Functional parameters of voltage-activated Ca2+ currents from olfactory interneurons in the antennal lobe of Periplaneta americana.
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 Ca(2+) 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 Ca(2+) 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 Cd(2+), Co(2+), and Ni(2+) was dose dependent. The most effective blocker was Cd(2+) with an IC(50) of 10(-5) M followed by Ni(2+) (IC(50)=3.13 x 10(-3) M) and Co(2+) (IC(50)=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 IC(50) of 1.5 x 10(-4) M and diltiazem had an IC(50) of 2.87 x 10(-4) M. Nifedipine blocked I(Ca) by 33% at a concentration of 10(-4) M.
Husch
Andreas
A
Institute of Zoology and Physiology, University of Cologne, Weyertal 119, 50931 Cologne, Germany.
Hess
Simon
S
Kloppenburg
Peter
P
D000818:Animals; D001921:Brain / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002413:Cations, Divalent / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D007395:Interneurons / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009475:Neurons, Afferent / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D009833:Olfactory Pathways / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D010526:Periplaneta / Q000166:cytology / Q000502:physiology*; D012903:Smell / Q000187:drug effects / Q000502:physiology*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002413:Cations, Divalent; D002118:Calcium