AGE-DEPENDENT EXPRESSION OF HIGH-VOLTAGE ACTIVATED CALCIUM CURRENTS DURING CEREBELLAR GRANULE CELL-DEVELOPMENT IN-SITU

Ca2+ currents play a crucial role during neuronal growth. In this pape r we describe the development of Ca2+ currents using whole-cell patch- clamp recordings in granule cells of cerebellar slices obtained from 7 - to 24-day-old rats. Granule cells expressed high-voltage-activated ( HVA) Ca2+ currents in different proportions. The percentage of cells w ith a measurable HVA current, and the size of HVA current increased in parallel with granule cell maturation. At less than 14 days HVA curre nts consisted of a fast- and slow-inactivating component, while at mor e than 19 days only the slow-inactivating component remained. The fast -inactivating component had faster activation and inactivation kinetic s, a more negative threshold for activation, and steeper steady-state inactivation than the slow-inactivating component. Nifedipine (5 mu M) partially blocked both components. omega-Conotoxin (5 mu M, omega-CgT x) blocked the slow-inactivating component rather selectively. These r esults indicate that HVA currents change their gating and pharmacologi cal properties during development. Although the mechanism at the molec ular level remains speculative, the developmental changes of the HVA c urrent are relevant to the processes of granule cell maturation and ex citability.