Simulation of Ca2+persistent inward currents in spinal motoneurones: mode of activation and integration of synaptic inputs

摘要: The goal of this study was to investigate the nature activation dendritic calcium persistent inward current (Ca2+ PIC) and its contribution enhancement summation synaptic inputs in spinal motoneurones. A compartmental cable model a cat α-motoneurone developed comprising realistic distribution Ia-afferent synapses low-voltage-activated L-type (Cav1.3) channels distributed over dendrites manner that previously shown match wide set experimental measurements. level systematically increased resulting firing rate, somatic membrane potentials, Cav1.3 channel conductance, Ca2+ PIC were measured. Our simulation results suggest during cell is not activated an all-or-none manner. Instead, it initially graded with increasing input until reaches full level, after which additional increases result minimal changes (PIC saturated). range occurs when recruited causes steep increase frequency as increased, coinciding secondary frequency–current (F–I) relationship. Once saturated slope F–I relationship reduced, corresponding tertiary firing. When post-spike afterhyperpolarization (AHP) blocked, either directly by blocking calcium-activated potassium channels, or indirectly sodium spikes, input. Thus, AHP serves limit depolarization enables graded, rather than all-or-none, PIC. (linear) linear inputs. In contrast, enhances constant amount (constant current), leads less-than multiple These predictions improve our understanding mode role integration