Submitted on June 27, 2007
Accepted on November 13, 2007
Functional Parameters of Voltage Activated Ca2+ Currents from Olfactory Interneurons in the Antennal Lobe of Periplaneta americana
Andreas Husch1, Simon Hess1, and Peter Kloppenburg1*
1 Institute of Zoology & Physiology, University of Cologne, Cologne, Germany
* To whom correspondence should be addressed. E-mail: peter.kloppenburg{at}uni-koeln.de.
Towards 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 analysed in 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. ICa was isolated and identified using pharmacological, voltage and ion substitution protocols. ICa consisted of a transient and a sustained component. The decay of the transient component was largely Ca2+-dependent. In vitro, ICa had an activation threshold of -50mV with a maximal peak current at -7mV and a half-maximal voltage (V0.5act) for tail current activation of -18mV. In situ, these parameters were significantly shifted to more depolarised membrane potentials: ICa activated at -40mV with a maximal peak current at 8mV and a V0.5act for tail current activation of -11mV. The sensitivity of ICa to the divalent cations Cd2+, Co2+, and Ni2+ was dose-dependent. The most effective blocker was Cd2+ with an IC50 of 10-5M followed by Ni2+ (IC50 = 3.13 x 10-3M) and Co2+ (IC50 = 1.06 x 10-3M). The organic channel blockers verapamil, diltiazem and nifidepine also blocked ICa in a dose-dependent way and had differential effects on the current waveform. Verapamil blocked ICa with an IC50 of 1.5 x 10-4M and diltiazem had an IC50 of 2.87 x 10-4M. Nifedipine blocked ICa by 33% at 10-4M.
