Differential expression of voltage-sensitive K+ and Ca2+ currents in neurons of the honeybee olfactory pathway
2003
SUMMARY 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 Ca 2+ 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 Ca 2+ 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 Ca 2+ 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 .
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