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The Journal of Experimental Biology 206, 117-129 (2003)
doi: 10.1242/jeb.00053

Differential expression of voltage-sensitive K⁺ and Ca²⁺ currents in neurons of the honeybee olfactory pathway

Bernd Grünewald

Institut für Biologie, Neurobiologie, Freie Universität Berlin, Königin-Luise-Strasse 28/30, D-14195 Berlin, Germany

e-mail: gruenewa{at}neurobiologie.fu-berlin.de

Accepted 26 September 2002

In order to understand the neuronal processes underlying olfactory learning, biophysical properties such as ion channel activity need to be analysed within neurons of the olfactory pathway. This study analyses voltage-sensitive ionic currents of cultured antennal lobe projection neurons and mushroom body Kenyon cells in the brain of the honeybee Apis mellifera. Rhodamine-labelled neurons were identified in vitro prior to recording, and whole-cell K⁺ and Ca²⁺ currents were measured. All neurons expressed transient and sustained outward K⁺ currents, but Kenyon cells expressed higher relative amounts of transient A-type K⁺ (I_K,A) currents than sustained delayed rectifier K⁺ current (I_K,V). The current density of the I_K,V was significantly higher in projection neurons than in Kenyon cells. The voltage-dependency of K⁺ currents at positive membrane potentials was linear in Kenyon cells, but N-shaped in projection neurons. Blocking of voltage-sensitive Ca²⁺ currents transformed the N-shaped voltage-dependency into a linear one, indicating activation of calcium-dependent K⁺ currents (I_K,Ca). The densities of currents through voltage-sensitive Ca²⁺ channels did not differ between the two neuron classes and the voltage-dependency of current activation was similar. Projection neurons thus express higher calcium-dependent K⁺ currents. These analyses revealed that the various neurons of the honeybee olfactory pathway in vitro have different current phenotypes, which may reflect functional differences between the neuron types in vivo.

Key words: patch clamp, mushroom body, antennal lobe, insect, calcium-dependent K⁺ current, honeybee, Apis mellifera, neuron, olfactory

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