Identification and physiological characterization of calcium-activated ion channels in vomeronasal sensory neurons of the mouse

• Identifikation und physiologische Charakterisierung von Calcium-aktivierten Ionenkanälen in vomeronasalen sensorischen Neuronen der Maus

Degen, Rudolf; Spehr, Marc (Thesis advisor); Manzini, Ivan (Thesis advisor)

Aachen : RWTH Aachen University (2021)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2021

Abstract

Most mammalian species use the accessory olfactory system, consisting of the vomeronasal organ and the accessory olfactory bulb, to gather information about their environment. The vomeronasal organ contains numerous vomeronasal sensory neurons (VSNs), detecting semiochemicals present in most bodily fluids. Semiochemicals are secreted by conspecifics and predators alike and convey information about them. This information is processed along a relatively simple brain pathway consisting of just three higher brain areas before ultimately leading to a behavioral response. In this Dissertation, I have investigated calcium-dependent signal modulation in VSNs. For this, I have combined electrophysiological patch-clamp recordings with single-cell calcium imaging and laser-guided calcium uncaging. NP-EGTA was degraded in different compartments of VSNs to describe calcium-activated currents. I have found at least two spatially separated and electrophysiological distinct calcium-activated currents. The first calcium-activated current is found at the apical dendritic knob of the vomeronasal neuron, where it most likely conducts chloride in a calcium-dependent way through TMEM16A and TMEM16B channels. I have shown that activation of this chloride current leads to the depolarization of the cell and action potential generation. The second calcium-activated current is located in the VSN soma, hyperpolarizing the cell when activated. Through electrophysiological and pharmacological characterization, I have identified potassium as a central part of the somatic calcium-activated current. By applying the pharmacological ion channel blockers apamin and iberiotoxin for the calcium-activated potassium channels SK and BK, respectively, I have found four distinct populations of VSNs. The majority of cells, 47%, displayed currents sensitive to apamin. I have found that these cells had a calcium-dependent and partially apamin reversible decrease in action potential firing and a shift in membrane potential. In 22 % of VSNs I have found a current sensitive to iberiotoxin. These cells also showed a calcium-dependent decrease in action potential firing and a shift in membrane potential. However, I did not observe a reverse of this effect after Iberiotoxin application. Among the VSNs tested with both pharmacological blockers, 44 % were not sensitive to either of them and therefore had no known calcium-activated potassium current. Additionally, I was also able to isolate blocker-insensitive transient as well as persistent calcium-activated currents in a subset of cells, indicating the presence of additional calcium-activated ion channels in VSNs. Ion exchange experiments raise the possibility of calcium-activated non-specific cation channels and calcium-activated chloride channels in VSN somata. Summarized, I propose a heterogeneous population of VSNs, with varying calcium-activated ion channel expression profiles.

Institutions

• Department of Biology [160000]
• Chemosensation Laboratory [163310]