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K Ondrias

Publications and source records attributed to K Ondrias.

At least 19 recordsLinked to original sources
PubMed2005

IP3 type 1 receptors in the heart: their predominance in atrial walls with ganglion cells.

Previously we have shown that inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs) are abundantly expressed in the atria of rat hearts. Since arrangement of atria is very heterogeneous, in this work we focused on the precise localization of IP3 receptors in the left atrium, where the gene expression of the type 1 IP3R was the highest. The mRNA levels of the IP3 type 1 receptors in the left atrium, left ventricle and myocytes were determined using real-time polymerase chain reaction and Taqman probe. For precise localization, immunohistochemistry with the antibody against type 1 IP3Rs was performed. The mRNA of type 1 IP3 receptor was more than three times higher in the left atrium than in the left ventricle, as determined by real-time PCR. Expression of the type 1 IP3 receptor mRNA was higher in the atria, especially in parts containing cardiac ganglion cells. The atrial auricles, which are particularly free of ganglion cells, and the ventricles (wall of the right and left ventricle and ventricular septum) contained four to five times less IP3 receptors than atrial samples with ganglia. IP3R type 1 immunoreactivity detected by a confocal microscope attributed the most condensed signal on ganglionic cells, although light immunoreactivity was also seen in cardiomyocytes. These results show that type 1IP3 receptors predominate in intrinsic neuronal ganglia of cardiac atria.

Animals↗
PubMed2004

Quinine inhibits mitochondrial ATP-regulated potassium channel from bovine heart.

The mitochondrial ATP-regulated potassium (mitoK(ATP) channel has been suggested as trigger and effector in myocardial ischemic preconditioning. However, molecular and pharmacological properties of the mitoK(ATP) channel remain unclear. In the present study, single-channel activity was measured after reconstitution of the inner mitochondrial membrane from bovine ventricular myocardium into bilayer lipid membrane. After incorporation, a potassium-selective current was recorded with mean conductance of 103 +/- 9 pS in symmetrical 150 mM KCl. Single-channel activity of this reconstituted protein showed properties of the mitoK(ATP) channel: it was blocked by 500 microM ATP/Mg, activated by the potassium-channel opener diazoxide at 30 microM, inhibited by 50 microM glibenclamide or 150 microM 5-hydroxydecanoic acid, and was not affected by the plasma membrane ATP-regulated potassium-channel blocker HMR1098 at 100 microM. We observed that the mitoK(ATP) channel was blocked by quinine in the micromolar concentration range. The inhibition by quinine was additionally verified with the use of 86Rb+ flux experiments and submitochondrial particles. Quinine inhibited binding of the sulfonylurea derivative [3H]glibenclamide to the inner mitochondrial membrane. We conclude that quinine inhibits the cardiac mitoK(ATP) channel by acting on the mitochondrial sulfonylurea receptor.

Animals↗
PubMed2003

The inositol 1,4,5-trisphosphate receptor--transcriptional regulation and modulation by phosphorylation.

Inositol 1,4,5-trisphosphate receptors (IP3Rs) are intracellular membrane calcium channels essential for the release of calcium from intracellular stores. They form pathways for Ca2+ release that amplifies signals transmitted via plasma membrane receptors and so mediate a large array of calcium-regulated signal transduction events, from control of gene expression, through regulation of cell proliferation and other functions, to cell death. Molecular properties, expression and regulation of IP3Rs have been recently reviewed by others and thus these aspects will be mentioned only briefly in this article. This minireview will focus on the transcriptional regulation of IP3Rs and their modulation by phosphorylation.

Animals↗
PubMed2002

Distribution of neuronal and non-neuronal spliced variants of type 1 IP(3)-receptor in rat hypothalamus and brain stem.

In the nervous system, inositol 1,4,5-trisphosphate (IP(3)) is one of the second messengers produced by PI hydrolysis and triggers IP(3)-receptor (IP(3)R) mediated calcium release from intracellular pools. Throughout the brain, the type 1 IP(3)R is predominantly expressed and its mRNA is widely distributed. Alternative splicing of IP(3)R1 (SI and SII) occurs in two distinct regions. SI splicing in the middle of the ligand binding domain may alter the IP(3) binding activity, while SII splicing probably affects the protein kinase A phosphorylation sites and kinetics. Selective use of IP(3)-receptor subtypes may permit a tissue specific and developmentally specific expression of functionally distinct channels. The present work was focused on detection of the alternatively spliced mRNA of type 1 IP(3)-receptor in individual brain structures and nuclei. Using RT-PCR we detected neuronal (535bp) and non-neuronal (410bp) forms. We identified both spliced variants in the majority of brain structures, except in the cerebellum and medulla. In the cerebellum, the neuronal form of type 1 IP(3)R was found exclusively, while in the medulla, the non-neuronal form was much more abundant. Nevertheless, Western blot analysis and hybridization with specific antibody against IP(3)R revealed no qualitative, but only quantitative differences. Similarly, IP(3) dependent calcium release did not show any differences between the cerebellum and pons. These results demonstrate the distribution of alternatively spliced S2 variants of type 1 IP(3)R in selected brain structures and nuclei. The physiological relevance of these two forms remains to be elucidated by further studies.

Alternative Splicing↗
PubMed2002

Coupled gating between individual cardiac ryanodine calcium release channels.

In order to study interactions between ryanodine receptor calcium release (RyR2) channels during excitation-contraction coupling in cardiac muscle, we used bilayer lipid membrane (BLM) and improved the method of cardiac sarcoplasmic vesicle fusion into BLM. We increased fusion gradient for the vesicles, used chloride ions for fusion up to concentration of 1.2 mol/l and fused the vesicles by adding them directly to the forming BLM. Under these conditions, increased probability of fusion of vesicles containing 2-7 ryanodine channels into BLM was observed. Interestingly about 10% of the channels did not gate into BLM independently, but their gating was coupled. At 53 mmol/l calcium solution, two coupled gating channels had double conductance (191 +/- 15 pS) in comparison with the noncoupled channels (93 +/- 10 pS). Activities of the coupled channels were decreased by 5 micromol/l ryanodine and inhibited by 10 micromol/l ruthenium red similarly as single RyR2 channels. We suppose that cardiac sarcoplasmic vesicles contain single as well as coupled RyR2 channels.

Animals↗
PubMed2001

Coupled gating between cardiac calcium release channels (ryanodine receptors).

Excitation-contraction coupling in heart muscle requires the activation of Ca(2+)-release channels/type 2 ryanodine receptors (RyR2s) by Ca(2+) influx. RyR2s are arranged on the sarcoplasmic reticular membrane in closely packed arrays such that their large cytoplasmic domains contact one another. We now show that multiple RyR2s can be isolated under conditions such that they remain physically coupled to one another. When these coupled channels are examined in planar lipid bilayers, multiple channels exhibit simultaneous gating, termed "coupled gating." Removal of the regulatory subunit, the FK506 binding protein (FKBP12.6), functionally but not physically uncouples multiple RyR2 channels. Coupled gating between RyR2 channels may be an important regulatory mechanism in excitation-contraction coupling as well as in other signaling pathways involving intracellular Ca(2+) release.

Animals↗
PubMed2001

Effect of nicotinic acid adenine dinucleotide phosphate on ryanodine calcium release channel in heart.

Nicotinic acid adenine dinucleotide phosphate (NAADP), a molecule derived from nicotinamide adenine dinucleotide phosphate (NADP+), is a recently identified nucleotide that activates Ca2+ release from intracellular stores in invertebrate eggs and in mammalian cells. NAADP could function as an intracellular messenger for mobilizing internal Ca2+ stores, however the targets and nature of NAADP-induced Ca2+ release are unknown. We report here that NAADP (3-10 microM) induces Ca2+ release from rat heart microsomes and that NAADP (1-10 microM) activates single ryanodine receptor/calcium release channels (RyR2) from dog heart incorporated into bilayer lipid membranes. The results indicate that NAADP may play a role in cardiac excitation-contraction coupling by acting on RyR2 channels.

Animals↗
PubMed2001

Effect of ethanol on tracheal potassium channels reconstituted into bilayer lipid membranes.

We examined the effect of ethanol on single potassium channels derived from plasma membranes of bovine tracheal smooth muscles. The observed potassium channels had a conductance of 296 +/- 31 pS (mean +/- S.D.) in symmetrical 250 mmol/l KCl solutions, and exhibited a voltage- and Ca2+-dependence similar to BKCa channels. Ethanol at 50, 100 and 200 mM concentrations increased the probability of open potassium channels to 112 +/- 5, 127 +/- 7 and 121 +/- 13% (mean +/- S.E.M.), respectively. It is suggested that increased activity of the BKCa channels by ethanol hyperpolarizes the plasma membrane and thus may contribute to relaxation of tracheal smooth muscle.

Animals↗
PubMed2000

Identification of type 1 IP(3) receptors in the rat kidney and their modulation by immobilization stress.

Inositol 1,4,5-trisphosphate receptor (IP(3)-receptor) is a calcium channel, transporting calcium from intracellular stores to the cytoplasm. In kidney, IP(3)-receptors are involved in the signal transduction of various hormones. In our work we studied the effect of immobilization stress on the IP(3)-receptor's protein content in renal cortex and the medulla of normotensive and hypertensive rats. We detected both mRNA and type 1 IP(3)-receptor protein in medulla, but not in renal cortex. We found that this receptor was approximately twice as abundant in normotensive as in genetically hypertensive rat kidney. Immobilization stress decreased the amount of type 1 IP(3)-receptor in the renal medulla of normotensive rats approximately five times, while no effect due to single and/or repeated stress was observed in the renal medulla of spontaneously hypertensive rats. The results indicate that expression of type 1 IP(3)-receptor in renal medulla is modulated by hypertension and immobilization stress.

Alternative Splicing↗
PubMed1999

Properties of a new calcium-permeable single channel from tracheal microsomes.

After the incorporation of the tracheal microsomal membrane into bilayer lipid membrane (BLM), a new single channel permeable for calcium was observed. Using the BLM conditions, 53 mM Ca2+ in trans solution versus 200 nM Ca2+ in cis solution, the single calcium channel current at 0 mV was 1.4-2.1 pA and conductance was 62-75 pS. The channel Ca2+/K+ permeability ratio was 4.8. The open probability (P-open) was in the range of 0.7-0.97. The P-open, measured at -10 mV to +30 mV (trans-cis), was not voltage dependent. The channel was neither inhibited by 10-20 microM ruthenium red, a specific blocker of ryanodine calcium release channel, nor by 10-50 microM heparin, a specific blocker of IP3 receptor calcium release channel, and its activity was not influenced by addition of 0.1 mM MgATP. We suggest that the observed new channel is permeable for calcium, and it is neither identical with the known type 1 or 2 ryanodine calcium release channel, nor type 1 or 2 IP3 receptor calcium release channel.

Adenosine Triphosphate↗
PubMed1999

EPR spectroscopy of free radical intermediates of antiarrhythmic-antihypoxic drug stobadine, a pyridoindole derivative.

Mechanisms of antioxidant action of stobadine, a pyridoindole derivative with cardioprotective and antihypoxic properties, has been probed using EPR spectroscopy. Oxidation of stobadine by PbO2/tBuOOH in benzene results in the formation of nitroxide radical observable directly by EPR spectroscopy at room temperature, indicating conversion of indolic amino group to the corresponding nitroxide.

Anti-Arrhythmia Agents↗
PubMed1998

FKBP12 modulates gating of the ryanodine receptor/calcium release channel.

Excitation-contraction (EC) coupling in muscle requires the activation of intracellular calcium release channels (CRC). Four type 1 ryanodine receptor (RyR1) molecules form each tetrameric CRC. Each RyR1 contains a binding site for the FK506 binding protein (FKBP12), a cis-trans peptidyl-prolyl isomerase that is required for coordinated gating of the four RyR1 subunits comprising the channel. When FKBP12 is bound to RyR1, it stabilizes the four subunits that form each CRC. We propose that binding of one FKBP12 to each RyR1 lowers the energy of twisted-amide peptidyl-prolyl bonds and stabilizes RyR1 in a conformation that permits coordinated gating of the four RyR1 subunits.

Animals↗
PubMed1998

Coupled gating between individual skeletal muscle Ca2+ release channels (ryanodine receptors)

Excitation-contraction coupling in skeletal muscle requires the release of intracellular calcium ions (Ca2+) through ryanodine receptor (RyR1) channels in the sarcoplasmic reticulum. Half of the RyR1 channels are activated by voltage-dependent Ca2+ channels in the plasma membrane. In planar lipid bilayers, RyR1 channels exhibited simultaneous openings and closings, termed "coupled gating." Addition of the channel accessory protein FKBP12 induced coupled gating, and removal of FKBP12 uncoupled channels. Coupled gating provides a mechanism by which RyR1 channels that are not associated with voltage-dependent Ca2+ channels can be regulated.

Animals↗
PubMed1998

Characterization of the ryanodine receptor/channel of invertebrate muscle.

Electron-microscopic analysis was used to show that invertebrate muscle has feetlike structures on the sarcoplasmic reticulum (SR) displaying the typical four-subunit appearance of the calcium (Ca2+) release channel/ryanodine receptor (RyR) observed in vertebrate skeletal muscle (K. E. Loesser, L. Castellani, and C. Franzini-Armstrong. J. Muscle Res. Cell Motil. 13: 161-173, 1992). SR vesicles from invertebrate muscle exhibited specific ryanodine binding and single channel currents that were activated by Ca2+, caffeine, and ATP and inhibited by ruthenium red. The single channel conductance of this invertebrate RyR was lower than that of the vertebrate RyR (49 and 102 pS, respectively). Activation of lobster and scallop SR Ca2+ release channel, in response to cytoplasmic Ca2+ (1 nM-10 mM), reflected a bell-shaped curve, as is found with the mammalian RyR. In contrast to a previous report (J.-H. Seok, L. Xu, N. R. Kramarcy, R. Sealock, and G. Meissner, J. Biol. Chem. 267: 15893-15901, 1992), our results show that regulation of the invertebrate and vertebrate RyRs is quite similar and suggest remarkably similar paths in these diverse organisms.

Adenosine Triphosphate↗
PubMed1998

Antioxidant and pro-oxidant effects of epinephrine and isoprenaline on peroxidation of LDL and lipid liposomes.

Antioxidant or pro-oxidant properties of epinephrine (EPI) and isoprenaline (ISO) were studied in the absence and presence of Fe2+, Fe3+ and Cu2+ ions. EPI and ISO (>2 micromol/l) inhibited peroxidation of low density lipoprotein (LDL) induced by 2, 2'-azobis(2-amidino-propane) (AAPH). EPI had a similar inhibitory potency as ISO, but their potency was several times higher than the potency of alpha-tocopherol (alpha-TOC). When the LDL peroxidation was induced by 5 micromol/l CuSO4, EPI and ISO enhanced LDL peroxidation at low concentrations (10micromol/l) and decreased peroxidation at higher concentrations (30 micromol/l). The compounds had a similar tendency to inhibit the peroxidation of phosphatidylcholine liposomes. EPI (3-30 micromol/l) inhibited lipid peroxidation of phosphatidylcholine liposomes induced by 2 mmol/l of AAPH, but it was less effective and even increased the peroxidation, when the samples contained 2 mmol/l AAPH with 50 micromol/l FeSO4 or 2 mmol/l AAPH with 20 micromol/l FeCl3. Inhibition of lipid peroxidation by EPI was also observed when studying decreased oxygen consumption, when the peroxidation of linoleic acid was induced by lipoxidase. In conclusion, EPI and ISO reduced lipid peroxidation, but they exhibit pro-oxidant properties in the presence of Fe2+, Fe3+ or Cu2+ ions, depending on the catecholamine and ionic concentration.

Amidines↗
PubMed1997

Nafazatrom inhibits peroxidation of phosphatidylcholine liposomes, heart homogenate and low density lipoproteins.

In order to contribute to the understanding of the biological properties of nafazatrom, an antithrombotic agent (NAP), we studied its effects on peroxidation of low density lipoproteins (LDL), lipid liposomes, heart homopgenate, and its interaction with alpha-tocopherol radical. NAP decreased the FeSO4 and H202-induced peroxidation of phosphatidylcholine liposomes and heart homogenate, and it decreased peroxidation of LDL induced by CuSO4 or 2,2'-azobis(2-amidinopropane). The antioxidant effect of NAF was about 3 times less potent than that of alpha-tocopherol (alpha-TOC) in phosphatidylcholine liposomes, and NAF was about 2-4 times more efficient to decrease peroxidation of LDL than alpha-TOC. Possible interaction of NAF with alpha-tocopherol radical (alpha-TR) was studied by EPR spectroscopy. NAF decreased the concentration of alpha-TR, but it was about 100-times less efficient than vitamin C. This may indicate that NAF does not interfere with alpha-TR formation and/or reduction of alpha-TR in biological system. The obtained results may help the explanation of biological effects of NAF.

Animals↗