Figure 1. Intracellular [Ca2+] transients in and glutamate release from cultured neonatal rat cerebellar granule (CG) neurons on a coverslip. Influx of Ca2+and glutamate release were elicited by the abrupt increase of the external [K+] from 5 to 55 mM by the addition of KCl to a stirred solution in the cuvette. Tracings are shown for studies performed in normal extracellular [Ca2+] of 1.2 mM, 0.4 mM, and no added Ca2+(free [Ca2+] was [almost equal to] mM). (A) Intracellular [Ca2+] concentration ([Ca2+]i) was determined in fura-2-loaded cells using the excitation fluorescence ratio method, in which calibration of the ratio was performed by subsequent cell permeabilization (sample rate = 3 Hz). (B) Glutamate release estimated by the fluorescence of NADPH, which is produced from NADP+ in proportion to the amount of glutamate released in the presence of glutamate dehydrogenase (sample rate = 1 Hz). (C) Relation between the peak Ca2+transient and glutamate release in varied external [Ca2+]. Results are expressed as the fraction of same-day control; the points and error bars represent the mean +/- SD. The n values for the peak [Ca2+]iand glutamate, respectively, are in given in parentheses. The dotted line represents the line of unity, i.e., equal changes.