Frontiers in physiology
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Frontiers in physiology · Jan 2014
ReviewRole of sinoatrial node architecture in maintaining a balanced source-sink relationship and synchronous cardiac pacemaking.
Normal heart rhythm (sinus rhythm) depends on regular activity of the sinoatrial node (SAN), a heterogeneous collection of specialized myocytes in the right atrium. SAN cells, in general, possess a unique electrophysiological profile that promotes spontaneous electrical activity (automaticity). However, while automaticity is required for normal pacemaking, it is not necessarily sufficient. ⋯ Here, we review the important structural features of the SAN with a focus on how these elements help manage a precarious balance between electrical charge generated by the SAN ("source") and the charge needed to excite the surrounding atrial tissue ("sink"). We also discuss how compromised "source-sink" balance due, for example to fibrosis, may promote SAN dysfunction, characterized by slow and/or asynchronous pacemaker activity and even failure, in the setting of cardiovascular disease (e.g., heart failure, atrial fibrillation). Finally, we discuss implications of the "source-sink" balance in the SAN complex for cell and gene therapies aimed at creating a biological pacemaker as replacement or bridge to conventional electronic pacemakers.
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Frontiers in physiology · Jan 2014
ReviewEncapsulating peritoneal sclerosis-a rare but devastating peritoneal disease.
Encapsulating peritoneal sclerosis (EPS) is a devastating but, fortunately, rare complication of long-term peritoneal dialysis. The disease is associated with extensive thickening and fibrosis of the peritoneum resulting in the formation of a fibrous cocoon encapsulating the bowel leading to intestinal obstruction. The incidence of EPS ranges between 0.7 and 3.3% and increases with duration of peritoneal dialysis therapy. ⋯ The process of epithelial-mesenchymal transition of mesothelial cells is proposed to play a central role in the development of peritoneal sclerosis, a common characteristic of patients on dialysis, however, its importance in EPS is less clear. There is no established treatment for EPS although evidence from small case studies suggests that corticosteroids and tamoxifen may be beneficial. Nutritional support is essential and surgical intervention (peritonectomy and enterolysis) is recommended in later stages to relieve bowel obstruction.
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The role of astrocytes in brain function has evolved over the last decade, from support cells to active participants in the neuronal synapse through the release of "gliotransmitters."Astrocytes express receptors for most neurotransmitters and respond to them through Ca(2+) intracellular oscillations and propagation of intercellular Ca(2+) waves. While such waves are able to propagate among neighboring astrocytes through gap junctions, thereby activating several astrocytes simultaneously, they can also trigger the release of gliotransmitters, including glutamate, d-serine, glycine, ATP, adenosine, or GABA. There are several mechanisms by which gliotransmitter release occurs, including functional hemichannels. ⋯ In consequence, hemichannels could play a pivotal role in astrocyte-to-astrocyte communication and astrocyte-to-neuron cross-talk. Recent evidence suggests that astroglial hemichannels are involved in higher brain functions including memory and glucose sensing. The present review will focus on the role of hemichannels in astrocyte-to-astrocyte and astrocyte-to neuron communication and in brain physiology.
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Frontiers in physiology · Jan 2014
ReviewCLC channel function and dysfunction in health and disease.
CLC channels and transporters are expressed in most tissues and fulfill diverse functions. There are four human CLC channels, ClC-1, ClC-2, ClC-Ka, and ClC-Kb, and five CLC transporters, ClC-3 through -7. Some of the CLC channels additionally associate with accessory subunits. ⋯ Mutations in CLCN2 were found in patients with CNS disorders but the functional role of this isoform is still not understood. Recent links between ClC-1 and epilepsy and ClC-Ka and heart failure suggested novel cellular functions of these proteins. This review aims to survey the knowledge about physiological and pathophysiological functions of human CLC channels in the light of recent discoveries from biophysical, physiological, and genetic studies.
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Frontiers in physiology · Jan 2014
ReviewSystematic review of near-infrared spectroscopy determined cerebral oxygenation during non-cardiac surgery.
Near-infrared spectroscopy (NIRS) is used to monitor regional cerebral oxygenation (rScO2) during cardiac surgery but is less established during non-cardiac surgery. This systematic review aimed (i) to determine the non-cardiac surgical procedures that provoke a reduction in rScO2 and (ii) to evaluate whether an intraoperative reduction in rScO2 influences postoperative outcome. The PubMed and Embase database were searched from inception until April 30, 2013 and inclusion criteria were intraoperative NIRS determined rScO2 in adult patients undergoing non-cardiac surgery. ⋯ Following thoracic surgery, major orthopedic, and abdominal surgery the occurrence of postoperative cognitive dysfunction (POCD) might be related to intraoperative cerebral desaturation. In conclusion, certain non-cardiac surgical procedures is associated with an increased risk for the occurrence of rScO2. Evidence for an association between cerebral desaturation and postoperative outcome parameters other than cognitive dysfunction needs to be established.