Impaired calcium release in cerebellar Purkinje neurons maintained in culture

Cerebellar Purkinje neurons demonstrate a form of synaptic plasticity that, in acutely prepared brain slices, has been shown to require calcium release from the intracellular calcium stores through inositol trisphosphate (InsP₃) receptors. Similar studies performed in cultured Purkinje cells, however, find little evidence for the involvement of InsP₃ receptors. To address this discrepancy, the properties of InsP₃- and caffeine-evoked calcium release in cultured Purkinje cells were directly examined. Photorelease of InsP₃ (up to 100 μM) from its photolabile caged analogue produced no change in calcium levels in 70% of cultured Purkinje cells. In the few cells where a calcium increase was detected, the response was very small and slow to peak. In contrast, the same concentration of InsP₃ resulted in large and rapidly rising calcium responses in all acutely dissociated Purkinje cells tested. Similar to InsP₃, caffeine also had little effect on calcium levels in cultured Purkinje cells, yet evoked large calcium transients in all acutely dissociated Purkinje cells tested. The results demonstrate that calcium release from intracellular calcium stores is severely impaired in Purkinje cells when they are maintained in culture. Our findings suggest that cultured Purkinje cells are an unfaithful experimental model for the study of the role of calcium release in the induction of cerebellar long term depression.