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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.Ischemia reduced peak contractions and increased Ca(2+) levels equally in myocytes from both sexes.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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Myocytes from female rats exhibited less ischemia and reperfusion injury than cells from males.The protocol is as described in the legends to Figures 1 and 2. A. Mean magnitudes of contractions in male (filled squares) and female (filled circles) myocytes exposed to ischemia and reperfusion. B. Mean peak Ca2+ transients recorded from male and female myocytes at 5 minute intervals throughout exposure to ischemia and reperfusion. Average levels of diastolic Ca2+ (C) and resting myocyte length (D) recorded throughout the experimental protocol in cells from males and females. In all cases, data were normalized to values recorded after 15 minutes of stimulation. E. Survival curves illustrating the viability of male (dashed line) and female (solid line) cells at 5 minute intervals throughout the experimental protocol. The * denotes significantly different from young adult male value (p<0.05; n = 12 male cells and 10 female cells).
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pone-0038425-g003: Myocytes from female rats exhibited less ischemia and reperfusion injury than cells from males.The protocol is as described in the legends to Figures 1 and 2. A. Mean magnitudes of contractions in male (filled squares) and female (filled circles) myocytes exposed to ischemia and reperfusion. B. Mean peak Ca2+ transients recorded from male and female myocytes at 5 minute intervals throughout exposure to ischemia and reperfusion. Average levels of diastolic Ca2+ (C) and resting myocyte length (D) recorded throughout the experimental protocol in cells from males and females. In all cases, data were normalized to values recorded after 15 minutes of stimulation. E. Survival curves illustrating the viability of male (dashed line) and female (solid line) cells at 5 minute intervals throughout the experimental protocol. The * denotes significantly different from young adult male value (p<0.05; n = 12 male cells and 10 female cells).

Mentions: To determine whether responses to ischemia and reperfusion differed significantly between the sexes, contractions and underlying Ca2+ transients were directly compared as shown in Figure 3. Peak contractions were reduced by ischemia to a similar degree in cells from males and females (Figure 3A). However, while peak contractions were reduced throughout most of reperfusion in male myocytes, contractions in female cardiomyocytes actually fully recovered and were significantly larger than males in reperfusion (Figure 3A). Peak Ca2+ transients (Figure 3B) and diastolic Ca2+ levels (Figure 3C) were similar in male and female myocytes during ischemia and reperfusion, and the degree of hypercontracture in reperfusion did not differ between the two groups (Figure 3D). In contrast, exposure to Trypan blue revealed a significant difference in cell viability between the sexes. Although all myocytes in the young female group excluded trypan blue after exposure to ischemia and reperfusion, cell viability declined in reperfusion in the young male group and this sex difference was statistically significant (p<0.05). Taken together, these findings showed that myocytes from young adult females were resistant to ischemia and reperfusion injury, while myocytes from young adult males were not.


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)

Myocytes from female rats exhibited less ischemia and reperfusion injury than cells from males.The protocol is as described in the legends to Figures 1 and 2. A. Mean magnitudes of contractions in male (filled squares) and female (filled circles) myocytes exposed to ischemia and reperfusion. B. Mean peak Ca2+ transients recorded from male and female myocytes at 5 minute intervals throughout exposure to ischemia and reperfusion. Average levels of diastolic Ca2+ (C) and resting myocyte length (D) recorded throughout the experimental protocol in cells from males and females. In all cases, data were normalized to values recorded after 15 minutes of stimulation. E. Survival curves illustrating the viability of male (dashed line) and female (solid line) cells at 5 minute intervals throughout the experimental protocol. The * denotes significantly different from young adult male value (p<0.05; n = 12 male cells and 10 female cells).
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3368849&req=5

pone-0038425-g003: Myocytes from female rats exhibited less ischemia and reperfusion injury than cells from males.The protocol is as described in the legends to Figures 1 and 2. A. Mean magnitudes of contractions in male (filled squares) and female (filled circles) myocytes exposed to ischemia and reperfusion. B. Mean peak Ca2+ transients recorded from male and female myocytes at 5 minute intervals throughout exposure to ischemia and reperfusion. Average levels of diastolic Ca2+ (C) and resting myocyte length (D) recorded throughout the experimental protocol in cells from males and females. In all cases, data were normalized to values recorded after 15 minutes of stimulation. E. Survival curves illustrating the viability of male (dashed line) and female (solid line) cells at 5 minute intervals throughout the experimental protocol. The * denotes significantly different from young adult male value (p<0.05; n = 12 male cells and 10 female cells).
Mentions: To determine whether responses to ischemia and reperfusion differed significantly between the sexes, contractions and underlying Ca2+ transients were directly compared as shown in Figure 3. Peak contractions were reduced by ischemia to a similar degree in cells from males and females (Figure 3A). However, while peak contractions were reduced throughout most of reperfusion in male myocytes, contractions in female cardiomyocytes actually fully recovered and were significantly larger than males in reperfusion (Figure 3A). Peak Ca2+ transients (Figure 3B) and diastolic Ca2+ levels (Figure 3C) were similar in male and female myocytes during ischemia and reperfusion, and the degree of hypercontracture in reperfusion did not differ between the two groups (Figure 3D). In contrast, exposure to Trypan blue revealed a significant difference in cell viability between the sexes. Although all myocytes in the young female group excluded trypan blue after exposure to ischemia and reperfusion, cell viability declined in reperfusion in the young male group and this sex difference was statistically significant (p<0.05). Taken together, these findings showed that myocytes from young adult females were resistant to ischemia and reperfusion injury, while myocytes from young adult males were not.

Bottom Line: Cell shortening (edge detector) and intracellular Ca(2+) (fura-2) were measured simultaneously.Ischemia reduced peak contractions and increased Ca(2+) levels equally in myocytes from both sexes.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