Modulation Of Transient Outward And Delayed Rectifier Potassium Channels In Acutely Isolated Hippocampal Neurons By Lanthanum

ObjectiveThe effect of extracellular and intracellular La³⁺ on the IA, IK of hippocampal neurons were investigated by using the whole-cell patch-clamp technique in order to analyze how the La³⁺ modulates the IA and IK channels. Using La³⁺ as an ion probe, we compared the modulation of intracellular La³⁺ with that of extracellular La³⁺ to explore the clues for explaining the differences on the relationship between structure and function of IA and IK.MethodsThe effect of extracellular and intracellular La³⁺ on the activation, inactivation and deactivation of IA, IK were investigated on actely isolated rat hippocampal neurons by the enzymolysis method combined with the use of mechanical separation, by using the whole-cell patch-clamp technique.Results1. Extracellular application of 100μmol/L La³⁺ evidently lowered the amplitude of IA and shifted the voltage midpoint of steady-state activation curve of IA from 2.08±2.58mV to depolarizing 22.97±7.28mV(n=24, P<0.001), and decreased the slope-factor (k), but failed to affect IK; intracellular application of 100μmol/L La³⁺ shifted the voltage midpoint of steady-state activation curve of IK from 23.19±5.21mV parallel to hyperpolarized 13.39±1.51mV (n=17, P<0.001), but failed to affect IA.2. Extracellular application of 100μmol/L La³⁺ shifted the steady-state inactivation curve of IA to more depolarized, lift the values of Vh from -48.86±7.95 mV to 9.66±5.44 mV and increased k from 20.49±4.85mV to 24.97±5.36mV (n=17, P<0.01); intracellular application of 100μmol/L La³⁺ shifted the steady-state inactivation curve of IA parallel to depolarized and attenuated the degree of right shift of steady-state inactivation curve of IA caused by the extracellular application La³⁺.3. The extracellular 100μmol/L La³⁺ suppressed the kinetics of IA activation, prolonged the time constant of activation ofÏ„from 1.29±0.05ms to 6.65±0.75ms (n=3, P<0.001) at 30mV, and from 1.04±0.09ms to 2.43±0.13ms (n=3, P<0.001) at 80mV before and after application of La³⁺ respectively.4. The extracellular 100μmol/L La³⁺ delayed the kinetics of IA inactivation, and prolonged the time constant of inactivation ofÏ„from 48.02±13.26 ms to 109.12±17.83ms (n=5, P<0.001) at 30mV, and from 49.55±11.95ms to 97.81±24.97ms (n=5, P<0.001) at 80mV before and after application of La³⁺ respectively.5. The extracellular La³⁺ slowed the time constants of recovery from inactivation of IA from 14.48±1.43ms to 22.62±1.21ms (n=3, P<0.01).6. The extracellular 20mmol/L Ca2+ shifted the steady-state activation curve of IA to more depolarized, increased the Vh and decreased k. In the different groups, the steady-state activation curve of IA was shifted to the right, and k was decreased. However, there was no evident difference to the steady-state activation curve of IA among different groups with the orders: first La³⁺ then Ca2+, or first Ca2+then La³⁺, or simultaneous.Conclusions1. The extracellular La³⁺ suppressed the kinetics of IA activation, delayed the kinetics of IA inactivation and slowed the time constants of recovery from inactivation of IA, and the effect on activation was voltage-dependent, the extracellular La³⁺ stabilized the states of activation, inactivation and deinactivation of IA.2. The extracellular La³⁺ shifted the voltage midpoint of steady-state activation curve of IA to depolarized, but failed to affect IK; the intracellular La³⁺ shifted the voltage midpoint of steady-state activation curve of IK parallel to hyperpolarized, but failed to affect IA; This difference may point out that there are differences in the relationship between structure and function of IA and IK.3. The extracellular and intracellular La³⁺ shifted the steady-state inactivation curve of IA to depolarized, the extracellular La³⁺ may effect on IA steady-state inactivation in part via the intracellular second messenger.4. The modulation of IA, IK by La³⁺ may be resulted from La³⁺ binding to the special site in channel protein.