Beta-adrenergic stimulation modulation of heart rate via synchronization of ryanodine receptor Ca2+ release

A robust "fight or flight response", largely mediated via acute beta-adrenergic receptor (beta-AR) stimulation to the heart to increase its beating rate and contractile performance, is an essential component of the vertebrate survival instinct. While it has long been recognized that activation of beta-AR increases the spontaneous beating rate of sinoatrial nodal cells (SANC), specific links between stimulation of beta-ARs and the resultant increase in firing rate have not been evaluated. Our recent studies employed imaging of subcellular Ca2+ release coupled with recording of membrane potential or current in single, isolated cardiac SANC, to seek novel links between beta-AR stimulation and ryanodine receptor Ca2+ release and heart rate. An overview of these recent results, which provides novel insights into mechanisms of cardiac reserve that underlie the "fight or flight instinct, is presented here.     

Morphological and functional studies on submucosal islet transplants in normal and diabetic hamsters

The long-term outcome of human islet allotransplantation is poor, and it remains to be seen if the Edmonton Protocol will make a positive impact upon the extension of posttransplant islet function. Hence, establishing an implantation site capable of sustaining islet allografts for a prolonged duration needs to be explored. In this study we investigated the submucosal space of the duodenum in Syrian golden hamsters. Following transplantation of more than 800 islets into streptozotocin (STZ)-induced diabetic hamsters, basal nonfasted blood glucose levels decreased from 403 +/- 14 to 143 +/- 10 mg/dl within 5 weeks posttransplantation. In these animals, in vivo islet function, as determined by intravenous glucose tolerance test (IVGTT), was similar to nondiabetic controls (K values: 1.16 +/- 0.12 vs. 0.95 +/- 0.06, respectively) and was significantly greater than diabetic controls (K value: 0.47 +/- 0.07). Islets transplanted into the submucosal space become richly vascularized within 2 weeks, and there is minimal host inflammatory infiltrate. The beta-cells of the graft remain well granulated with insulin for at least 129 days. We conclude that the submucosal space is an effective engraftment site for islets that warrants further development in a large-animal model.     

Clinical picture of open-angle glaucoma in patients with critical stenosis of the internal carotid artery

Clinical picture of primary open-angle glaucoma (POAG) was studied in 32 patients (57 eyes) with pronounced stenosis of the extracranial segment of the internal carotid artery (ICA) on the side of the glaucomatous eye. Major clinical signs were detected: conjunctival angiopathy, pronounced diffuse dystrophy of the iris, absence of pigmented iridal rim, pseudoexfoliations, pale optic disk with saucer-like excavation of different severity. Intraocular pressure (IOP) was 26-34 mm Hg and could not be normalized by drug therapy or antiglaucomatous surgery. Ultrasonic methods for examination of the eyeball vessels showed pronounced decrease of the bloodflow velocity and a significant increase of resistance index in the orbital and central retinal arteries. Reconstructive operations on the carotid arteries performed in POAG patients for critical stenosis of ICA improved the eyeball hemoperfusion and decreased IOP.     

Using protein design for homology detection and active site searches

We describe a method of designing artificial sequences that resemble naturally occurring sequences in terms of their compatibility with a template structure and its functional constraints. The design procedure is a Monte Carlo simulation of amino acid substitution process. The selective fixation of substitutions is dictated by a simple scoring function derived from the template structure and a multiple alignment of its homologs. Designed sequences represent an enlargement of sequence space around native sequences. We show that the use of designed sequences improves the performance of profile-based homology detection. The difference in position-specific conservation between designed sequences and native sequences is helpful for prediction of functionally important residues. Our sequence selection criteria in evolutionary simulations introduce amino acid substitution rate variation among sites in a natural way, providing a better model to test phylogenetic methods.     

Update of clinical trials from the American College of Cardiology 2003. EPHESUS,SPORTIF-III,ASCOT, COMPANION,UK-PACE and T-wave alternans

The American College of Cardiology provided much useful new information to inform those who care for patients with heart failure about what they should and should not adopt into current clinical practice. The EPHESUS trial suggests a much wider role for aldosterone antagonists for the management of heart failure and left ventricular systolic dysfunction. SPORTIF-III indicates we may have a safer, simpler warfarin substitute soon. ASCOT reinforces the potential futility of statin therapy unless it is well targeted. The results of the COMPANION study investigating cardiac resynchronisation devices and implantable defibrillators were encouraging but inconclusive and/or hard to interpret. UK-PACE again questions the use of dual chamber pacing. T-wave alternans is an interesting experimental technique that may be useful in selecting which patients need an implantable defibrillator, although the technology needs testing in an appropriate patient population.     

Sympathetic nervous system plays a major role in acute cold/restraint stress inhibition of host resistance to Listeria monocytogenes

BALB/c mice exposed to acute cold/restraint stress (ACRS) had significantly lower host resistance to Listeria monocytogenes (LM) than controls. The stress hormones corticosterone (CORT) and norepinephrine (NE), which are known to modulate immune responses, were evaluated as the cause of the decline in immune defense. The involvement of CORT and NE was investigated by pretreating mice with the CORT synthesis inhibitor metyrapone and the chemical sympathectomy drug 6-hydroxydopamine (6-OHDA), respectively. LM burdens in spleen and liver were determined three days post-infection. 6-OHDA significantly decreased the LM burden in both control and stressed animals. 6-OHDA also completely blocked the stress effects observed in spleens while only partially affecting the liver. The 6-OHDA-uptake inhibitor desipramine aided confirmation that peripheral sympathetic adrenergic nerves and NE depletion, rather than the direct action of 6-OHDA, were responsible for the decreased susceptibility to LM. The results suggest that the peripheral sympathetic nervous system (SNS) postganglionic neurotransmitter NE plays a major role in LM host resistance and has significant tissue-dependent effects after ACRS. In contrast, metyrapone-treated animals had further decreased host resistance to LM, suggesting a potential protective effect of CORT after ACRS. Altogether, the results suggest that stress hormones play an important role in stress-modulated host resistance and that NE is the major hormone involved in ACRS-induced suppression of host resistance.     

Tumoral distribution of long-circulating dextran-coated iron oxide nanoparticles in a rodent model

PURPOSE: To investigate the accumulation and cellular uptake of long-circulating dextran-coated iron oxide (LCDIO) particles in malignant neoplasms in vivo. MATERIALS AND METHODS: A gliosarcoma rodent model was established to determine the distribution of a model LCDIO preparation in tumors. LCDIO accumulation in tissue sections was evaluated with multichannel fluorescence microscopy with rhodaminated LCDIO, green fluorescent protein as a tumor marker, and Hoechst 33258 dye as an intravital endothelial stain. Uptake into tumor cells was corroborated with results of immunohistochemical and cell culture uptake experiments. The effect of intratumoral LCDIO uptake on magnetic resonance (MR) imaging signal intensity was evaluated with a 1.5-T superconducting magnet. RESULTS: Tumoral accumulation of LCDIO was 0.11% +/- 0.06 of the injected dose per gram of tissue in brain tumors and was sufficient for detection at MR imaging. In tumor sections, LCDIO was preferentially localized in tumor cells (49.0% +/- 4.6) but was also taken up by macrophages in tumors (21.0% +/- 3.1) and by endothelial cells in the areas of active angiogenesis (6.5% +/- 1.4). In cell culture, LCDIO uptake was strongly correlated with growth rate of tumor cell lines. CONCLUSION: Tumoral LCDIO accumulation was not negligible and helped explain MR imaging signal intensity changes observed in clinical trials. Microscopically, LCDIO accumulated predominantly in tumor cells and tumor-associated macrophages. Uptake into tumor cells appeared to be directly proportional to cellular proliferation rates.     

Electro-impulse therapy in combined treatment of patients with thyrotoxic goiter complicated by cardiac fibrillation

Cardiac fibrillation was revealed at admission in 260 (5.2%) of 4996 patients who were to undergo subtotal resection of thyroid gland for toxic goiter. In 114 (43.8%) patients sinus rhythm was restored with drugs in preoperative period. Electroimpulse therapy was carried out in other 146 patients which was effective in 89% cases. Efficacy of electroimpulse therapy depended mainly on the arrhythmia duration. Restoration of sinus rhythm before operation in patients with toxic goiter improves conditions of preoperative preparation and decreases the risk of surgical treatment. There were no lethal outcomes.     

Inhibition of the slow response action potential during the aftercontraction in mammalian heart muscle

In experiments on isolated guinea-pig papillary muscles the excitability of the cellular membrane was investigated during the aftercontractions (ACs) induced by lowering the perfusate temperature to 15°C, addition of noradrenaline (10^?5m) and raising CaCl₂ to 15 mm. No changes in membrane potential were observed during ACs. At stimulation rate of 0.2 Hz the amplitude of the first AC was 21 ± 3% (n = 6) of the main twitch and the peak of this AC appeared after the peak of the main twitch with delay of 1.6 ± 0.2 s. The recovery process for maximal upstroke rate of action potential and the strength-interval curve were shown to proceed without any transients during AC. This indicates that an increase of intracellular Ca²⁺ concentration during AC has no effects on the fast Na⁺ channel activity. The slow response action potentials recorded in the high K⁺ (25 mm) were decreased significantly during AC. The reduction of slow response amplitude during AC could not be explained by the increase of threshold only because even at supramaximal intensity of stimulation this reduction was still visible and equal to 22 ± 1 mV. It was concluded that a slow channel activity of cardiac membrane might depend on the intracellular Ca²⁺ concentration and thereby be determined by the efficiency of Ca²⁺ sequestering systems in the cell. Caffeine (2 mm) abolished the ACs. After-releases of Ca²⁺ from sarcoplasmic reticulum were suggested as the causes of these ACs.