Time-dependent alterations in rat macrovessels with type 1 diabetes.

Vascular complications are associated with the progressive severity of diabetes, resulting in significant morbidity and mortality. This study quantifies functional vascular parameters and macrovascular structure in a rat model of type 1 diabetes. While there was no difference in the systemic arterial elastance (Ea) with 50 days of diabetes, changes were noted in the aorta and femoral artery including increased tunica media extracellular matrix content, decreased width of both the media and individual smooth muscle cell layers, and increased incidence of damaged mitochondria. Extracellular matrix proteins and elastin levels were significantly greater in the aorta of diabetic animals. These differences correlated with diminished matrix metalloprotease activity in the aorta of the diabetic animals. In conclusion, diabetes significantly altered the structure and ultrastructure of the aorta and femoral artery before systemic changes in arterial elastance could be detected.

Intracellular Ca2+ regulating proteins in vascular smooth muscle cells are altered with type 1 diabetes due to the direct effects of hyperglycemia.

BACKGROUND: Diminished calcium (Ca2+) transients in response to physiological agonists have been reported in vascular smooth muscle cells (VSMCs) from diabetic animals. However, the mechanism responsible was unclear. METHODOLOGY/PRINCIPAL FINDINGS: VSMCs from autoimmune type 1 Diabetes Resistant Bio-Breeding (DR-BB) rats and streptozotocin-induced rats were examined for levels and distribution of inositol trisphosphate receptors (IP3R) and the SR Ca2+ pumps (SERCA 2 and 3). Generally, a decrease in IP3R levels and dramatic increase in ryanodine receptor (RyR) levels were noted in the aortic samples from diabetic animals. Redistribution of the specific IP3R subtypes was dependent on the rat model. SERCA 2 was redistributed to a peri-nuclear pattern that was more prominent in the DR-BB diabetic rat aorta than the STZ diabetic rat. The free intracellular Ca2+ in freshly dispersed VSMCs from control and diabetic animals was monitored using ratiometric Ca2+ sensitive fluorophores viewed by confocal microscopy. In control VSMCs, basal fluorescence levels were significantly higher in the nucleus relative to the cytoplasm, while in diabetic VSMCs they were essentially the same. Vasopressin induced a predictable increase in free intracellular Ca2+ in the VSMCs from control rats with a prolonged and significantly blunted response in the diabetic VSMCs. A slow rise in free intracellular Ca2+ in response to thapsigargin, a specific blocker of SERCA was seen in the control VSMCs but was significantly delayed and prolonged in cells from diabetic rats. To determine whether the changes were due to the direct effects of hyperglycemica, experiments were repeated using cultured rat aortic smooth muscle cells (A7r5) grown in hyperglycemic and control conditions. In general, they demonstrated the same changes in protein levels and distribution as well as the blunted Ca2+ responses to vasopressin and thapsigargin as noted in the cells from diabetic animals. CONCLUSIONS/SIGNIFICANCE: This work demonstrates that the previously-reported reduced Ca2+ signaling in VSMCs from diabetic animals is related to decreases and/or redistribution in the IP3R Ca2+ channels and SERCA proteins. These changes can be duplicated in culture with high glucose levels.

Spontaneous Ca2+ oscillations in subcellular compartments of vascular smooth muscle cells rely on different Ca2+ pools.

Spontaneous Ca2+ oscillations in vascular smooth muscle cells have been modeled using a single Ca2+ pool. This report describes spontaneous Ca2+ oscillations dependent on two separate Ca2+ sources for the nuclear versus cytoplasmic compartments. Changes in free intracellular Ca2+ were monitored with ratiometric Ca2+- fluorophores using confocal microscopy. On average, spontaneous oscillations developed in 79% of rat aortic smooth muscle cells that were synchronous between the cytoplasm and nucleus. Reduction of extracellular Ca2+ (less than 1 microM)decreased the frequency and amplitude of the cytoplasmic oscillations with 48% of the oscillations asynchronous between the nuclear and cytoplasmic compartments. Similar results were obtained with the Ca2+ channel blockers, nimodipine and diltiazem. Arg-vasopressin (AVP) induced a rapid release of intracellular Ca2+ stores that was greater in the nuclear compartment (4.20 +/- 0.23 ratio units, n = 56) than cytoplasm (2.54 +/- 0.28) in cells that had spontaneously developed prior oscillations. Conversely, cells in the same conditions lacking oscillations had a greater AVP-induced Ca2+ transient in the cytoplasm (4.99 +/- 0.66, n = 17) than in the nucleus (2.67 +/- 0.29). Pre-treatment with Ca2+ channel blockers depressed the AVP responses in both compartments with the cytoplasmic Ca2+ most diminished. Depletion of internal Ca2+ stores prior to AVP exposure blunted the nuclear response, mimicking the response of cells that lacked prior oscillations. Spontaneous oscillating cells had a greater sarcoplasmic reticulum network than cells that did not oscillate. We propose that spontaneous nuclear oscillations rely on perinuclear sarcoplasmic reticulum stores, while the cytoplasmic oscillations rely on Ca2+ influx.

Exercise attenuates diabetes-induced ultrastructural changes in rat cardiac tissue.

INTRODUCTION/PURPOSE: Exercise is an effective nonpharmacological treatment in the prevention of mortality and morbidity due to cardiovascular disease in Type I diabetes. This study sought to explore the effects of endurance exercise on the ultrastructural changes seen in diabetic cardiomyopathy. METHODS: Seven-week-old rats were divided into three groups consisting of sedentary nondiabetic control, sedentary diabetic, and exercised diabetic animals. Diabetes was induced using streptozotocin injection, and the exercised animals were run daily on a treadmill for 9 wk. Changes in heart ultrastructure were analyzed using transmission electron microscopy. RESULTS: Ultrastructural changes in the left ventricle produced by diabetes included changes in myofibrillar arrangements, disrupted mitochondria, and increased cytoplasmic area with an increase in lipid amounts and an increase in individual collagen fiber cross-sectional surface area. Also, an increase in heterochromatin lining the nuclear envelope and an increase in invaginations of the nuclear membrane were observed in cardiomyocytes from diabetic rats when compared with the nuclei from nondiabetic cells. Exercise was found to significantly attenuate the diabetes-induced changes in collagen fibrils, cytoplasmic area, and level of mitochondrial disruption. In contrast, exercise did not appear to significantly influence myofibril volume density, lipid accumulation, or nuclear deformities. CONCLUSION: These findings indicate that exercise restores specific ultrastructural characteristics of diabetic cardiomyopathy returning them toward nondiabetic phenotypes, particularly in the mitochondria and extracellular matrix proteins.