CORTICOSTEROID EFFECTS ON SODIUM AND CALCIUM CURRENTS IN ACUTELY DISSOCIATED RAT CA1 HIPPOCAMPAL-NEURONS

Consequences of corricosteroid receptor activation on voltage-dependen t Na+ conductances were studied in acutely dissociated CA1 hippocampal neurons. This preparation was selected because of the compact electro tonic properties of dissociated neurons, allowing reliable voltage-cla mp of the large and fast Na+ currents. The Na+ currents were studied i n (i) neurons of adrenalectomized animals (no steroid receptors occupi ed), (ii) neurons from tissue of adrenalectomized rats treated in vitr o with corticosterone and the glucocorticoid receptor antagonist RU384 86 (selectively occupying the mineralocorticoid receptor), (iii) corti costerone-treated neurons of adrenalectomized animals (occupying both the mineralocorticoid and glucocorticoid receptors) and (iv) neurons o f sham-operated animals. Activation and steady-state inactivation prop erties of the Na+ current recorded in neurons of adrenalectomized anim als were slightly shifted (3-5 mV) to hyperpolarized potentials as com pared to the Na+ currents from neurons of the other experimental group s. Furthermore, the removal from inactivation of the Na+ current in th e group of neurons of adrenalectomized animals was relatively slow. Al though small, these effects could influence neuronal properties like a ction potential generation and accommodation. Under the present experi mental conditions, no apparent differences were seen between cells wit h predominant mineralocorticoid receptor activation and cells where bo th mineralocorticoid and glucocorticoid receptors were occupied. In co ntrast to Na+ currents, voltage-dependent Ca2+ currents displayed no s teroid-dependent shifts in voltage-dependent properties. However, Ca2 current amplitudes were increased by similar to 160% in CA1 neurons o f adrenalectomized animals as compared to Ca2+ currents from neurons o f the other experimental groups. We conclude that corticosteroid recep tor activation affects various properties of voltage-dependent Na+ and Ca2+ conductances in CA1 neurons, indicating that the steroid recepto rs are involved in the modulation of neuronal excitability in these ce lls. (C) 1997 IBRO.