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Age and ovariectomy abolish beneficial effects of female sex on rat ventricular myocytes exposed to simulated ischemia and reperfusion.

Ross JL, Howlett SE - PLoS ONE (2012)

Bottom Line: Cell shortening (edge detector) and intracellular Ca(2+) (fura-2) were measured simultaneously.However, contraction amplitudes were reduced in reperfusion in male myocytes, while contractions recovered to exceed control levels in females (62.6±5.1 vs. 140.1±15.8%; p<0.05).Age and OVX abolish these beneficial effects and induce Ca(2+) dysregulation at the level of the cardiomyocyte.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada.

ABSTRACT
Sex differences in responses to myocardial ischemia have been described, but whether cardiomyocyte function is influenced by sex in the setting of ischemia and reperfusion has not been elucidated. This study compared contractions and intracellular Ca(2+) in isolated ventricular myocytes exposed to ischemia and reperfusion. Cells were isolated from anesthetized 3-month-old male and female Fischer 344 rats, paced at 4 Hz (37°C), exposed to simulated ischemia (20 mins) and reperfused. Cell shortening (edge detector) and intracellular Ca(2+) (fura-2) were measured simultaneously. Cell viability was assessed with Trypan blue. Ischemia reduced peak contractions and increased Ca(2+) levels equally in myocytes from both sexes. However, contraction amplitudes were reduced in reperfusion in male myocytes, while contractions recovered to exceed control levels in females (62.6±5.1 vs. 140.1±15.8%; p<0.05). Only 60% of male myocytes excluded trypan blue dye after ischemia and reperfusion, while all female cardiomyocytes excluded the dye (p<0.05). Parallel experiments were conducted in myocytes from ∼24-month-old female rats or 5-6-month-old rats that had an ovariectomy at 3-4 weeks of age. Beneficial effects of female sex on myocyte viability and contractile dysfunction in reperfusion were abolished in cells from 24-month-old females. Aged female myocytes also exhibited elevated intracellular Ca(2+) and alternans in ischemia. Cells from ovariectomized rats displayed increased Ca(2+) transients and spontaneous activity in ischemia compared to sham-operated controls. None of the myocytes from ovariectomized rats were viable after 15 minutes of ischemia, while 75% of sham cells remained viable at end of reperfusion (p<0.05). These findings demonstrate that cardiomyocytes from young adult females are more resistant to ischemia and reperfusion injury than cells from males. Age and OVX abolish these beneficial effects and induce Ca(2+) dysregulation at the level of the cardiomyocyte. Thus, beneficial effects of estrogen in ischemia and reperfusion are mediated, in part, by effects on cardiomyocytes.

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Aging was associated with the appearance of mechanical and Ca2+ transient alternans in ischemia in myocytes from female rats.A. Representative example of Ca2+ transient alternans (top) and mechanical alternans (bottom) ratios recorded in an aged female myocyte during ischemia. The occurrence of alternans was quantified as an alternans ratio with the following formula: alternans ratio  = 1 - S/L, where S  =  the amplitude of the small beat and L =  the amplitude of the large beat. Both the mechanical alternans ratio (B) and the Ca2+ transient alternans ratio (C) were significantly higher in myocytes from aged females than in young adult females. The * denotes significantly different from young adult female value (p<0.05; n = 10 young adult female cells and 7 aged female cells).
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pone-0038425-g005: Aging was associated with the appearance of mechanical and Ca2+ transient alternans in ischemia in myocytes from female rats.A. Representative example of Ca2+ transient alternans (top) and mechanical alternans (bottom) ratios recorded in an aged female myocyte during ischemia. The occurrence of alternans was quantified as an alternans ratio with the following formula: alternans ratio  = 1 - S/L, where S  =  the amplitude of the small beat and L =  the amplitude of the large beat. Both the mechanical alternans ratio (B) and the Ca2+ transient alternans ratio (C) were significantly higher in myocytes from aged females than in young adult females. The * denotes significantly different from young adult female value (p<0.05; n = 10 young adult female cells and 7 aged female cells).

Mentions: As aging was associated with increased Ca2+ loading in ischemia, this could promote abnormal activity and spontaneous Ca2+ release in ischemia and reperfusion. There was no evidence of spontaneous activity in ischemia or reperfusion in myocytes from aged rats, as in the younger adult animals (data not shown). However, ischemia did induce mechanical and Ca2+ transient alternans in myocytes from aged female rats, but not in cell from the younger female animals (Figure 5A). These responses were quantified with an alternans ratio as described in the methods section. Results showed mechanical (Figure 5B) and Ca2+ transient alternans ratios (Figure 5C) were increased dramatically in aged myocytes when compared to the younger group. Together, these results show that aging disrupted cardiomyocyte Ca2+ handling in myocytes from female hearts.


Age and ovariectomy abolish beneficial effects of female sex on rat ventricular myocytes exposed to simulated ischemia and reperfusion.

Ross JL, Howlett SE - PLoS ONE (2012)

Aging was associated with the appearance of mechanical and Ca2+ transient alternans in ischemia in myocytes from female rats.A. Representative example of Ca2+ transient alternans (top) and mechanical alternans (bottom) ratios recorded in an aged female myocyte during ischemia. The occurrence of alternans was quantified as an alternans ratio with the following formula: alternans ratio  = 1 - S/L, where S  =  the amplitude of the small beat and L =  the amplitude of the large beat. Both the mechanical alternans ratio (B) and the Ca2+ transient alternans ratio (C) were significantly higher in myocytes from aged females than in young adult females. The * denotes significantly different from young adult female value (p<0.05; n = 10 young adult female cells and 7 aged female cells).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3368849&req=5

pone-0038425-g005: Aging was associated with the appearance of mechanical and Ca2+ transient alternans in ischemia in myocytes from female rats.A. Representative example of Ca2+ transient alternans (top) and mechanical alternans (bottom) ratios recorded in an aged female myocyte during ischemia. The occurrence of alternans was quantified as an alternans ratio with the following formula: alternans ratio  = 1 - S/L, where S  =  the amplitude of the small beat and L =  the amplitude of the large beat. Both the mechanical alternans ratio (B) and the Ca2+ transient alternans ratio (C) were significantly higher in myocytes from aged females than in young adult females. The * denotes significantly different from young adult female value (p<0.05; n = 10 young adult female cells and 7 aged female cells).
Mentions: As aging was associated with increased Ca2+ loading in ischemia, this could promote abnormal activity and spontaneous Ca2+ release in ischemia and reperfusion. There was no evidence of spontaneous activity in ischemia or reperfusion in myocytes from aged rats, as in the younger adult animals (data not shown). However, ischemia did induce mechanical and Ca2+ transient alternans in myocytes from aged female rats, but not in cell from the younger female animals (Figure 5A). These responses were quantified with an alternans ratio as described in the methods section. Results showed mechanical (Figure 5B) and Ca2+ transient alternans ratios (Figure 5C) were increased dramatically in aged myocytes when compared to the younger group. Together, these results show that aging disrupted cardiomyocyte Ca2+ handling in myocytes from female hearts.

Bottom Line: Cell shortening (edge detector) and intracellular Ca(2+) (fura-2) were measured simultaneously.However, contraction amplitudes were reduced in reperfusion in male myocytes, while contractions recovered to exceed control levels in females (62.6±5.1 vs. 140.1±15.8%; p<0.05).Age and OVX abolish these beneficial effects and induce Ca(2+) dysregulation at the level of the cardiomyocyte.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada.

ABSTRACT
Sex differences in responses to myocardial ischemia have been described, but whether cardiomyocyte function is influenced by sex in the setting of ischemia and reperfusion has not been elucidated. This study compared contractions and intracellular Ca(2+) in isolated ventricular myocytes exposed to ischemia and reperfusion. Cells were isolated from anesthetized 3-month-old male and female Fischer 344 rats, paced at 4 Hz (37°C), exposed to simulated ischemia (20 mins) and reperfused. Cell shortening (edge detector) and intracellular Ca(2+) (fura-2) were measured simultaneously. Cell viability was assessed with Trypan blue. Ischemia reduced peak contractions and increased Ca(2+) levels equally in myocytes from both sexes. However, contraction amplitudes were reduced in reperfusion in male myocytes, while contractions recovered to exceed control levels in females (62.6±5.1 vs. 140.1±15.8%; p<0.05). Only 60% of male myocytes excluded trypan blue dye after ischemia and reperfusion, while all female cardiomyocytes excluded the dye (p<0.05). Parallel experiments were conducted in myocytes from ∼24-month-old female rats or 5-6-month-old rats that had an ovariectomy at 3-4 weeks of age. Beneficial effects of female sex on myocyte viability and contractile dysfunction in reperfusion were abolished in cells from 24-month-old females. Aged female myocytes also exhibited elevated intracellular Ca(2+) and alternans in ischemia. Cells from ovariectomized rats displayed increased Ca(2+) transients and spontaneous activity in ischemia compared to sham-operated controls. None of the myocytes from ovariectomized rats were viable after 15 minutes of ischemia, while 75% of sham cells remained viable at end of reperfusion (p<0.05). These findings demonstrate that cardiomyocytes from young adult females are more resistant to ischemia and reperfusion injury than cells from males. Age and OVX abolish these beneficial effects and induce Ca(2+) dysregulation at the level of the cardiomyocyte. Thus, beneficial effects of estrogen in ischemia and reperfusion are mediated, in part, by effects on cardiomyocytes.

Show MeSH
Related in: MedlinePlus