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Angiotensin II Type 1 Receptor-Mediated Electrical Remodeling in Mouse Cardiac Myocytes.

Kim J, Gao J, Cohen IS, Mathias RT - PLoS ONE (2015)

Bottom Line: Pre-application of the microtubule destabilizing agent colchicine eliminated A2 effects on Ito and AP duration, suggesting these effects depend on intracellular trafficking.Application of the biased agonist SII ([Sar1-Ile4-Ile8]A2), which stimulates receptor internalization without G protein activation, caused Ito reduction and AP prolongation similar to A2-induced changes.Moreover, all measured properties parallel those measured in dog heart, suggesting an autocrine RAS may be a fundamental feedback system that is present across species.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology & Biophysics, State University of New York at Stony Brook, Stony Brook, New York, United States of America.

ABSTRACT
We recently characterized an autocrine renin angiotensin system (RAS) in canine heart. Activation of Angiotensin II Type 1 Receptors (AT1Rs) induced electrical remodeling, including inhibition of the transient outward potassium current Ito, prolongation of the action potential (AP), increased calcium entry and increased contractility. Electrical properties of the mouse heart are very different from those of dog heart, but if a similar system existed in mouse, it could be uniquely studied through genetic manipulations. To investigate the presence of a RAS in mouse, we measured APs and Ito in isolated myocytes. Application of angiotensin II (A2) for 2 or more hours reduced Ito magnitude, without affecting voltage dependence, and prolonged APs in a dose-dependent manner. Based on dose-inhibition curves, the fast and slow components of Ito (Ito,fast and IK,slow) appeared to be coherently regulated by [A2], with 50% inhibition at an A2 concentration of about 400 nM. This very high K0.5 is inconsistent with systemic A2 effects, but is consistent with an autocrine RAS in mouse heart. Pre-application of the microtubule destabilizing agent colchicine eliminated A2 effects on Ito and AP duration, suggesting these effects depend on intracellular trafficking. Application of the biased agonist SII ([Sar1-Ile4-Ile8]A2), which stimulates receptor internalization without G protein activation, caused Ito reduction and AP prolongation similar to A2-induced changes. These data demonstrate AT1R mediated regulation of Ito in mouse heart. Moreover, all measured properties parallel those measured in dog heart, suggesting an autocrine RAS may be a fundamental feedback system that is present across species.

No MeSH data available.


Related in: MedlinePlus

A2-mediated dose-inhibition relationships for Ito,fast and IK,slow.Percent inhibitions induced by various A2 concentrations (0.05 to 10 μM) were calculated from peak Ito,fast and IK,slow values obtained at Vtest = +50 mV (Table 1). Percent inhibition vs. [A2] relationships of Ito,fast(A) and IK,slow(B) were plotted and standard binding curves were fit to the data. Based on the curve fits, half-maximal reductions of Ito,fast and IK,slow correspond to A2 concentrations of 400 nM and 368 nM respectively, and 90%-maximal reductions correspond to 1643 nM and 1462 nM respectively, as indicated in the graphs. Based on the analysis, stimulation with high [A2] can maximally inhibit Ito,fast by 41% and IK,slow by 47%.
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pone.0138711.g004: A2-mediated dose-inhibition relationships for Ito,fast and IK,slow.Percent inhibitions induced by various A2 concentrations (0.05 to 10 μM) were calculated from peak Ito,fast and IK,slow values obtained at Vtest = +50 mV (Table 1). Percent inhibition vs. [A2] relationships of Ito,fast(A) and IK,slow(B) were plotted and standard binding curves were fit to the data. Based on the curve fits, half-maximal reductions of Ito,fast and IK,slow correspond to A2 concentrations of 400 nM and 368 nM respectively, and 90%-maximal reductions correspond to 1643 nM and 1462 nM respectively, as indicated in the graphs. Based on the analysis, stimulation with high [A2] can maximally inhibit Ito,fast by 41% and IK,slow by 47%.

Mentions: Relative changes (%) in peak Ito,fast and IK,slow at Vtest = +50 mV were plotted as a function of [A2], and sigmoidal dose-inhibition curves were fit to the data as shown in Fig 4. The dose-inhibition relationships imply that in cells stimulated with saturating [A2], peak Ito,fast and IK,slow densities are attenuated by 41% and 47%, respectively. Additionally, the half maximal inhibitory concentrations (K0.5) of A2 for Ito,fast (400 nM) and IK,slow (368 nM) are similar and may be identical given experimental variability. Likewise, the 90%-maximal inhibitory concentrations (IC90) were also similar (Ito,fast: 1600 nM, IK,slow: 1500 nM). These findings suggest A2 stimulation coherently attenuates Ito,fast and IK,slow in a dose dependent manner. Thus the mechanisms underlying regulation of these two currents are similar, if not the same.


Angiotensin II Type 1 Receptor-Mediated Electrical Remodeling in Mouse Cardiac Myocytes.

Kim J, Gao J, Cohen IS, Mathias RT - PLoS ONE (2015)

A2-mediated dose-inhibition relationships for Ito,fast and IK,slow.Percent inhibitions induced by various A2 concentrations (0.05 to 10 μM) were calculated from peak Ito,fast and IK,slow values obtained at Vtest = +50 mV (Table 1). Percent inhibition vs. [A2] relationships of Ito,fast(A) and IK,slow(B) were plotted and standard binding curves were fit to the data. Based on the curve fits, half-maximal reductions of Ito,fast and IK,slow correspond to A2 concentrations of 400 nM and 368 nM respectively, and 90%-maximal reductions correspond to 1643 nM and 1462 nM respectively, as indicated in the graphs. Based on the analysis, stimulation with high [A2] can maximally inhibit Ito,fast by 41% and IK,slow by 47%.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4591968&req=5

pone.0138711.g004: A2-mediated dose-inhibition relationships for Ito,fast and IK,slow.Percent inhibitions induced by various A2 concentrations (0.05 to 10 μM) were calculated from peak Ito,fast and IK,slow values obtained at Vtest = +50 mV (Table 1). Percent inhibition vs. [A2] relationships of Ito,fast(A) and IK,slow(B) were plotted and standard binding curves were fit to the data. Based on the curve fits, half-maximal reductions of Ito,fast and IK,slow correspond to A2 concentrations of 400 nM and 368 nM respectively, and 90%-maximal reductions correspond to 1643 nM and 1462 nM respectively, as indicated in the graphs. Based on the analysis, stimulation with high [A2] can maximally inhibit Ito,fast by 41% and IK,slow by 47%.
Mentions: Relative changes (%) in peak Ito,fast and IK,slow at Vtest = +50 mV were plotted as a function of [A2], and sigmoidal dose-inhibition curves were fit to the data as shown in Fig 4. The dose-inhibition relationships imply that in cells stimulated with saturating [A2], peak Ito,fast and IK,slow densities are attenuated by 41% and 47%, respectively. Additionally, the half maximal inhibitory concentrations (K0.5) of A2 for Ito,fast (400 nM) and IK,slow (368 nM) are similar and may be identical given experimental variability. Likewise, the 90%-maximal inhibitory concentrations (IC90) were also similar (Ito,fast: 1600 nM, IK,slow: 1500 nM). These findings suggest A2 stimulation coherently attenuates Ito,fast and IK,slow in a dose dependent manner. Thus the mechanisms underlying regulation of these two currents are similar, if not the same.

Bottom Line: Pre-application of the microtubule destabilizing agent colchicine eliminated A2 effects on Ito and AP duration, suggesting these effects depend on intracellular trafficking.Application of the biased agonist SII ([Sar1-Ile4-Ile8]A2), which stimulates receptor internalization without G protein activation, caused Ito reduction and AP prolongation similar to A2-induced changes.Moreover, all measured properties parallel those measured in dog heart, suggesting an autocrine RAS may be a fundamental feedback system that is present across species.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology & Biophysics, State University of New York at Stony Brook, Stony Brook, New York, United States of America.

ABSTRACT
We recently characterized an autocrine renin angiotensin system (RAS) in canine heart. Activation of Angiotensin II Type 1 Receptors (AT1Rs) induced electrical remodeling, including inhibition of the transient outward potassium current Ito, prolongation of the action potential (AP), increased calcium entry and increased contractility. Electrical properties of the mouse heart are very different from those of dog heart, but if a similar system existed in mouse, it could be uniquely studied through genetic manipulations. To investigate the presence of a RAS in mouse, we measured APs and Ito in isolated myocytes. Application of angiotensin II (A2) for 2 or more hours reduced Ito magnitude, without affecting voltage dependence, and prolonged APs in a dose-dependent manner. Based on dose-inhibition curves, the fast and slow components of Ito (Ito,fast and IK,slow) appeared to be coherently regulated by [A2], with 50% inhibition at an A2 concentration of about 400 nM. This very high K0.5 is inconsistent with systemic A2 effects, but is consistent with an autocrine RAS in mouse heart. Pre-application of the microtubule destabilizing agent colchicine eliminated A2 effects on Ito and AP duration, suggesting these effects depend on intracellular trafficking. Application of the biased agonist SII ([Sar1-Ile4-Ile8]A2), which stimulates receptor internalization without G protein activation, caused Ito reduction and AP prolongation similar to A2-induced changes. These data demonstrate AT1R mediated regulation of Ito in mouse heart. Moreover, all measured properties parallel those measured in dog heart, suggesting an autocrine RAS may be a fundamental feedback system that is present across species.

No MeSH data available.


Related in: MedlinePlus