1.3, confidence interval 1.1-1.6 for concentrations 4.8-5.7 mmol/l and 5.8-7.7 mmol/l respectively. The odds ratio of diabetes and impaired glucose tolerance among men with a family history increased with number and closeness of relatives with diabetes but was not affected by the gender of the family member. Overweight (BMI > 25.0 kg/m2) increased the odds ratio of diabetes in subjects with a family history, the odds ratio being 24, confidence interval 3-177, when both conditions were present. In subjects with Type II (non-insulin-dependent) diabetes mellitus discovered during the investigation, the presence of a family history of diabetes was associated with decreased insulin secretion rather than insulin resistance as assessed by fasting insulin, homeostasis model assessment, and the 2-h insulin response to the oral glucose tolerance test. We conclude that a family history of diabetes strongly but independently of gender associates with decreased glucose tolerance. Furthermore, the results are compatible with a major role for low insulin secretion in the diabetogenic influence of a family history of diabetes in middle-aged Swedish men. Lastly, the very high risk for diabetes in middle-aged men with both a family history of diabetes and obesity indicates that such people should, for the purpose of therapeutic intervention, be identified in the general population.

Generalized presence of a PEC-60-like peptide in catecholamine neurones.

PEC-60, a 60-residue intestinal peptide structurally related to the pancreatic secretory type of trypsin inhibitor, has been isolated, characterized and molecularly cloned. It shows biological activity as a hormone in both the gastrointestinal tract and in the immune system. We now report immunohistochemical evidence suggesting its neural localization exclusively within central and peripheral catecholamine (CA) neurones. PEC-60-like immunoreactivity was present in cell bodies, dendrites and nerve terminals of virtually all catecholamine neurones examined and including the noradrenergic gland cells of the adrenal medulla. PEC-60-like immunoreactivity was not seen, however, within the tyrosine hydroxylase-positive but CA-negative arcuate neurones producing growth hormone releasing hormone. The findings open up the possibility that a PEC-60-like peptide may represent a generalized co-transmitter in the peripheral and central CA neurones.

Difference in calcium dependency of insulin, glucagon and somatostatin secretion in response to glibenclamide in perfused rat pancreas.

The extracellular calcium requirements for insulin, glucagon and somatostatin release induced by 1 microgram/ml of glibenclamide have been compared in the perfused, isolated rat pancreas. In the absence of glucose, the drug evoked insulin release equally well at physiological (2.6 mmol/l) and low (0.25 mmol/l) levels of total calcium. In contrast, glibenclamide evoked somatostatin release at 2.6 but not at 0.25 mmol/l of calcium. At 2.6 mmol/l of calcium, glibenclamide evoked bimodal effects (stimulation followed by inhibition) on glucagon secretion. At 0.25 mmol/l of calcium, basal secretory rates of glucagon were elevated and a small stimulatory effect of glibenclamide was seen. Addition of 0.5 mmol/l of EGTA to media with low calcium concentrations uniformly abolished the A, B and D cell secretory responses to glibenclamide. The possible modulation of calcium dependency by a non-stimulatory concentration of glucose was tested by its addition at 3.3 mmol/l to the perfusion media. Glucose enhanced glibenclamide-induced insulin secretion, both at 0.25 and 2.6 mmol/l of calcium. However, at 0.25 mmol/l of calcium, the enhancing effect of glucose was more pronounced than at 2.6 mmol/l. At 2.6 mmol/l of calcium, glucose diminished the somatostatin and abolished the glucagon response to glibenclamide. At 0.25 mmol/l of calcium, glucose did not influence somatostatin release while the presence of the sugar diminished basal and glibenclamide-induced glucagon secretion. The present data confirm the requirement of extracellular calcium for A, B and D cell secretion, demonstrating different calcium dependencies for the cell types and indicate that this dependency can, in part, be modulated by glucose.

Utilization of glucose by the implanting mouse blastocyst activated by oestrogen.

Blastocysts from mice in an experimental delay of implantation increased their oxidation rate of both glucose and fructose when implantation was initiated by an injection of oestrogen. About 18 h after the injection, the rate of glucose oxidation was significantly higher than that of fructose oxidation. Simultaneously with the increase in the rate of glucose oxidation, glycogen granules appeared in the trophoblast cells. In uterine flushings, the amount of glucose increased already at 6 h. This time corresponds to the period when the blastocyst gets activated for implantation. Determination of glucose utilization by the blastocysts demonstrated that 3 h after the oestrogen injection, the utilization was low but that it was markedly increased at 6 and 18 h. It is concluded that at the initiation of implantation, mouse blastocysts prefer glucose to fructose and that the presence of glucose in the secretion and the increased utilization of glucose by blastocysts at this time suggest that this substrate could be one important nutrient for the blastocyst at early implantation. Glucose, however, cannot be the sole factor critical for the activation of the delayed blastocyst.