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

Abstract

Toward our goal to better understand the physiological parameters that mediate olfactory information processing on the cellular level, voltage-activated calcium currents ( ICa) 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. ICawas isolated and identified using pharmacological, voltage, and ion substitution protocols. ICaconsisted of two components: transient and sustained. The decay of the transient component was largely Ca2+dependent. In vitro, ICahad an activation threshold of −50 mV with a maximal peak current at −7 mV and a half-maximal voltage ( V0.5act) for tail-current activation of −18 mV. In situ these parameters were significantly shifted to more depolarized membrane potentials: ICaactivated at −40 mV with a maximal peak current at 8 mV and a V0.5actfor tail-current activation of −11 mV. The sensitivity of ICato the divalent cations Cd2+, Co2+, and Ni2+was dose dependent. The most effective blocker was Cd2+with an IC50of 10−5M followed by Ni2+(IC50= 3.13 × 10−3M) and Co2+(IC50= 1.06 × 10−3M). The organic channel blockers verapamil, diltiazem, and nifedipine also blocked ICain a dose-dependent way and had differential effects on the current waveform. Verapamil blocked ICawith an IC50of 1.5 × 10−4M and diltiazem had an IC50of 2.87 × 10−4M. Nifedipine blocked ICaby 33% at a concentration of 10−4M.