[Changes of IA and IK from the pyramidal neurons at hippocampal CA1 during the early development of rats]

Brain growth spurt (BGS) is the critical period of neuronal growth and synaptic connection. The voltage-gated K(+) channel is the key channel for maintenance of cell excitability and information transfer among neurons. The purpose of the present study is to investigate the critical period of voltage-gated K(+) channel development in hippocampal CA1 neurons during the BGS. Changes of voltage-gated K(+) currents in neurons from acutely isolated hippocampal CA1 brain slices of rats at different ages (0-4 weeks after birth) were recorded by the whole-cell patch-clamp technique. The depolarization voltage was set at +90 mV, and 0 week was set as the control group. The experimental results showed that, with increasing ages (1-4 weeks), the maximum current densities of IA increased by (16.14 ± 0.51)%, (81.73 ± 10.71)%, (106.72 ± 5.29)%, (134.58 ± 8.81)% (n = 10, P < 0.05), and the maximum current densities of IK increased by (16.75 ± 3.88)%, (134.01 ± 2.85)%, (180.56 ± 8.49)%, (194.5 ± 8.53)% (n = 10, P < 0.05), respectively, compared with those in 0 week. During 0-4 weeks after birth, the activation kinetics of IA shifted to left, and the half activation voltages of IA were 14.67 ± 0.75, 13.46 ± 0.64, 8.39 ± 0.87, 4.60 ± 0.96, 0.54 ± 0.92 (mV, n = 10, P < 0.05), respectively; The activation kinetics of IK shifted to left and the half activation voltages of IK were 8.94 ± 0.85, 6.65 ± 0.89, 0.47 ± 1.15, -1.80 ± 0.89, -8.56 ± 1.08 (mV, n = 10, P < 0.05) respectively. The inactivation kinetics of IA also shifted to left, and the half inactivation voltages were -45.68 ± 1.26, -46.81 ± 0.78, -48.64 ± 0.81, -51.96 ± 1.02, -58.31 ± 1.35 (mV, n = 10) respectively at 0, 1, 2, 3 and 4 weeks after birth, which showed no significant changes between 0 and 1 week, but significant decreases during 1-4 weeks after birth (P < 0.05). These results indicate that the current densities of IA and IK increase and the kinetic characteristics of the voltage-gated K(+) channels change with increasing ages during 0-4 weeks after birth, and the differences are especially significant between the 1st week and the 2nd week after birth. These changes may be related to the maturation of hippocampal neurons and the progress of their functions.