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Functional Parameters of Voltage-Activated Ca²⁺ Currents From Olfactory Interneurons in the Antennal Lobe of Periplaneta americana

Institute of Zoology and Physiology, University of Cologne, Cologne, Germany

Submitted 27 June 2007; accepted in final form 13 November 2007

Toward our goal to better understand the physiological parameters that mediate olfactory information processing on the cellular level, voltage-activated calcium currents (I_Ca) in olfactory interneurons of the antennal lobe from adult cockroaches were analyzed under two conditions: 1) in acutely dissociated cells (in vitro) and 2) in an intact brain preparation (in situ). The study included an analysis of modulatory effects of potential inorganic and organic Ca²⁺ channel blockers. I_Ca was isolated and identified using pharmacological, voltage, and ion substitution protocols. I_Ca consisted of two components: transient and sustained. The decay of the transient component was largely Ca²⁺ dependent. In vitro, I_Ca had an activation threshold of –50 mV with a maximal peak current at –7 mV and a half-maximal voltage (V_0.5act) for tail-current activation of –18 mV. In situ these parameters were significantly shifted to more depolarized membrane potentials: I_Ca activated at –40 mV with a maximal peak current at 8 mV and a V_0.5act for tail-current activation of –11 mV. The sensitivity of I_Ca to the divalent cations Cd²⁺, Co²⁺, and Ni²⁺ was dose dependent. The most effective blocker was Cd²⁺ with an IC₅₀ of 10^–5 M followed by Ni²⁺ (IC₅₀ = 3.13 x 10^–3 M) and Co²⁺ (IC₅₀ = 1.06 x 10^–3 M). The organic channel blockers verapamil, diltiazem, and nifedipine also blocked I_Ca in a dose-dependent way and had differential effects on the current waveform. Verapamil blocked I_Ca with an IC₅₀ of 1.5 x 10^–4 M and diltiazem had an IC₅₀ of 2.87 x 10^–4 M. Nifedipine blocked I_Ca by 33% at a concentration of 10^–4 M.

This article has been cited by other articles:

				A. Husch, M. Paehler, D. Fusca, L. Paeger, and P. Kloppenburg Calcium Current Diversity in Physiologically Different Local Interneuron Types of the Antennal Lobe J. Neurosci., January 21, 2009; 29(3): 716 - 726. [Abstract] [Full Text] [PDF]