Calcium currents of olfactory bulb juxtaglomerular cells: profile and multiple conductance plateau potential simulation

摘要

The olfactory glomerulus is the locus of information transfer between olfactory sensory neurons and output neurons of the olfactory bulb. Juxtagiomerular cells (JGCs) may influence intragiomerular processing by firing plateau potentials that support multiple spikes. It is unclear what inward currents mediate this firing pattern. In previous work, we characterized potassium currents of JGCs. We focus here on the inward currents using whole cell current clamp and voltage recording in a rat in vitro slice preparation, as well as computer simulation. We first showed that sodium current was not required to mediate plateau potentials. Voltage clamp characterization of calcium current (I_(Ca)) determined that I_(Ca) consisted of a slow activating, rapidly inactivating (tau_(10%-90% rise) 6-8 ms, tau_(Inactivation) 38-77 ms) component I_(cat1), similar to T-type currents, and a sustained (tau_(inactivation)500 ms) component I_(cat2), likely composed of L-type and P/Q-type currents. We used computer simulation to test their roles in plateau potential firing. We robustly modeled I_(cat1) and I_(cat2) to Hodgkin-Huxley schemes (m~3h and m~2, respectively) and simulated a JGC plateau potential with six conductances: calcium currents as above, potassium currents from our prior study (A-type I_(kt1), D-type I_(kt2), delayed rectifier I_(kt3)), and a fast sodium current (I_(Na)). We demonstrated that I_(cat1) was required for mediating the plateau potential, unlike I_(Na) and I_(cat2), and its tau_(Inactivation) determined plateau duration. We also found that I_(kt1) dictated plateau potential shape more than I_(kt2) and I_(kt3). The influence of these two transient and opposing conductances suggests a unique mechanism of plateau potential physiology.