Protein kinase C inhibits the transplasma membrane influx of Ca2+ triggered by 4-aminopyridine in Jurkat T lymphocytes

Contribution of electromechanical coupling between Kv and Ca v1.2 channels to coronary dysfunction in obesity

Previous investigations indicate that diminished functional expression of voltage-dependent K(+) (KV) channels impairs control of coronary blood flow in obesity/metabolic syndrome. The goal of this investigation was to test the hypothesis that KV channels are electromechanically coupled to CaV1.2 channels and that coronary microvascular dysfunction in obesity is related to subsequent increases in CaV1.2 channel activity. Initial studies revealed that inhibition of KV channels with 4-aminopyridine (4AP, 0.3 mM) increased intracellular [Ca(2+)], contracted isolated coronary arterioles and decreased coronary reactive hyperemia. These effects were reversed by blockade of CaV1.2 channels. Further studies in chronically instrumented Ossabaw swine showed that inhibition of CaV1.2 channels with nifedipine (10 μg/kg, iv) had no effect on coronary blood flow at rest or during exercise in lean swine. However, inhibition of CaV1.2 channels significantly increased coronary blood flow, conductance, and the balance between coronary flow and metabolism in obese swine (P < 0.05). These changes were associated with a ~50 % increase in inward CaV1.2 current and elevations in expression of the pore-forming subunit (α1c) of CaV1.2 channels in coronary smooth muscle cells from obese swine. Taken together, these findings indicate that electromechanical coupling between KV and CaV1.2 channels is involved in the regulation of coronary vasomotor tone and that increases in CaV1.2 channel activity contribute to coronary microvascular dysfunction in the setting of obesity.

Membrane biophysics and mechanics in Alzheimer's disease

Alzheimer's disease is a chronic neurodegenerative disorder characterized by neuronal loss, cerebrovascular inflammation, and accumulation of senile plaques in the brain parenchyma and cerebral blood vessels. Amyloid-beta peptide (Abeta), a major component of senile plaques, has been shown to exert multiple toxic effects to neurons, astrocytes, glial cells, and brain endothelium. Oligomeric Abeta can disturb the structure and function of cell membranes and alter membrane mechanical properties, such as membrane fluidity and molecular order. Much of these effects are attributed to their capability to trigger oxidative stress and inflammation. In this review, we discuss the effects of Abeta on neuronal cells, astrocytes, and cerebral endothelial cells with special emphasis on cell membrane properties and cell functions.

Rapid effects of 1alpha,25(OH)2D3 in resting human peripheral blood mononuclear cells

The steroid hormone 1alpha,25(OH)2D3 produces biological responses via both genomic and nongenomic mechanisms. Stimulation of rapid, nongenomic responses by 1alpha,25(OH)2D3 has been postulated to result from interaction of the ligand with cell membrane 1alpha,25(OH)2D3 receptors and to involve membrane receptors. We examined the rapid effects of 1alpha,25(OH)2D3 on calcium mobilization and calcium entry into resting human peripheral blood mononuclear cells isolated from healthy volunteers. We also investigated the possible involvement of purinergic receptors in this action. 1alpha,25(OH)2D3 induced a time-dependent increase in intracellular calcium concentration ([Ca2+]i). The initial 1alpha,25(OH)2D3-stimulated calcium increment was sensitive to thapsigargin (Tg), indicating its origins in calcium release from intracellular stores. 2-Aminoethyldiphenyl borate (2APB), an inhibitor of capacitative calcium entry, caused a significant [Ca2+]i decrease in human cells treated with 1alpha,25(OH)2D3. Furthermore, in contrast to observations in osteoblasts and skeletal muscle cells, nifedipine had no effect on 1alpha,25(OH)2D3-induced calcium entry, suggesting that L-type calcium channels were not implicated in this action. Besides, 1alpha,25(OH)(2)D3 prevented the calcium entry induced by 3'-O-(4-benzoyl)benzoyl-adenosine 5'-triphosphate (BzATP), a specific agonist of purinergic P2X7 receptors. This finding was further confirmed by 1alpha,25(OH)2D3-induced reduction of BzATP- and 4-aminopyridine (4AP)-stimulated ethidium bromide fluorescence. The presented results demonstrate, for the first time in healthy, resting human peripheral blood mononuclear cells that 1alpha,25(OH)2D3 is capable of exerting a rapid, nongenomic effect on [Ca2+]i, while inhibiting of the P2X7 channel permeability.

Multiple sclerosis – novel insights and new therapeutic strategies

PURPOSE OF REVIEW

This review focuses on novel aspects of the pathogenesis and advances in the therapy of multiple sclerosis (MS).

RECENT FINDINGS

Recent observations suggest that early lesion development in MS may start in some forms with oligodendrocyte death and that inflammation appears as a secondary phenomenon only. The lack of sufficient remyelination in MS may be the result of a disturbed function of basic helix-loop-helix transcription factors. Clinically the identification of patients with a clinically isolated syndrome at high risk to develop clinically definite MS remains difficult; the predictive value of serum antibodies against myelin proteins remains controversial. The role of neutralizing antibodies in interferon therapy is discussed. New therapeutic approaches in MS are emerging.

SUMMARY

The existing view on the pathogenesis of MS is still changing. The original assumption that cell-mediated demyelination is the key event in lesion development dictating clinical disability is critically reviewed and alternative pathways have been suggested. Oligodendrocyte death, axonal loss, the role of CD8 T lymphocytes, T regulatory cells, and B lymphocytes have come into the focus of newly evolving concepts in MS pathogenesis. A deepened understanding of the immunopathogenesis of this disease translates into innovative therapeutic approaches, such as blockade of alpha4 integrins by a humanized monoclonal antibody. In various animal models cell-replacement strategies yield promising results; however, turning these findings into an effective therapy in MS patients has a long way to go.

A polycystin-1 multiprotein complex is disrupted in polycystic kidney disease cells

Autosomal dominant polycystic kidney disease (ADPKD) is typified by the accumulation of fluid-filled cysts and abnormalities in renal epithelial cell function. The disease is principally caused by mutations in the gene encoding polycystin-1, a large basolateral plasma membrane protein expressed in kidney epithelial cells. Our studies reveal that, in normal kidney cells, polycystin-1 forms a complex with the adherens junction protein E-cadherin and its associated catenins, suggesting a role in cell adhesion or polarity. In primary cells from ADPKD patients, the polycystin-1/polycystin-2/E-cadherin/beta-catenin complex was disrupted and both polycystin-1 and E-cadherin were depleted from the plasma membrane as a result of the increased phosphorylation of polycystin-1. The loss of E-cadherin was compensated by the transcriptional upregulation of the normally mesenchymal N-cadherin. Increased cell surface N-cadherin in the disease cells in turn stabilized the continued plasma membrane localization of beta-catenin in the absence of E-cadherin. The results suggest that enhanced phosphorylation of polycystin-1 in ADPKD cells precipitates changes in its localization and its ability to form protein complexes that are critical for the stabilization of adherens junctions and the maintenance of a fully differentiated polarized renal epithelium.

4-Aminopyridine activates calcium influx through modulation of the pore-forming purinergic receptor in human peripheral blood mononuclear cells

We investigated whether 4-aminopyridine (4AP), a drug recently linked to calcium influx and apoptosis, also affected purinergic receptor channels that are known to play an important role in the activation of T lymphocytes. The application of 4AP induced a rise in [Ca2+]i that was sensitive to nickel. This action was also observed in cells in which calcium reserves were emptied using thapsigargin (Tg). However, it was not present in the absence of extracellular Ca2+, despite full internal reserves. Adenosine trisphosphate (ATP), a partial agonist and a physiological activator of purinergic receptors, also stimulated Ca2+ entry independently of the calcium release from internal compartments. The effects of 4AP and ATP were not additive when studied on the same population of cells. KN-62 inhibited an increase in calcium entry induced by 4AP, while brilliant blue G (BBG) prevented it, supporting the hypothesis that purinergic P2X7 receptors are involved in this action. Furthermore, 4AP allowed entry of ethidium bromide (314 Da) but not propidium iodide (415 Da) into the cell, also corroborating the involvement of P2X7 pores. The presented results demonstrate, for the first time in human mononuclear cells isolated from healthy volunteers, that the P2X7 channel pore is involved in the action of 4AP and intervenes in the sustained calcium entry induced in response to 4AP.Key words: calcium, human lymphocytes, 4-aminopyridine, purinergic receptors.