Search Results - (Author, Cooperation:A. Terzic)

2015-07-16

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Adenosine Triphosphate/metabolism ; Animals ; Cell Line ; DNA, Mitochondrial/*genetics ; Embryo, Mammalian/cytology ; Fibroblasts/cytology/metabolism/pathology ; Gene Expression Profiling ; Haplotypes/genetics ; Humans ; Induced Pluripotent Stem Cells/*metabolism ; Leigh Disease/genetics/metabolism/pathology ; Mice ; Mitochondria/*genetics/*metabolism/pathology ; Mitochondrial Diseases/*genetics/*metabolism/pathology ; Mitochondrial Encephalomyopathies/genetics/metabolism/pathology ; Mutation/genetics ; Nuclear Transfer Techniques ; Nucleotides/genetics ; Oxygen Consumption ; Polymorphism, Single Nucleotide/genetics ; Sequence Analysis, RNA ; Skin/cytology

2018-01-13

American Heart Association (AHA)

1942-325X

1942-3268

Medicine

Statements and Guidelines

1432-1912

Key words Inositol 1 ; 4 ; 5-trisphosphate ; Malignant hyperthermia ; Calcium ; Skeletal muscle ; Dantrolene ; Ca2+ microelectrode ; Nitrendipine

Springer Online Journal Archives 1860-2000

Medicine

Abstract Malignant hyperthermia (MH) is associated with abnormal regulation of intracellular calcium in skeletal muscle fibers. Besides a mutation in the ryanodine receptor gene, an increase in inositol, 1,4,5-trisphosphate (InsP3) levels could be a possible candidate for the abnormal regulation of intracellular calcium. However, the effect of InsP3 on [Ca2+]i in MH is not known. Microinjection of InsP3 increased intracellular Ca2+ in intact skeletal muscle from malignant hyperthermia susceptible swines (MHS) with a higher potency and efficacy than in muscles from nonsusceptible (MHN) swines. Omission of extracellular Ca2+ or incubation of muscle fibers with Ca2+ channel blockers did not modify the response to InsP3. However, dantrolene (50 μM) a known blocker of intracellular Ca2+ release, decreased resting intracellular Ca2+ concentration and prevented the InsP3-induced increase in intracellular Ca2+. This suggests (i) that MHS skeletal muscles exhibit a higher responsiveness to InsP3-induced release of Ca2+, which could implicate InsP3 in the pathophysiology of MH, and (ii) that the beneficial effect of dantrolene in MHS could be related to its ability to prevent the InsP3-induced release of Ca2+.

Electronic Resource

1432-1912

Key words ATP-sensitive K+ channel ; Diadenosine pentaphosphate ; Diadenosine polyphosphates ; Channel gating ; Heart ; Cardiomyocyte

Springer Online Journal Archives 1860-2000

Medicine

Abstract  In numerous studies the intracellular mononucleotide-dependent gating of ATP-sensitive K+ (KATP) channels has been demonstrated. However, it is not known whether dinucleotide polyphosphates, a family of endogenous compounds structurally-related to ATP, could also modulate this ion conductance. Therefore, in the present study we assessed the direct effect of diadenosine 5′,5″-P1,P5-pentaphosphate (Ap5A) on cardiac KATP channel activity using the inside-out configuration of the patch-clamp technique. Addition of Ap5A (50 μM) to the internal side of membrane patches, excised from guinea-pig ventricular cells, strongly inhibited KATP channel activity. The estimated NPO (where N is the number of channels in the patch and PO the open probability of each channel) was 4.16±0.50 in the absence and 0.85±0.30 in the presence of Ap5A (50 μM). This effect of Ap5A was partially reversible, and the NP0 was 2.26±0.60 after washout of Ap5A. Exposure of KATP channels to increasing concentrations of Ap5A revealed that the Ap5A-induced inhibition is concentration-dependent with the half-maximal effective concentration of 16 μM (Hill coefficient: 1.6). On the basis of these results, we conclude that Ap5A is a potent antagonist of the KATP channel activity. This represents a previously unrecognized property of Ap5A, as well as the discovery of a potentially novel endogenous ligand of myocardial KATP channels.

Electronic Resource

1432-1912

Inositol 1,4,5-trisphosphate ; Malignant hyperthermia ; Calcium ; Skeletal muscle ; Dantrolene ; Ca2+ microelectrode ; Nitrendipine

Springer Online Journal Archives 1860-2000

Medicine

Abstract Malignant hyperthermia (MH) is associated with abnormal regulation of intracellular calcium in skeletal muscle fibers. Besides a mutation in the ryanodine receptor gene, an increase in inositol, 1,4,5-trisphosphate (InsP3) levels could be a possible candidate for the abnormal regulation of intracellular calcium. However, the effect of InsP3 on [Ca2+]i in MH is not known. Microinjection of InsP3 increased intracellular Ca2+ in intact skeletal muscle from malignant hyperthermia susceptible swines (MHS) with a higher potency and efficacy than in muscles from nonsusceptible (MHN) swines. Omission of extracellular Ca2+ or incubation of muscle fibers with Ca2+ channel blockers did not modify the response to InsP3. However, dantrolene (50 μM) a known blocker of intracellular Ca2+ release, decreased resting intracellular Ca2+ concentration and prevented the InsP3-induced increase in intracellular Ca2+. This suggests (i) that MHS skeletal muscles exhibit a higher responsiveness to InsP3-induced release of Ca2+, which could implicate InsP3 in the pathophysiology of MH, and (ii) that the beneficial effect of dantrolene in MHS could be related to its ability to prevent the InsP3-induced release of Ca2+.

Electronic Resource

1432-2013

Rhabdomyolysis ; Skeletal Muscle ; Calcium ; Dantrolene

Springer Online Journal Archives 1860-2000

Medicine

Abstract Exertional rhabdomyolysis is a myopathy of unknown pathophysiology. We measured intracellular resting calcium concentration ([Ca2+]i) by means of Ca2+-selective microelectrodes in intercostal muscle fibers from horses suffering from rhabdomyolysis, and from horses with no evidence of neuromuscular disorder. [Ca2+]i was several-fold higher in muscle fibers from horses suffering from rhabdomyolysis when compared to controls. Treatment of rhabdomyolytic horses with dantrolene, an agent that prevents Ca2+ release from the sarcoplasmic reticulum, reduced [Ca2+]i toward control values, and accelerated the recovery from this myopathy. These results indicate that an acute episode of rhabdomyolysis is associated with elevation in [Ca2+]i in skeletal muscles, and that dantrolene might be of benefit in treating this disease.

Electronic Resource

1432-1424

Key words: KATP channels — Kinetic model — Inward rectifier K+ channel — ABC binding cassette — Pancreas — Cardiac

Springer Online Journal Archives 1860-2000

Biology

Chemistry and Pharmacology

Abstract. Co-expression of clones encoding Kir6.2, a K+ inward rectifier, and SUR1, a sulfonylurea receptor, reconstitutes elementary features of ATP-sensitive K+ (KATP) channels. However, the precise kinetic properties of Kir6.2/SUR1 clones remain unknown. Herein, intraburst kinetics of Kir6.2/SUR1 channel activity, heterologously co-expressed in COS cells, displayed mean closed times from 0.7 ± 0.1 to 0.4 ± 0.03 msec, and from 0.4 ± 0.1 to 2.0 ± 0.2 msec, and mean open times from 1.9 ± 0.4 to 4.5 ± 0.8 msec, and from 12.1 ± 2.4 to 5.0 ± 0.2 msec between −100 and −20 mV, and +20 to +80 mV, respectively. Burst duration for Kir6.2/SUR1 activity was 17.9 ± 1.8 msec with 5.6 ± 1.5 closings per burst. Burst kinetics of the Kir6.2/SUR1 activity could be fitted by a four-state kinetic model defining transitions between one open and three closed states with forward and backward rate constants of 1905 ± 77 and 322 ± 27 sec−1 for intraburst, 61.8 ± 6.6 and 23.9 ± 5.8 sec−1 for interburst, 12.4 ± 6.0 and 13.6 ± 2.9 sec−1 for intercluster events, respectively. Intraburst kinetic properties of Kir6.2/SUR1 clones were essentially indistinguishable from pancreatic or cardiac KATP channel phenotypes, indicating that intraburst kinetics per se were insufficient to classify recombinant Kir6.2/SUR1 amongst native KATP channels. Yet, burst kinetic behavior of Kir6.2/SUR1 although similar to pancreatic, was different from that of cardiac KATP channels. Thus, expression of Kir6.2/SUR1 proteins away from the pancreatic micro-environment, confers the burst kinetic identity of pancreatic, but not cardiac KATP channels. This study reports the kinetic properties of Kir6.2/SUR1 clones which could serve in the further characterization of novel KATP channel clones.

Electronic Resource

1432-1424

Key words: ATP-sensitive K+ channels — Uncoupler of oxidative phosphorylation — Protonophore — pH — Cardiac — DNP

Springer Online Journal Archives 1860-2000

Biology

Chemistry and Pharmacology

Abstract. Opening of ATP-sensitive K+ (KATP) channels by the uncoupler of oxidative phosphorylation, 2,4 dinitrophenol (DNP), has been assumed to be secondary to metabolic inhibition and reduced intracellular ATP levels. Herein, we present data which show that DNP (200 μm) can induce opening of cardiac KATP channels, under whole-cell and inside-out conditions, despite millimolar concentrations of ATP (1–2.5 mm). DNP-induced currents had a single channel conductance (71 pS), inward rectification, reversal potential, and intraburst kinetic properties (open time constant, τopen: 4.8 msec; fast closed time constant, τclosed(f): 0.33 msec) characteristic of KATP channels suggesting that DNP did not affect the pore region of the channel, but may have altered the functional coupling of the ATP-dependent channel gating. A DNP analogue, with the pH-titrable hydroxyl replaced by a methyl group, could not open KATP channels. The pH-dependence of the effect of DNP on channel opening under whole-cell, cell-attached, and inside-out conditions suggested that transfer of protonated DNP across the sarcolemma is essential for activation of KATP channels in the presence of ATP. We conclude that the use of DNP for metabolic stress-induced KATP channel opening should be reevaluated.

Electronic Resource