Calcium-induced calcium release in cerebellar Purkinje cells.

Depolarization-induced intracellular Ca2+ rises were measured in fura-2-loaded, voltage-clamped Purkinje cells. The peak Ca2+ rise increased more than linearly with voltage step duration, suggesting the presence of Ca(2+)-induced Ca2+ release. In cells from young animals, in which Ca2+ currents could be satisfactorily recorded, a supralinear relation was also found between peak Ca2+ rise and Ca2+ current integral. Responses to long pulses were inhibited in cells dialyzed with 20 microM ruthenium red and potentiated in cells bathed in the presence of 20 microM ryanodine. Upon repetitive depolarization, increasing Ca2+ rises were elicited by successive voltage pulses, probably because of a potentiating effect of residual Ca2+. Altogether, the results indicate an important contribution of Ca(2+)-induced Ca2+ release to Ca2+ signals of Purkinje cells.