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Stretch-Dependent Release of Positively Inotropic Factors in Isolated Perfused Rat Hearts
RVSP (mmHg) PH
56.0 ± 21.5
Non−PH
30.0 ± 5.2
p
0.002
RVDP (mmHg)
RV EDP (mmHg)
CSANZ 2013 Abstracts
dP/dt min (mmHg/s)
dP/dt max (mmHg/s)
RV tau (ms)
IVRT (ms)
5.1 ± 6.6
11.0 ± 6.3 −530 ± 219
521 ± 209
53 ± 32
52 ± 25
−0.1 ± 3.3
3.8 ± 3.7 −304 ± 78
436 ± 146
31 ± 13
38 ± 16
0.03
0.004
0.006
0.27
0.04
0.13
S59
142 Studies of a Mouse Model of Cardiac ␣1A -Adrenergic Receptor Overexpression Provide Evidence For a Critical Role of RhoA/ROCK Signalling in Cardiac Contractility
Conclusion: Pulmonary hypertension is associated with abnormal measures of RV active relaxation and increased RVEDP.
Z. Yu 1,2,3,∗ , J. Tan 1 , A. McMahon 1,2,4 , S. Iismaa 1,3 , X. Xiao 1 , S. Kesteven 1 , M. Reichelt 1,5 , M. Mohl 1 , Y. Dai 1 , A. Sketchley 1 , L. Yang 1 , H. Gong 1 , D. Fatkin 1,2,3 , D. Allen 6 , S. Head 7 , R. Graham 1,2,3 , M. Feneley 1,2,3
http://dx.doi.org/10.1016/j.hlc.2013.05.141
Chang Cardiac Research Institute, Sydney, Australia Department, St Vincent’s Hospital, Sydney, Australia 3 Faculty of Medicine, University of New South Wales, Sydney, Australia 4 ANZAC Research Institute, Sydney, Australia 5 Physiology Department, University of Melbourne, Melbourne, Australia 6 Physiology Department, University of Sydney, Sydney, Australia 7 Physiology Department, University of New South Wales, Sydney, Australia
141 Stretch-Dependent Release of Positively Inotropic Factors in Isolated Perfused Rat Hearts M. Ward ∗ , X. Shen University of Auckland, New Zealand Background: Stretching cardiac muscle gives rise to a biphasic increase in contractility, with the secondary phase accompanied by an increase in the Ca2+ transients (the ‘slow force response’ or SFR). The mechanism that leads to the SFR is still debated. One theory suggests that stretch releases angiotensin II, activating the Na+ –H+ -exchanger, increasing [Na+ ]i and, subsequently, increasing Ca2+ entry by the Na+ /Ca2+ -exchanger. Our aim was to investigate the stretch-dependent release of extra-humoral factors which might mediate the SFR. Methods: Isolated Langendorff-perfused rat hearts were subjected to stretch by increasing the volume of a fluid-filled balloon in the LV. The coronary effluent from stretched and un-stretched hearts was collected via a cannula inserted into the RV and used to superfuse ventricular trabeculae at 2.1 m sarcomere length while measuring [Ca2+ ]i and twitch force. Samples of coronary effluent were also analysed using Liquid Chromatography/Mass Spectroscopy (LC/MS). Results: In trabeculae, the effluent from stretched hearts increased twitch force by 25% (p < 0.01, n = 12) and the [Ca2+ ]i transients by 11.5% (p < 0.05, n = 5), similar to that observed during the SFR. LC/MS analysis revealed an increase in fatty acid related metabolites such as arachidonic acid (AA) and prostaglandins (PG) in the stretched effluent. Both AA and PGF2␣ increased force and [Ca2+ ]i in trabeculae, and the COX inhibitor indomethacin reduced the SFR. Conclusions: Our study confirms that positively inotropic factors are released by stretch that could mediate the SFR, implicating a stretch-dependent signalling pathway downstream of COX. http://dx.doi.org/10.1016/j.hlc.2013.05.142
1 Victor
2 Cardiology
Despite evidence implicating the ␣1A -adrenergic receptor (AR) in the development of cardiac hypertrophy, we have previously reported that transgenic (TG) mice with cardiac-restricted ␣1A -AR overexpression (170-fold) exhibit enhanced ventricular contractility but not hypertrophy in vivo. The present study investigated the role of ␣1A -AR in cardiac contractility. We observed dose-related hypercontractile responses to the ␣1A -AR agonist, A61603, in isolated ␣1A -TG vs non-transgenic littermate (NTL) hearts and cardiomyocytes, which was due to an increased amplitude of the systolic rise in [Ca2+ ]i . In the absence of agonist stimulation, however, isolated ␣1A -TG hearts and cardiomyocytes exhibited reduced contractility despite unchanged [Ca2+ ]i . This basal hypocontractility was associated with decreased RhoA/Rho kinase (ROCK) activity and hypophosphorylation of both myosin phosphatase targeting subunit 1 (MYPT1) and cardiac myosin light chain 2 (cMLC2), all of which were rapidly reversed by the selective ␣1A -AR antagonist, RS100329. We also found that basal contractility in ␣1A -TG and NTL hearts was strongly correlated with RhoA activity and with phospho-MTPY1 and cMLC2 levels. Further, in isolated NTL hearts, inhibition of ROCK with a selective inhibitor, Y-27632, caused a rapid reduction in basal contractility, which phenocopied the basal hypocontractility observed in isolated untreated ␣1A -TG hearts. Thus, our studies demonstrate, for the first time, a novel mechanism linking basal cardiac contractility directly with RhoA/ROCK signalling, which, in turn, sensitises the contractile machinery to [Ca2+ ]i by enhancing phospho-cMLC2 levels. http://dx.doi.org/10.1016/j.hlc.2013.05.143
ABSTRACTS
Heart, Lung and Circulation 2013;22:S1–S125
56.0 ± 21.5
Non−PH
30.0 ± 5.2
p
0.002
RVDP (mmHg)
RV EDP (mmHg)
CSANZ 2013 Abstracts
dP/dt min (mmHg/s)
dP/dt max (mmHg/s)
RV tau (ms)
IVRT (ms)
5.1 ± 6.6
11.0 ± 6.3 −530 ± 219
521 ± 209
53 ± 32
52 ± 25
−0.1 ± 3.3
3.8 ± 3.7 −304 ± 78
436 ± 146
31 ± 13
38 ± 16
0.03
0.004
0.006
0.27
0.04
0.13
S59
142 Studies of a Mouse Model of Cardiac ␣1A -Adrenergic Receptor Overexpression Provide Evidence For a Critical Role of RhoA/ROCK Signalling in Cardiac Contractility
Conclusion: Pulmonary hypertension is associated with abnormal measures of RV active relaxation and increased RVEDP.
Z. Yu 1,2,3,∗ , J. Tan 1 , A. McMahon 1,2,4 , S. Iismaa 1,3 , X. Xiao 1 , S. Kesteven 1 , M. Reichelt 1,5 , M. Mohl 1 , Y. Dai 1 , A. Sketchley 1 , L. Yang 1 , H. Gong 1 , D. Fatkin 1,2,3 , D. Allen 6 , S. Head 7 , R. Graham 1,2,3 , M. Feneley 1,2,3
http://dx.doi.org/10.1016/j.hlc.2013.05.141
Chang Cardiac Research Institute, Sydney, Australia Department, St Vincent’s Hospital, Sydney, Australia 3 Faculty of Medicine, University of New South Wales, Sydney, Australia 4 ANZAC Research Institute, Sydney, Australia 5 Physiology Department, University of Melbourne, Melbourne, Australia 6 Physiology Department, University of Sydney, Sydney, Australia 7 Physiology Department, University of New South Wales, Sydney, Australia
141 Stretch-Dependent Release of Positively Inotropic Factors in Isolated Perfused Rat Hearts M. Ward ∗ , X. Shen University of Auckland, New Zealand Background: Stretching cardiac muscle gives rise to a biphasic increase in contractility, with the secondary phase accompanied by an increase in the Ca2+ transients (the ‘slow force response’ or SFR). The mechanism that leads to the SFR is still debated. One theory suggests that stretch releases angiotensin II, activating the Na+ –H+ -exchanger, increasing [Na+ ]i and, subsequently, increasing Ca2+ entry by the Na+ /Ca2+ -exchanger. Our aim was to investigate the stretch-dependent release of extra-humoral factors which might mediate the SFR. Methods: Isolated Langendorff-perfused rat hearts were subjected to stretch by increasing the volume of a fluid-filled balloon in the LV. The coronary effluent from stretched and un-stretched hearts was collected via a cannula inserted into the RV and used to superfuse ventricular trabeculae at 2.1 m sarcomere length while measuring [Ca2+ ]i and twitch force. Samples of coronary effluent were also analysed using Liquid Chromatography/Mass Spectroscopy (LC/MS). Results: In trabeculae, the effluent from stretched hearts increased twitch force by 25% (p < 0.01, n = 12) and the [Ca2+ ]i transients by 11.5% (p < 0.05, n = 5), similar to that observed during the SFR. LC/MS analysis revealed an increase in fatty acid related metabolites such as arachidonic acid (AA) and prostaglandins (PG) in the stretched effluent. Both AA and PGF2␣ increased force and [Ca2+ ]i in trabeculae, and the COX inhibitor indomethacin reduced the SFR. Conclusions: Our study confirms that positively inotropic factors are released by stretch that could mediate the SFR, implicating a stretch-dependent signalling pathway downstream of COX. http://dx.doi.org/10.1016/j.hlc.2013.05.142
1 Victor
2 Cardiology
Despite evidence implicating the ␣1A -adrenergic receptor (AR) in the development of cardiac hypertrophy, we have previously reported that transgenic (TG) mice with cardiac-restricted ␣1A -AR overexpression (170-fold) exhibit enhanced ventricular contractility but not hypertrophy in vivo. The present study investigated the role of ␣1A -AR in cardiac contractility. We observed dose-related hypercontractile responses to the ␣1A -AR agonist, A61603, in isolated ␣1A -TG vs non-transgenic littermate (NTL) hearts and cardiomyocytes, which was due to an increased amplitude of the systolic rise in [Ca2+ ]i . In the absence of agonist stimulation, however, isolated ␣1A -TG hearts and cardiomyocytes exhibited reduced contractility despite unchanged [Ca2+ ]i . This basal hypocontractility was associated with decreased RhoA/Rho kinase (ROCK) activity and hypophosphorylation of both myosin phosphatase targeting subunit 1 (MYPT1) and cardiac myosin light chain 2 (cMLC2), all of which were rapidly reversed by the selective ␣1A -AR antagonist, RS100329. We also found that basal contractility in ␣1A -TG and NTL hearts was strongly correlated with RhoA activity and with phospho-MTPY1 and cMLC2 levels. Further, in isolated NTL hearts, inhibition of ROCK with a selective inhibitor, Y-27632, caused a rapid reduction in basal contractility, which phenocopied the basal hypocontractility observed in isolated untreated ␣1A -TG hearts. Thus, our studies demonstrate, for the first time, a novel mechanism linking basal cardiac contractility directly with RhoA/ROCK signalling, which, in turn, sensitises the contractile machinery to [Ca2+ ]i by enhancing phospho-cMLC2 levels. http://dx.doi.org/10.1016/j.hlc.2013.05.143
ABSTRACTS
Heart, Lung and Circulation 2013;22:S1–S125