Kinetic parameters of calcium currents in maturing acutely isolated CA1 cells

Calcium currents were recorded in CA1 hippocampal cells from immature (P4-1 0) and older (P22-55) rats, using whole-cell voltage clamp techniques. Para meters defining the voltage-dependence of activation (tau (m)) and inactiva tion (tau (h)), steady-state inactivation and activation were determined at both stages of maturation. Current density increased with maturation. A tr ansient low voltage activated (l.v.a.) current was found in P4-10 cells, bu t not in the older cells. At voltages less negative than -30 mV, current in activation was best described by two exponentials (tau (hf),tau (hs)); the ratio of the amplitudes of the two components changed with maturation, with a dominance of the faster component (tau (hf)) in the younger cells. The v oltage dependence of tau (hf) followed a simple dependence model, decreased with increasing depolarization, in all cells at both stages of maturation. In P4-10 cells. tau (hs) was voltage insensitive (range -25 to +30 mV); in P22-55 cells, the voltage dependence of tau (hs) was found to be complex. Two current components were identified from the voltage dependence of the c onductance in both groups. The first, more hyperpolarized component, the l. v.a. current found in P4-10 cells; this was absent in the older cells, in w hich we found a component with a different voltage dependence. The voltage dependence of the conductance of the second, more depolarized component did not differ in younger and older cells. In the course of maturation, the st eady-state inactivation of the second component underwent a hyperpolarizing shift and a decrease in voltage sensitivity. (C) 2000 Elsevier Science B.V . All rights reserved.