Effects of gender on intracellular [Ca2+] in rat cardiac myocytes

The present study investigated the effects of gender on intracellular [Ca(2+)] ([Ca(2+)](i)) in freshly isolated rat cardiac myocytes. Changes in [Ca(2+)](i) in response to varied extracellular [Ca(2+)]. different stimulus frequencies and addition of caffeine and isoprenaline were monitored using fura-2 in both male and female cardiac myocytes. Increasing extracellular [Ca(2+)] and stimulus frequency resulted in significant increases in peak [Ca(2+)] and the amplitude of the Ca(2+) transient in both male and female cardiac myocytes. However, as extracellular [Ca(2+)] was raised, peak [Ca(2+)] and the amplitude of the Ca(2+) transient increased significantly more in male than female cardiac myocytes. In addition a significant difference between male and female cells at each stimulus frequency was apparent. The time course of decay of the Ca(2+) transient was significantly slower in female cardiac myocytes when compared with male cardiac myocytes, along with significantly slowed times to peak shortening and 50% relaxation, and a reduced extent of shortening. There was no significant difference in the amplitude of caffeine-induced [Ca(2+)](i) responses between male and female cells, however, [Ca(2+)](i) increased more readily in male cells than in female cells when isoprenaline was added. The data demonstrate that, under a variety of conditions, intracellular [Ca(2+)] rises to higher levels in cardiac myocytes from male as compared to female rats.