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The Journal of Neuroscience, 2001, 21:RC144:1-5

RAPID COMMUNICATION
Enhancement by T-Type Ca²⁺ Currents of Odor Sensitivity in Olfactory Receptor Cells

Fusao Kawai and Ei-ichi Miyachi

Department of Physiology, School of Medicine, Fujita Health University, Toyoake, Aichi, 470-1192, Japan

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 Ni²⁺, a T-type Ca²⁺ channel blocker, but not by 0.1 mM Cd²⁺, a high voltage-activated Ca²⁺ channel blocker. Under voltage-clamp conditions, depolarizing voltage steps induced a fast transient inward current, which consisted of Na⁺ (I_Na) and T-type Ca²⁺ (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.

Key words: odorant; amyl acetate; odor response; T-type Ca²⁺ channel; newt; action potential; patch clamp

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