Spatial Distribution And Characteristics Of Voltage-Gated Calcium Signals Within Visual Interneurons. Juergen Haag and Alexander Borst. Friedrich-Miescher-Laboratory of the Max-Planck-Society, Spemannstrasse 37-39, D-72076 Tuebingen.
APStracts 6:0502N, 1999.
Most of our knowledge about insect calcium currents is derived from studies on cultured or dissociated somata. So far, only little data on calcium currents are available for neurons including their dendritic and presynaptic structures. Here, we combined the switched-electrode voltage clamp technique with optical recording using calcium sensitive dyes in identified fly visual interneurons in vivo in order to characterize the voltage dependence and dynamics of calcium currents quantitatively and in a spatially resolved way. For all three cell types considered, i.e. CH-, HS- and VS-cells, the activation curve is rather flat and covers a voltage range from -60 to -20 mV in dendritic as well as presynaptic areas of the cells. The calcium increase is fastest for CH-cells with a time constant of about 70 ms. In HS- and VS-cells the time constant amounts to 400 - 700 ms. The calcium dynamics as determined in different regions of the cells are similar, except for a small segment between the axon and the dendrite in HS- and VS-cells, where the calcium increase is significantly faster. In summary, the results show the existence of a low-voltage-activated calcium current with little or no inactivation in dendritic as well as presynaptic regions of fly LPTCs.
Received 28 June 1999; accepted in final form 5 October 1999.
APS Manuscript Number J521-9.
Article publication pending Journal of Neurophysiology.
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 21 December 1999