The time course of changes in cyclic nucleotide levels during cholinergic inhibition of positive inotropic actions of isoprenaline and theophylline in the isolated canine ventricular myocardium

1980 ◽  
Vol 312 (2) ◽  
pp. 175-182 ◽  
Author(s):  
Masao Endoh
Keyword(s):  
Cyclic Nucleotide ◽  
Time Course ◽  
Ventricular Myocardium ◽  
Canine Ventricular Myocardium

Demonstration of hysteresis in refractoriness of canine ventricular myocardium

1988 ◽  
Vol 255 (6) ◽  
pp. H1342-H1348
Author(s):  
C. Giorgi ◽  
M. Vermeulen ◽  
R. Cardinal ◽  
P. Savard ◽  
R. Nadeau ◽  
...  
Keyword(s):  
Pulse Width ◽  
Cycle Length ◽  
Ventricular Myocardium ◽  
Ventricular Muscle ◽  
Cycle Lengths ◽  
Long Pulse ◽  
Basic Cycle Length ◽  
Canine Ventricular Myocardium

The properties and determinants of hysteresis during ventricular effective refractory period (VERP) measurements by an extrastimulus technique were determined in 15 anesthetized open-chest dogs as well as in isolated ventricular muscle (n = 6). VERP was determined both by decreasing the S1-S2 interval and also by increasing S1S2. Hysteresis was then calculated by subtracting the VERP obtained with the decreasing S1S2 from the VERP obtained with the increasing S1S2. The effects of basic cycle length, pulse width, stimulation intensity, and the number of basic drives on VERP and hysteresis were evaluated. VERP was shorter for long pulse width, high stimulation intensities, and shorter basic cycle lengths. These modifications were not associated with significant changes of hysteresis. VERP was shorter during decreasing S1S2 than during increasing S1S2. Hysteresis was greater with 6 basic drive cycles than with 12 (P less than 0.001) in both in vivo and in vitro preparations. The data suggest that 1) hysteresis occurs during VERP measurements; 2) hysteresis is independent of stimulation modality; and 3) hysteresis decreases with the number of basic drive cycles.

scholarly journals Noncatalytic Inhibition of Cyclic Nucleotide–gated Channels by Tyrosine Kinase Induced by Genistein

1999 ◽  
Vol 113 (1) ◽  
pp. 45-56 ◽  
Author(s):  
Elena Molokanova ◽  
Alexei Savchenko ◽  
Richard H. Kramer
Keyword(s):  
Tyrosine Phosphorylation ◽  
Cyclic Nucleotide ◽  
Tyrosine Kinases ◽  
Time Course ◽  
Protein Tyrosine Phosphatases ◽  
Competitive Inhibitor ◽  
Rod Photoreceptor ◽  
Protein Tyrosine ◽  
Atp Binding Site ◽  
Cng Channel

Rod photoreceptor cyclic nucleotide–gated (CNG) channels are modulated by tyrosine phosphorylation. Rod CNG channels expressed in Xenopus oocytes are associated with constitutively active protein tyrosine kinases (PTKs) and protein tyrosine phosphatases that decrease and increase, respectively, the apparent affinity of the channels for cGMP. Here, we examine the effects of genistein, a competitive inhibitor of the ATP binding site, on PTKs. Like other PTK inhibitors (lavendustin A and erbstatin), cytoplasmic application of genistein prevents changes in the cGMP sensitivity that are attributable to tyrosine phosphorylation of the CNG channels. However, unlike these other inhibitors, genistein also slows the activation kinetics and reduces the maximal current through CNG channels at saturating cGMP. These effects occur in the absence of ATP, indicating that they do not involve inhibition of a phosphorylation event, but rather involve an allosteric effect of genistein on CNG channel gating. This could result from direct binding of genistein to the channel; however, the time course of inhibition is surprisingly slow (>30 s), raising the possibility that genistein exerts its effects indirectly. In support of this hypothesis, we find that ligands that selectively bind to PTKs without directly binding to the CNG channel can nonetheless decrease the effect of genistein. Thus, ATP and a nonhydrolyzable ATP derivative competitively inhibit the effect of genistein on the channel. Moreover, erbstatin, an inhibitor of PTKs, can noncompetitively inhibit the effect of genistein. Taken together, these results suggest that in addition to inhibiting tyrosine phosphorylation of the rod CNG channel catalyzed by PTKs, genistein triggers a noncatalytic interaction between the PTK and the channel that allosterically inhibits gating.

Ca2+ sensitizer Org-30029 reverses acidosis- and BDM-induced contractile depression in canine myocardium

1996 ◽  
Vol 271 (5) ◽  
pp. H1829-H1839 ◽  
Author(s):  
A. Watanabe ◽  
H. Tomoike ◽  
M. Endoh
Keyword(s):  
Direct Action ◽  
Ventricular Myocardium ◽  
Cross Bridge ◽  
Force Relation ◽  
Myocardial Contractile ◽  
Butanedione Monoxime ◽  
The Cross ◽  
Sensitizing Effect ◽  
Canine Myocardium ◽  
Canine Ventricular Myocardium

Effects of the Ca2+ sensitizer N-hydroxy-5,6-dimethoxy-benzo[b]thiophene-2-carboximidamide hydrochloride (Org-30029) on the myocardial contractile depression induced by acidosis and 2,3-butanedione monoxime (BDM) were investigated in aequorin-loaded canine ventricular myocardium. The peak Ca2+ transient-peak force relation during administration of Org-30029 (10(-4) to 10(-3) M) was shifted to the left and upward compared with the relation for elevation of the extracellular Ca2+ concentration ([Ca2+]o) (2.5-12.5 mM). Acidosis (pH 6.6) depressed the force with a small increase in the peak Ca2+ transient. BDM (3 mM) depressed the force with no change in the peak and duration of the Ca2+ transient, indicating that BDM may inhibit selectively the cross-bridge interaction. During acidosis or in the presence of BDM, elevation of [Ca2+]o increased the peak Ca2+ transient to the same extent as that in the control, but the force was inhibited. In contrast, Org-30029 increased the force to a level equivalent to the control with a slight change in the peak Ca2+ transient. In addition, during acidosis, Org-30029 (10(-3) M) increased the force in association with a slight decrease in the peak Ca2+ transient. Thus Org-30029 can reverse the myocardial contractile depression induced by a decrease in the Ca2+ sensitivity of myofilaments, as occurs in pathophysiological situations such as acidosis in cardiac ischemia. Org-30029 may exert the Ca(2+)-sensitizing effect by an increase in the affinity of troponin C for Ca2+ and by a direct action on the cross-bridge interaction.

scholarly journals Analysis of the contribution of Ito to repolarization in canine ventricular myocardium

2011 ◽  
Vol 164 (1) ◽  
pp. 93-105 ◽  
Author(s):  
L Virág ◽  
N Jost ◽  
R Papp ◽  
I Koncz ◽  
A Kristóf ◽  
...  
Keyword(s):  
Ventricular Myocardium ◽  
Canine Ventricular Myocardium

scholarly journals Telocytes express ANO ‐1‐encoded chloride channels in canine ventricular myocardium

2019 ◽  
Vol 35 (3) ◽  
pp. 515-521 ◽  
Author(s):  
Christopher V. DeSimone ◽  
Christopher J. McLeod ◽  
Pedro J. Gomez Pinilla ◽  
Arthur Beyder ◽  
Gianrico Farrugia ◽  
...  
Keyword(s):  
Chloride Channels ◽  
Ventricular Myocardium ◽  
Canine Ventricular Myocardium

Myocardial amino acid transport by canine sarcolemma vesicles

1987 ◽  
Vol 252 (6) ◽  
pp. H1070-H1076
Author(s):  
L. H. Young ◽  
B. L. Zaret ◽  
E. J. Barrett
Keyword(s):  
Amino Acid ◽  
Sarcoplasmic Reticulum ◽  
Membrane Vesicles ◽  
Amino Acid Uptake ◽  
Ventricular Myocardium ◽  
Transport Systems ◽  
Acid Uptake ◽  
Leucine Uptake ◽  
Alanine Transport ◽  
Canine Ventricular Myocardium

The transport of L-alanine and L-leucine into membrane vesicles isolated from mature canine ventricular myocardium was studied. Transport was assessed in purified sarcolemma and in vesicles differentially enriched either for sarcolemma or sarcoplasmic reticulum to further localize these transport systems. An imposed inward gradient of a NaNO3 stimulated uptake of L-alanine but not L-leucine by these vesicles. Amino acid uptake by these vesicles occurred into an osmotically active space. The stimulatory effect of Na+ on alanine transport was most striking in the purified sarcolemma vesicles, where Na+-stimulated alanine flux was 45 +/- 14 pmol X mg-1 X min-1. Furthermore, Na+-dependent alanine transport activity appeared to copurify with Na+-K+-ATPase activity, which served as a marker for sarcolemma membrane when these activities were compared in the three different membrane preparations. Leucine transport by sarcolemma was not altered by an imposed Na+ gradient. However, leucine uptake was a saturable function of extravesicular leucine and was inhibited by valine. In contrast, in sarcoplasmic reticulum membrane vesicles leucine uptake increased proportionately with increasing media leucine and was unaffected by valine. Our results demonstrate the feasibility of directly studying the transport of naturally occurring amino acids in membrane vesicles from mammalian heart, and the presence of Na+-dependent alanine transport system and a Na+-independent leucine transporter in the sarcolemma but not in sarcoplasmic reticulum of canine ventricular myocardium.

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