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Enhancement by T-type Ca2+ currents of odor sensitivity in olfactory receptor cells
1Department of Physiology, School of Medicine, Fujita Health University, Toyoake, Aichi, 470-1192, Japan. fkawai@fujita-hu.ac.jp
Abstract:
Mechanisms underlying action potential initiation in olfactory receptor cells (ORCs) during odor stimulation were investigated using conventional and dynamic patch-clamp recording techniques. Under current-clamp conditions, action potentials generated by a least effective odor-induced depolarization were almost completely blocked by 0.1 mm Ni(2+), a T-type Ca(2+) channel blocker, but not by 0.1 mm Cd(2+), a high voltage-activated Ca(2+) channel blocker. Under voltage-clamp conditions, depolarizing voltage steps induced a fast transient inward current, which consisted of Na(+) (I(Na)) and T-type Ca(2+) (I(Ca,T)) currents. The amplitude of I(Ca,T) was approximately one-fourth of that of I(Na) (0.23 +/- 0.03, mean +/- SEM). Because both I(Na) and I(Ca,T) are known to show rapid inactivation, we examined how much I(Na) and I(Ca,T) are activated during the gradually depolarizing initial phase of receptor potentials. The ratio of I(Ca,T)/I(Na) during a ramp depolarization at the slope of 0.5 mV/msec was 0.56 +/- 0.03. Using the dynamic patch-clamp recording technique, we also recorded I(Ca,T) and I(Na) during the generation of odor-induced action potentials. This ratio of I(Ca,T)/I(Na) was 0.54 +/- 0.04. These ratios were more than twice as large as that (0.23) obtained from the experiment using voltage steps, suggesting that I(Ca,T) carries significant amount of current to generate the action potentials. We conclude that I(Ca,T) contributes to enhance odor sensitivity by lowering the threshold of spike generation in ORCs.
Insights
T-type calcium channels (I(Ca,T)) significantly contribute to action potential initiation in olfactory receptor cells (ORCs). These channels enhance odor sensitivity by lowering the spike generation threshold, crucial for detecting faint smells.
Area of Science:
- Neuroscience
- Olfactory receptor cell physiology
- Ion channel function
Background:
- Action potential initiation in olfactory receptor cells (ORCs) is critical for odor detection.
- The specific roles of sodium (Na+) and calcium (Ca2+) currents in this process are not fully elucidated.
Purpose of the Study:
- To investigate the mechanisms of action potential initiation in ORCs during odor stimulation.
- To determine the contribution of T-type calcium channels (I(Ca,T)) and sodium currents (I(Na)) to odor-induced action potentials.
Main Methods:
- Conventional and dynamic patch-clamp recording techniques were employed.
- Pharmacological blockade using Ni2+ (T-type Ca2+ channel blocker) and Cd2+ (high voltage-activated Ca2+ channel blocker) was utilized.
- Current-clamp and voltage-clamp recordings were performed to analyze ion channel activity.
Main Results:
- Odor-induced action potentials were significantly blocked by Ni2+, indicating the involvement of T-type Ca2+ channels.
- Under voltage-clamp, T-type calcium currents (I(Ca,T)) constituted a substantial fraction of the total inward current during depolarization.
- The ratio of I(Ca,T)/I(Na) during odor-induced action potentials was significantly higher than that measured during voltage steps, suggesting a critical role for I(Ca,T) in spike generation.
Conclusions:
- T-type calcium channels play a significant role in action potential initiation in ORCs.
- I(Ca,T) enhances odor sensitivity by reducing the threshold for spike generation.
- These findings provide insights into the molecular mechanisms of olfactory transduction.