Effects of ovariectomy and 17β-oestradiol replacement on [Ca2+]i in female rat cardiac myocytes

1. The present study investigated the effects of ovariectomy (OVX) and 17beta-oestradiol replacement on [Ca(2+)](i) in rat freshly isolated cardiac myocytes. 2. Myocytes were isolated from the hearts of sham, OVX and OVX + 17beta-oestradiol-replaced female rats by enzymatic digestion with collagenase. Changes in [Ca(2+)](i) in response to varied extracellular [Ca(2+)] were measured using the Ca(2+)- sensitive dye fura-2, with the contractile responses of each cell measured as cell shortening. 3. Increasing extracellular [Ca(2+)] resulted in increased [Ca(2+)](i), in all three groups. Peak [Ca(2+)](i) and the amplitude of the Ca(2+) transient were significantly greater (P < 0.01) in cells from OVX animals compared with cells from both sham and 17 beta-oestradiol-replaced OVX animals. 4. The time-course of decay of the Ca(2+) transient was significantly faster (P < 0.02) in OVX cells compared with both sham and 17beta-oestradiol-replaced cells. In addition, time to 50% relaxation was significantly faster (P < 0.04) and extent of shortening significantly greater (P < 0.01) in OVX cells than in either sham or 17beta-oestradiol cells. 5. These data demonstrate clear differences in peak [Ca(2+)](i) and the amplitude of the Ca(2+) transient between OVX female rat cardiac myocytes compared with intact and 17beta-oestradiol-replaced OVX female rat cardiac myocytes. This suggests that oestrogen may play a long-term role in limiting Ca(2+) entry into the cardiac myocyte.