TY - JOUR T1 - Regional properties of calcium entry in barnacle neurons determined with Arsenazo III and a photodiode array JF - The Journal of Neuroscience JO - J. Neurosci. SP - 1148 LP - 1159 DO - 10.1523/JNEUROSCI.06-04-01148.1986 VL - 6 IS - 4 AU - WN Ross AU - LL Stockbridge AU - NL Stockbridge Y1 - 1986/04/01 UR - http://www.jneurosci.org/content/6/4/1148.abstract N2 - Calcium changes were simultaneously measured at many positions on individual neurons from the supraesophageal ganglion of the barnacle by detecting absorbance changes of the indicator dye Arsenazo III with a 10 X 10 photodiode array. These changes were correlated with positions on the stimulated cell determined from Lucifer yellow injections. Absorbance signals were found at all locations on the cells, demonstrating that calcium channels were distributed on the somata, axons, and neuropil processes. By comparing the amplitude of the signal with the membrane area in each region, we could measure the calcium entry per impulse per unit of surface in each part of the cell. Assuming that the properties of the calcium channels are the same in all regions, we determined that calcium channels were distributed uniformly along the commissural axon of one cell and were found at higher density in the neuropil. Because significant calcium changes are only detected when cells are depolarized above about -20 mV, the presence of absorbance signals indicates membrane depolarization above this level. We used this fact to show that calcium spikes propagate along the axon and into the neuropil of one cell, along the axon of another, and not at all in a third. Differences in time course of calcium transients were observed in different regions of cells. The recovery time course was faster at the edge of the cell body than in the center and faster in the neuropil than in the axon or soma. During trains of action potentials or during wide action potentials in tetraethylammonium (TEA) saline, the calcium signal reached a plateau in the neuropil while continuing to rise in the axon and soma. ER -