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M Thapsigargin (m + thapsigargin)

Distribution by Scientific Domains

Medical Sciences	75%

Selected Abstracts

Nonylphenol-induced cytosolic Ca2+ elevation and death in renal tubular cells

DRUG DEVELOPMENT RESEARCH, Issue 5 2009
Jeng-Yu Tsai
Abstract Nonylphenol is an environmental endocrine disrupter. The effect of nonylphenol on intracellular free Ca2+ levels ([Ca2+]i) and viability in Madin-Darby canine kidney (MDCK) cells was explored. Nonylphenol increased [Ca2+]i in a concentration-dependent manner (EC50,0.8,,M). Nonylphenol-induced Mn2+ entry demonstrated Ca2+ influx and removal of extracellular Ca2+ partly decreased the [Ca2+]i rise. The [Ca2+]i rise was inhibited by the protein kinase C activator, phorbol 13-myristate acetate (PMA) but not by L-type Ca2+ channel blockers. In Ca2+ -free medium, nonylphenol-induced [Ca2+]i rise was partly inhibited by pretreatment with 1,,M thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor). Conversely, nonylphenol pretreatment abolished thapsigargin-induced Ca2+ release. Nonylphenol-induced Ca2+ release was unaltered by inhibition of phospholipase C. At concentrations of 5,100,,M, nonylphenol killed cells in a concentration-dependent manner. The cytotoxic effect of 100,,M nonylphenol was not affected by preventing [Ca2+]i rises with BAPTA/AM. Collectively, this study shows that nonylphenol induced [Ca2+]i increase in MDCK cells via evoking Ca2+ entry through protein kinase C-regulated Ca2+ channels, and releasing Ca2+ from endoplasmic reticulum and other stores in a phospholipase C-independent manner. Nonylphenol also killed cells in a Ca2+ -independent fashion. Drug Dev Res, 2009. © 2009 Wiley-Liss, Inc. [source]

Melatonin Counteracts Alterations in Oxidative Metabolism and Cell Viability Induced by Intracellular Calcium Overload in Human Leucocytes: Changes with Age

BASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 1 2010
Javier Espino
In fact, the free radical theory of ageing proposes that deleterious actions of free radicals are responsible for the functional deterioration associated with ageing. Moreover, a close relationship exists between calcium homeostasis and oxidative stress. The current work was aimed at proving that intracellular calcium overload induced by N -formyl-methionyl-leucyl-phenylalanine (FMLP) and/or thapsigargin leads to oxidative stress. We additionally examined the effect of melatonin on the levels of reactive oxygen species (ROS) and cell viability in human leucocytes collected from young (20,30-year-old) and elderly (65,75-year-old) individuals under both basal and oxidative stress-induced conditions. Treatments with 10 nM FMLP and/or 1 ,M thapsigargin induced a transient increase in cytosolic free-calcium concentration ([Ca2 + ]c) in human leucocytes due to calcium release from internal stores, and led in turn to oxidative stress, as assessed by intracellular ROS measurement. Non-treated leucocytes from aged individuals exhibited higher ROS levels and lower rates of cell survival when compared to leucocytes from young individuals. Similar results were obtained in FMLP and/or thapsigargin-treated leucocytes from elderly individuals when compared to those from the young individuals. Melatonin treatment significantly reduced both hydrogen peroxide (H2O2) and superoxide anion levels, likely due to its free-radical scavenging properties, and enhanced leucocyte viability in both age groups. Therefore, melatonin may be a useful tool for the treatment of disease states and processes where an excessive production of oxidative damage occurs. [source]

4-Aminopyridine affects rat arterial smooth muscle BKCa currents by changing intracellular pH

BRITISH JOURNAL OF PHARMACOLOGY, Issue 8 2000
Polina Petkova-Kirova
The hypothesis whether or not 4-AP can affect vascular smooth muscle BKCa currents was tested using the patch-clamp technique, pH- and calcium-fluorimetry, and freshly isolated rat arterial smooth muscle cells. Application of 4-AP reversibly inhibited BKCa currents at an intracellular calcium ([Ca]i) of 250 nM with a half-block of 2.5 mM at +50 mV. The presence of 2 ,M thapsigargin, 10 ,M heparin, and 10 ,M ryanodine did not alter the effect of 4-AP on BKCa currents at [Ca]i 250 nM. At [Ca]i<100 nM 4-AP did not inhibit BKCa currents. Application of 4-AP to the intracellular or extracellular side of excised BKCa channels did not alter channel activity or channel amplitude. Replacement of the pH-sensitive calcium buffer EGTA by the pH-insensitive calcium buffer BAPTA in the intracellular solution turned the 4-AP-induced inhibition of BKCa currents into a stimulation at [Ca]i 250 nM. Application of 4-AP to single cells increased intracellular pH, which was accompanied by a reduction of [Ca]i in EGTA-loaded cells and a stable [Ca]i in BAPTA-loaded cells. Thus, these results suggest that in isolated vascular smooth muscle cells at [Ca]i>100 nM 4-AP affects BKCa currents via an alteration of intracellular pH. British Journal of Pharmacology (2000) 131, 1643,1650; doi:10.1038/sj.bjp.0703742 [source]

Regulation of junctional and non-junctional sarcoplasmic reticulum calcium release in excitation-contraction coupling in cat atrial myocytes

THE JOURNAL OF PHYSIOLOGY, Issue 1 2003
Katherine A. Sheehan
We have characterized the dependence on membrane potential (Vm) and calcium current (ICa) of calcium-induced calcium release (CICR) from the junctional-SR (j-SR, in the subsarcolemmal (SS) space) and non-junctional-SR (nj-SR, in the central (CT) region of the cell) of cat atrial myocytes using whole-cell voltage-clamp together with spatially resolved laser-scanning confocal microscopy. Subsarcolemmal and central [Ca2+]i transient amplitudes and ICa had a bell-shaped dependence on Vm, but [Ca2+]i reached a maximum at more negative Vm (-10 to 0 mV) than ICa (+10 mV). Termination of ICa after a brief depolarization (2.5 to 22.5 ms) immediately interrupted only the SS [Ca2+]i transient, leaving the development of the CT [Ca2+]i transient unaffected. Block of SR function with 20 ,m ryanodine and 2 ,m thapsigargin, revealed that > 90 % of the control [Ca2+]i transient amplitude was attributable to active SR Ca2+ release through ryanodine receptors (RyRs). The gain of SR Ca2+ release was highest in the SS space at negative test potentials and was less pronounced in the CT region. Inhibition of Na+ -Ca2+ exchange resulted in prolonged and higher amplitude [Ca2+]i transients, elevated resting [Ca2+]i, accelerated propagation of CICR, decreased extrusion of Ca2+ and an increase in j-SR Ca2+ load. Increasing the cytosolic Ca2+ buffer capacity by internal perfusion with 1 mm EGTA limited SR Ca2+ release to the SS region, indicating that Ca2+ release from nj-SR is initiated by diffusion of Ca2+ from the cell periphery and propagating CICR. Junctional-SR Ca2+ release occurred at discrete sites whose order of activation and amplitude of release varied from beat to beat. In conclusion, during normal excitation-contraction coupling in cat atrial myocytes, only Ca2+ release from the j-SR is directly activated by Ca2+ entering via ICa. Elevation of SS [Ca2+]i is required to provide the cytosolic Ca2+ gradient needed to initiate regenerative and propagating CICR from nj-SR. [source]