Biomedical subjects

Hristo Gagov

Publications and source records attributed to Hristo Gagov.

3 recordsLinked to original sources

PubMed2006

Urocortin-induced decrease in Ca2+ sensitivity of contraction in mouse tail arteries is attributable to cAMP-dependent dephosphorylation of MYPT1 and activation of myosin light chain phosphatase.

Urocortin, a vasodilatory peptide related to corticotropin-releasing factor, may be an endogenous regulator of blood pressure. In vitro, rat tail arteries are relaxed by urocortin by a cAMP-mediated decrease in myofilament Ca2+ sensitivity through a still unclear mechanism. Here we show that contraction of intact mouse tail arteries induced with 42 mmol/L KCl or 0.5 micromol/L noradrenaline was associated with a approximately 2-fold increase in the phosphorylation of the regulatory subunit of myosin phosphatase (SMPP-1M), MYPT1, at Thr696, which was reversed in arteries relaxed with urocortin. Submaximally (pCa 6.1) contracted mouse tail arteries permeabilized with alpha-toxin were relaxed with urocortin by 39+/-3% at constant [Ca2+], which was associated with a decrease in myosin light chain (MLC20Ser19), MYPT1Thr696, and MYPT1Thr850 phosphorylation by 60%, 28%, and 52%, respectively. The Rho-associated kinase (ROK) inhibitor Y-27632 decreased MYPT1 phosphorylation by a similar extent. Inhibition of PP-2A with 3 nmol/L okadaic acid had no effect on MYPT1 phosphorylation, whereas inhibition of PP-1 with 3 micromol/L okadaic acid prevented dephosphorylation. Urocortin increased the rate of dephosphorylation of MLC20Ser19 approximately 2.2-fold but had no effect on the rate of contraction under conditions of, respectively, inhibited kinase and phosphatase activities. The effect of urocortin on MLC20Ser19 and MYPT1 phosphorylation was blocked by Rp-8-CPT-cAMPS and mimicked by Sp-5,6-DCl-cBIMPS. In summary, these results provide evidence that Ca(2+)-independent relaxation by urocortin can be attributed to a cAMP-mediated increased activity of SMPP-1M which at least in part is attributable to a decrease in the inhibitory phosphorylation of MYPT1.

Animals↗

PubMed2004

Calcium-dependent changes in potassium currents in guinea-pig coronary artery smooth muscle cells after acute cobalt loading in vivo.

The aim of the present study was to determine whether cobalt poisoning induces haem oxidase isoenzyme-1 (HO-1) in coronary artery smooth muscle, or accounts for any changes in coronary smooth muscle cell (SMCs) membrane ionic currents that could result from this type of heavy metal poisoning. In SMCs isolated from cobalt-treated guinea-pig coronaries, K+ channel currents (IK) were much smaller than those in cells isolated from non-treated animals. Haemin (HO substrate) increased IK concentration dependently. This effect was mimicked by 1% CO and was abolished by pretreatment of cells with a competitive HO inhibitor, by inhibitors of guanylyl cyclase, protein kinase G or phospholipase C, as well as by blocking inositol trisphosphate-dependent Ca release, or sarcoplasmic reticulum Ca-ATPase, or by bathing cells in Ca-free external solution. Expression of the Na/Ca exchanger-1 (NCX-1) protein was reduced substantially in SMCs from coronary arteries of cobalt-treated animals. No expression of HO-1 was detected. It is concluded that acute cobalt poisoning in vivo depresses Ca-sensitive K currents via CO-dependent modulation of intracellular calcium availability, most probably by suppressing the expression of NCX-1 protein.

Animals↗

PubMed2003

Role of constitutively expressed heme oxygenase-2 in the regulation of guinea pig coronary artery tone.

Carbon monoxide (CO) is well known as a relaxing substance in the vasculature, where it is released during the heme oxygenase (HO) reaction. Little is known about the tissue-specific targets of CO in smooth muscles. To date the functional role of CO in the coronary artery remains unclear. The expression of HO-2, the constitutive isoform of HO, but not of HO-1 (inducible HO isoform) was demonstrated by immunohistochemical reaction. Contractile studies, performed under isometrical conditions, showed that CO, as well as hemin (given as a substrate for HO), relax de-endothelized coronary smooth muscle after the blockade of neuronal transmission. The action of hemin was antagonized by preliminary treatment of the vessel with SnPPIX--a competitive inhibitor of HO. The relaxatory effects of hemin were abolished in the presence of guanylyl-cyclase or protein kinase G antagonists. Patch-clamp studies revealed that hemin caused activation of iberiotoxin-blockable K outward current (I(K)) via guanylyl-cyclase and protein-kinase-G-dependent mechanisms. This activation coincided with hyperpolarization of the plasma membrane of single coronary smooth muscle cells by 8+/-3 mV, which was prevented by preliminary exposure of cells to 10 microM SnPPIX. The I(K)-augmenting effect of hemin was not affected by pretreatment of cells with cyclopiazonic acid and/or ryanodine, blockers of phospholipase C or heparin (applied via pipette), but was not observed when ATP was omitted from the dialyzing solution, or in the presence of Na-free, ATP-containing pipette solution. The omission of Ca(2+) from the bath or the replacement of Na with Li in both pipette and bath media also prevented the I(K)-activating effect of hemin. These results suggest that the constitutive HO-2 in coronary artery smooth muscle cells plays role in the modulation of tone. At the level of smooth muscle cells CO and its precursor hemin may cause hyperpolarization of the plasma membrane by activation of iberiotoxin-sensitive I(K) presumably via PKG-dependent activation of the Na/Ca exchanger. This activation is thought to increase the submembrane Ca(2+) concentration in the vicinity of large-conductance, Ca(2+)-sensitive K channels, thus causing voltage-dependent inhibition of Ca(2+) entry and subsequent relaxation of the vessel.

Adenosine Triphosphate↗