The subcellular mechanisms underlying these gender differences in cardiac contractile function are not understood. In this study we measure gap27 shape and duration and correlate this with the L-type Ca2+ current (ICaL), a main current that underlies the action potential plateau. Since the length of the action potential influences the amount of Ca2+ stored in the sarcoplasmic reticulum (SR) and therefore the amount of Ca2+ available for contraction we also investigated how SR content varies with gender.
Methods
Animals. We used male and female Dunkin Hartley guinea-pigs since their ECG [6], the ionic currents shaping the ventricular action potentials and excitation–contraction coupling in this species are similar to humans [7] and [8]. Peak plasma testosterone in guinea pigs is achieved at 7 weeks of age equivalent to 530 g in weight so we used males over this weight and designated them as being sexually mature [9]. Females were designated mature if their weight was greater than 330 g, this being the average weight at first oestrus [10]. Mature female animals were chosen at random stages of their oestrus cycle. The investigation conforms to the Guide for the Care and Use of Laboratory Animals published by the US National Institutes of Health (NIH Publication No. 85-23, revised 1996).
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