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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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In contrast to males, ischemia inhibited Ca2+ transients and promoted recovery of contractile function in reperfusion in myocytes from young adult female rats.Myocytes were stimulated at 4 Hz for 15 minutes, exposed to ischemia for 20 minutes and reperfused for 30 minutes (filled circles). Cells that served as time controls were paced for 65 minutes without exposure to ischemia (open circles). A. Examples of Ca2+ transients (top) and contractions (bottom) recorded from female myocytes at specific times during an experiment. B. Mean amplitudes of contractions in females cells exposed to ischemia and reperfusion compared to time controls. C. Average amplitudes of Ca2+ transients recorded throughout the experiment. Mean levels of diastolic Ca2+ (D) and diastolic cell length (E) recorded throughout the experimental protocol. Responses were normalized to values recorded after 15 minutes of stimulation. The * denotes significantly different from time control (p<0.05; n = 9 time control cells and 10 cells exposed to ischemia and reperfusion).
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pone-0038425-g002: In contrast to males, ischemia inhibited Ca2+ transients and promoted recovery of contractile function in reperfusion in myocytes from young adult female rats.Myocytes were stimulated at 4 Hz for 15 minutes, exposed to ischemia for 20 minutes and reperfused for 30 minutes (filled circles). Cells that served as time controls were paced for 65 minutes without exposure to ischemia (open circles). A. Examples of Ca2+ transients (top) and contractions (bottom) recorded from female myocytes at specific times during an experiment. B. Mean amplitudes of contractions in females cells exposed to ischemia and reperfusion compared to time controls. C. Average amplitudes of Ca2+ transients recorded throughout the experiment. Mean levels of diastolic Ca2+ (D) and diastolic cell length (E) recorded throughout the experimental protocol. Responses were normalized to values recorded after 15 minutes of stimulation. The * denotes significantly different from time control (p<0.05; n = 9 time control cells and 10 cells exposed to ischemia and reperfusion).

Mentions: Parallel ischemia and reperfusion experiments were then performed in myocytes from young adult females. Figure 2A shows representative Ca2+ transients (top) and contractions (bottom) in ventricular myocytes from female rats. Mean data show that contractions decreased significantly in ischemia, but recovered upon reperfusion and exceeded time controls throughout reperfusion (Figure 2B). Peak Ca2+ transients declined in ischemia and early reperfusion in the female group compared to time control cells (Figure 2C). Diastolic Ca2+ levels rose in ischemia and recovered in reperfusion (Figure 2D). Female cells initially exhibited hypercontracture in reperfusion, but this quickly recovered with continued reperfusion (Figure 2E). Spontaneous activity did not occur in either ischemia or reperfusion (not shown). Interestingly, all myocytes from young female rats survived exposure to ischemia and reperfusion.


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)

In contrast to males, ischemia inhibited Ca2+ transients and promoted recovery of contractile function in reperfusion in myocytes from young adult female rats.Myocytes were stimulated at 4 Hz for 15 minutes, exposed to ischemia for 20 minutes and reperfused for 30 minutes (filled circles). Cells that served as time controls were paced for 65 minutes without exposure to ischemia (open circles). A. Examples of Ca2+ transients (top) and contractions (bottom) recorded from female myocytes at specific times during an experiment. B. Mean amplitudes of contractions in females cells exposed to ischemia and reperfusion compared to time controls. C. Average amplitudes of Ca2+ transients recorded throughout the experiment. Mean levels of diastolic Ca2+ (D) and diastolic cell length (E) recorded throughout the experimental protocol. Responses were normalized to values recorded after 15 minutes of stimulation. The * denotes significantly different from time control (p<0.05; n = 9 time control cells and 10 cells exposed to ischemia and reperfusion).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0038425-g002: In contrast to males, ischemia inhibited Ca2+ transients and promoted recovery of contractile function in reperfusion in myocytes from young adult female rats.Myocytes were stimulated at 4 Hz for 15 minutes, exposed to ischemia for 20 minutes and reperfused for 30 minutes (filled circles). Cells that served as time controls were paced for 65 minutes without exposure to ischemia (open circles). A. Examples of Ca2+ transients (top) and contractions (bottom) recorded from female myocytes at specific times during an experiment. B. Mean amplitudes of contractions in females cells exposed to ischemia and reperfusion compared to time controls. C. Average amplitudes of Ca2+ transients recorded throughout the experiment. Mean levels of diastolic Ca2+ (D) and diastolic cell length (E) recorded throughout the experimental protocol. Responses were normalized to values recorded after 15 minutes of stimulation. The * denotes significantly different from time control (p<0.05; n = 9 time control cells and 10 cells exposed to ischemia and reperfusion).
Mentions: Parallel ischemia and reperfusion experiments were then performed in myocytes from young adult females. Figure 2A shows representative Ca2+ transients (top) and contractions (bottom) in ventricular myocytes from female rats. Mean data show that contractions decreased significantly in ischemia, but recovered upon reperfusion and exceeded time controls throughout reperfusion (Figure 2B). Peak Ca2+ transients declined in ischemia and early reperfusion in the female group compared to time control cells (Figure 2C). Diastolic Ca2+ levels rose in ischemia and recovered in reperfusion (Figure 2D). Female cells initially exhibited hypercontracture in reperfusion, but this quickly recovered with continued reperfusion (Figure 2E). Spontaneous activity did not occur in either ischemia or reperfusion (not shown). Interestingly, all myocytes from young female rats survived exposure to ischemia and reperfusion.

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