Effects of estradiol and progesterone on voltage-gated calcium and potassium conductances in rat CA1 hippocampal neurons.

In this study we recorded voltage gated Ca and K conductances with patch electrodes in hippocampal slices from female rats, which were ovariectomized (OVX) 1 week before the experiment. One experimental group was primed with estradiol at day 3 and 4 after OVX and received progesterone 4 hr before the start of the experiment. The second group was treated with estradiol at day 3 and 4, but received vehicle at the day of the experiment. The third group was not treated with hormones (only vehicle injections). We observed that the amplitude of both sustained and transient Ca currents were significantly enhanced in CA1 pyramidal neurons recorded in tissue from estradiol primed rats receiving progesterone when compared to the nontreated OVX controls; without estradiol priming Ca current amplitudes were small. Current amplitudes in tissue from rats treated with estradiol only, were at intermediate values. The voltage for half-maximal steady state inactivation of the transient Ca current was at a less negative value for the estradiol/progesterone treated group in comparison to the OVX controls. Input resistances of the cells, and voltage or kinetic properties of the currents as recorded under these conditions were comparable for the three groups. Characteristics of two voltage gated K conductances, that is, the transient IA and the delayed rectifier, displayed no consistent differences for the three experimental groups. We conclude that long-term modulation of estradiol and progesterone levels alters the Ca but not the K currents that were tested in CA1 pyramidal neurons. These alterations may be linked to steroid-induced morphological changes in dendrites of CA1 pyramidal cells.