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Recent studies have shown that two different voltage-dependent Ca2+ channels are expressed in pancreatic islets, the beta-cell/neuroendocrine-brain and the cardiac subtypes. The effects of chronic hyperglycemia on the levels in pancreatic islets of the mRNAs encoding the alpha 1-subunits of the beta-cell and cardiac subtype Ca2+ channels were studied in rats made hyperglycemic by infusion of glucose for 48 h. A competitive reverse transcriptase-polymerase chain reaction procedure was used to obtain quantitative data on the levels of these two transcripts in islets obtained from individual rats. The quantitative polymerase chain reaction data indicate that the levels of mRNA encoding the alpha 1-subunit of the beta-cell Ca2+ channel are 2.5-fold greater than those for the cardiac subtype. The levels of beta-cell Ca2+ channel mRNA were 72.9% lower in the glucose-infused animals when compared with the saline-infused animals (P < 0.005) and those of the cardiac channel were 72.1% lower in the animals infused with glucose (P < 0.02). In contrast, glucose infusion resulted in a twofold increase in insulin mRNA levels and did not significantly alter levels of beta-actin mRNA. In situ hybridization studies revealed that the mRNAs for these two Ca2+ channels are expressed at higher levels in normal rat islets than in the surrounding acinar tissue, which suggests that the observed changes in mRNA levels occur within cells of the pancreatic islet. To assess the possible functional consequences of this reduction in expression of mRNA for the Ca2+ channels, the insulin secretory responses of perfused pancreases to the Ca2+ channel agonist Bay K8644 were studied.(ABSTRACT TRUNCATED AT 250 WORDS)

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Thrombomodulin (TM) is a membrane protein in the vascular endothelium, and it plays an important role as a cofactor in the thrombin-catalyzed activation of protein C. It has also been found in human plasma; however, its clinical significance is not known. In this study, fasting plasma TM concentrations in 67 diabetic patients with different degrees of albuminuria (39 men aged 57 +/- 8 yr, 28 women aged 57 +/- 11 yr; means +/- SD) and 34 age- and sex-matched healthy subjects were investigated by use of a one-step sandwich enzyme immunoassay, a new method developed by H.I. and others. As a screening, the patients were divided into three groups according to the first morning urinary concentrations of albumin: group 1, less than 30 micrograms/ml (normoalbuminuria); group 2, 30-140 micrograms/ml (microalbuminuria); group 3, greater than 140 micrograms/ml (clinical nephropathy). There was no significant difference in plasma TM level between the control group (17.7 +/- 3.7 ng/ml, n = 34) and group 1 (16.9 +/- 3.4 ng/ml, n = 30); however, plasma TM concentrations in group 2 (22.8 +/- 3.4 ng/ml, n = 22) and group 3 (29.6 +/- 6.1 ng/ml, n = 15) increased significantly compared with those in the control group and group 1, respectively. As a further investigation, three timed overnight urine collections were made. The patients were allocated to three groups according to their rates of albumin excretion: group I, less than 20 micrograms/min (normoalbuminuria); group II, 20-200 micrograms/min (microalbuminuria); group III greater than 200 micrograms/min (clinical nephropathy).(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of the genes for voltage-dependent calcium channels (VDCCs), glucose transporter-2 (GLUT2), and glucokinase was studied in pancreatic islets obtained from normal rats after periods of fasting and refeeding using a competitive polymerase chain reaction procedure. A 72-h fast induced about a 3-fold decrease in the beta-cell/neuroendocrine type VDCC alpha 1-subunit and GLUT2 messenger RNA (mRNA) levels and about a 2-fold decrease in insulin and glucokinase mRNA levels compared to those in fed and refed rats. No significant differences were found in beta-actin and the cardiac-type VDCC alpha 1-subunit mRNA levels among fed, fasted, anf refed rats. We also studied insulin secretion from the isolated perfused pancreata obtained from these animals. We found an elevated threshold and decreased insulin release in response to a stepwise increase in glucose concentrations in the isolated perfused pancreata obtained from fasted rats. Fasting also resulted in a dramatic decrease in insulin secretory responses during the application of an L-type VDCC agonist, Bay K8644 (1 microM). Furthermore, fasting resulted in a significant decrease in both 45Ca2+ uptake by the isolated islets and insulin release from the islets. A strong positive correlation was observed between glucose-induced 45Ca2+ uptake and insulin output among the animals studied. On the other hand, after a 24-h refeeding, significant increases in the insulin secretory response to glucose and Bay K8644 were found, with a normalization in mRNA levels for these components. It, thus, appears that the alterations in beta-cell sensitivity to glucose that occur with fasting and refeeding are the result of complex metabolic alterations in the islet associated with reductions in expression of at least in part the beta-cell/neuroendocrine type VDCC in addition to two components of the glucose-sensing apparatus, including glucokinase and GLUT2, and the reduction in mRNA for insulin.

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The relationship between apolipoprotein E (apoE) polymorphism and plasma lipids and hyperlipemia was investigated in 105 male type II diabetics and 111 male nondiabetics. ApoE phenotypes were determined by a one-dimensional rapid flat gel isoelectric focusing method as described previously. The apoE phenotype frequency in diabetics was similar to that in nondiabetics. The frequency of hyperlipemia was higher in diabetics (56.2%) than in nondiabetics (32.4%). It was highest in the apoE3/2 group of diabetics and nondiabetics, followed by the apoE4/3 and apoE3/3 groups in the order described, indicating that the susceptibility to hyperlipemia differs among the apoE phenotype groups. ApoE3/2 diabetics had significantly higher levels of apoE and very-low-density lipoprotein (VLDL) cholesterol (chol)/VLDL triglyceride (TG) ratios than apoE3/3 diabetics. The effects of diabetes mellitus on plasma lipid levels differed among the various apoE phenotype groups: i.e., plasma total chol and low-density lipoprotein (LDL) chol increased only in apoE3/2 and apoE4/3 diabetics and plasma high-density lipoprotein chol decreased only in apoE3/3 diabetics, as compared with the corresponding apoE phenotype groups of nondiabetics, whereas plasma TG, VLDL TG, and VLDL chol increased in the three apoE phenotype diabetics. Furthermore, an increase of apoEII:apoEIII ratio was observed in apoE3/3 diabetics, particularly in those with hypertriglyceridemia. This study has also shown that the increased apoEII:apoEIII ratio is due to increased sialation of apoE based on the study of sialidase digestion of apo VLDL.(ABSTRACT TRUNCATED AT 250 WORDS)