The Impact of Ovariectomy on Calcium Homeostasis and Myofilament Calcium Sensitivity in the Aging Mouse Heart

Abstract

This study determined whether deficiency of ovarian estrogen starting very early in life promoted age-associated Ca2+ dysregulation and contractile dysfunction in isolated ventricular myocytes. Myocytes were isolated from anesthetized C57BL/6 female mice. Animals received an ovariectomy or sham-operation at one month and were aged to ~24 months. Excitation-contraction coupling parameters were compared in fura-2 loaded myocytes (37°C). While Ca2+ transients were larger and faster in field-stimulated myocytes from ovariectomized mice, ovariectomy had no effect on peak fractional shortening. Similarly, ovariectomy had no effect on fractional shortening measured in vivo by echocardiography (values were 60.5 ± 2.9 vs. 60.3 ± 2.5% in sham and ovariectomized, respectively; n=5 mice/group). Ovariectomy did decrease myofilament Ca2+ sensitivity, as evidenced by a 26% increase in the Ca2+ required to activate actomyosin MgATPase in ovariectomized hearts. Larger Ca2+ transients were attributable to a 48% increase in peak Ca2+ current, along with an increase in the amplitude, width and frequency of Ca2+ sparks measured in fluo-4 loaded myocytes. These changes in Ca2+ handling were not due to increased expression of Ca2+ channels (Cav1.2), sarcoplasmic reticulum Ca2+ ATPase (SERCA2) or Na+-Ca2+ exchanger in ovariectomized hearts. However, ovariectomy increased sarcoplasmic reticulum Ca2+ stores by ~90% and promoted spontaneous Ca2+ release from the sarcoplasmic reticulum when compared to sham controls. These observations demonstrate that long-term ovariectomy promotes intracellular Ca2+ dysregulation, reduces myofilament Ca2+ sensitivity and increases spontaneous Ca2+ release in the aging female heart.

Cardiac contraction, calcium transients, and myofilament calcium sensitivity fluctuate with the estrous cycle in young adult female mice

“…If we use an in vitro calibration curve to convert our data to Ca 2ϩ concentration, peak Ca 2ϩ transients are ϳ70 nM in proestrus, metestrus, and diestrus compared with ϳ90 nM in estrus. These values are comparable with those previously reported by our group and others who have used in vitro calibration curves to investigate Ca 2ϩ handling in myocytes from female rodents (e.g., 14,20,66). By contrast, with a similar calibration approach, peak transients are much larger in myocytes from male rodents (e.g., 15,50,56,57).…”

Molecular pathways of oestrogen receptors and β‐adrenergic receptors in cardiac cells: Recognition of their similarities, interactions and therapeutic value

“…Similarly, oestrogen increased expression of NCX, while it was decreased in OVX rats . However, in other studies, no change was observed in the expression of NCX expression in both oestrogen treatment and OVX animals . Although oestrogen decreased the expression of PLB, and OVX increased its expression, no change in expression was found in other reports .…”

“…Similarly, studies examining the role of oestrogen on the expression of LTCC yielded mixed results. Oestrogen decreased LTCC protein levels in rat ventricular myocytes (RVMs), while OVX increased its expression in RVMs, but decreased its expression in mouse ventricular myocytes …”

“…Therefore, the observations that ER and βAR signalling pathways interact may have profound implications on cardiac Ca 2+ regulation and contractility. Furthermore, through ERα, oestrogen altered myofilament Ca 2+ sensitivity . Indeed, in a rat model of angiotensin II‐induced hypertension, OVX exacerbated myofilament Ca 2+ sensitivity, indicating that oestrogen deficiency may play a role in cardiac disorders by lowering the myofilament sensitivity to Ca 2+ …”

Female Heart Health: Is GPER the Missing Link?

“…In one study, NCX expression was increased by E 2 and was decreased in untreated OVX rats (93). In other studies, no change was observed in the expression of NCX expression by estrogen treatment or OVX (25,94). Kravtsov et al (76) determined NCX activity in the heart from OVX rats.…”