Whole-Cell Ion Channel Currents From The Pyramidal Neurons At Hippocampal CA1 During The Early Development Of Rats

【Objective】The characteristics of the ion channels on cell membrane are direct related to the change of the neurons'functions. This dissertation explores the characters of whole cell transmembrane total currents, whole cell sodium current, whole cell potassium currents, transient outward potassium currents and whole cell calcium currents of hippocampal CA1 pyramidal neurons of S-D rats at various ages in the early stages of development. The aim of this study is to explore the critical period of development of ion channel in hippocampus of rats and provide support for studying the development of learning and memory.【Methods】The subject of this dissertation is hippocampus CA1 region pyramidal neurons of rats at different ages, respectively 1,2,3,4 weeks after birth.Characters of whole-cell transmembrane total current, sodium channel current, whole cell potassium channel currents, transient outward potassium channel currents and whole cell calcium channel currents of hippocampal CA1 pyramidal neurons were recorded using patch clamp technique.Curves of I-V, activation, deactivation and recovery after deactivation of whole-cell sodium channel current, transient outward potassium channel current and calcium channel current were obtained via Clampfitl0.2 and Origin7.5.The related parameters, such as half activation voltage, half deactivation voltage, slope factor, recovery time constant, were fitted according to appropriate equations. Statistical tests were performed to study whether there were differences among groups.【Results】1. In the early stages of development, bioactivity of hippocampal slices at different ages were excellent. Structure of hippocampus, Body and axon of the neurons can be observed clearly. The boundary of the neurons has good refractive index and strong sense of three-dimensional under microscope.2. In the early stages of development, I-V curve of sodium channel shifts to the left with increasing age. Maximum current density of sodium channel increases, the corresponding value of maximum current density (pA/pF) is:-139.89±9.47,-147.98±9.39,-229.20±15.42,-271.54±22.78. We can find current density on CA1 neurons of 2-3 weeks after birth increases more significantly than others; The activation curve of sodium channel shift to the repolarization, the corresponding value of half activation voltages (mV) is:-44.65±0.39,-47.42±0.56,-54.79±0.61,-58.44±0.57; Recovery time constant of sodium channel reduces with increasing age, the corresponding value of recovery time constant (ms) is:9.30±0.64,11.15±0.84, 7.95±0.55,7.18±0.56; We found there are no significant changes in deactivation curve, the corresponding value of half deactivation voltages (mV) in different group is:-52.29±0.73,-51.98±0.94,-51.44±0.72,-49.65±0.73.3. Maximum current density of whole-cell transient outward potassium current increases with increasing age, the corresponding value of maximum current density (pA/pF) is:133.11±14.36,182.10±8.55,212.80±15.98,235.86±14.60; The corresponding value of half activation voltages (mV) is::6.25±2.38,10.88±1.71, 5.31±2.46,2.69±2.75; The corresponding value of half deactivation voltages (mV) is:-58.41±0.59,-56.35±0.90,-58.06±2.13,-60.37±0.90; The corresponding value of recovery time constant (ms) is:33.14±3.19,33.78±4.22,35.13±3.92,36.19±3.62.4. Maximum current density of whole-cell calcium current increases with increasing age, the corresponding value of maximum current density (pA/pF) is:-8.02±0.56,-10.02±0.88,-27.59±1.03,-32.59±1.04, We can find current density on CA1 neurons of 2-3 weeks after birth increases more significantly than others; Both the activation and deactivation curves of whole-cell calcium channel shift to the left, The corresponding value of half activation voltages (mV) is:-6.94±0.11,-4.72±0.41,-11.72±1.05,-12.36±1.32, The corresponding value of half deactivation voltages (mV) is:-5.35±2.06,5.43±1.93,-17.80±3.37,-24.88±2.43.【Conclusions】1. In the early stages of development, the distribution of ion channel and its characters of activation, deactivation, recovery in hippocampal CA1 region pyramidal neurons change with age. That is, ion channel is in developing mode.2. The period of 2-3week after birth is fast developing period of sodium channel in hippocampal CA1 region pyramidal neurons. During this time, the distribution of sodium channel increases significantly; Activation curve of sodium channel shifts to the left as well as half activation voltage remarkably decreases. It indicates that sodium channel is prone to be activated; Recovery curve and recovery time constant show recovery of sodium channel is quicker with age.3.The density of potassium channel in hippocampal CA1 region pyramidal neurons increases significantly with increasing age,. But, no remarkable changes were found in characters of activation, deactivation and recovery.4.During the period of 2-3weeks after birth, calcium channel in hippocampal CA1 region pyramidal neurons develops rapidly. During this time, maximum current density of calcium channel increases significantly. Both the activation and deactivation curves of calcium channel shift to the left, the value of half activation and deactivation voltage obviously decrease. Which indicates that calcium channel is apt to be activated and deactivated.