Regional distribution of calcium influx into bursting neurons detected with arsenazo III.

Absorbance changes of the metallochromic indicator arsenazo III were used in conjunction with an array of 100 photodiodes to measure changes in intracellular calcium concentration at many positions simultaneously in identified neurons of the crab stomatogastric ganglion. When stimulated with intrasomatically injected current, several of these neurons showed calcium changes all over the cell, indicating that calcium channels were distributed widely in the neuropil and on the soma. When the membrane potential was allowed to oscillate without stimulation, absorbance oscillations were detected all over the neuropil but not in the soma. A comparison between the membrane potential recorded in the soma and the calcium signal in the neuropil shows that calcium entry followed the slow voltage oscillation with the peak calcium signal detected 50-150 msec after the end of the voltage plateau.