Can 4-chloro-m-cresol be substituted for caffeine as an activator of calcium oscillation in bullfrog sympathetic ganglion cells?

4-Chloro-m-cresol (cresol) and caffeine have been shown to be potent activators of the Ca2+ release mediated by the ryanodine-sensitive Ca2+ release channel and therefore increase the cytosolic free calcium concentration in skeletal muscles. To distinguish the effects of cresol and caffeine in neurones, the responses of the intracellular ([Ca2+]i) and intraluminal free calcium concentrations to cresol were investigated using bullfrog sympathetic ganglion cells and then compared with those to caffeine. Cresol generated a gradual rise (slow response) with and without a fast transient rise (fast response) in [Ca2+]i. A low extracellular Ca2+ concentration abolished the slow response but not the fast response, thus indicating that the slow response was caused by a Ca2+ influx across the cell membrane. The fast response was inhibited by ryanodine, thus confirming that the source may therefore be the Ca2+ release through the ryanodine-sensitive calcium store. Unlike caffeine, the long-term application of cresol did not cause any calcium oscillation; neither did it cause a decrease in the basal calcium levels.