Delayed appearance of G-protein coupled signal transduction system in developing cerebellar Purkinje cell dendrites

To investigate the relation between the function of Ca²⁺-activated K⁺ channels and phosphoinositide turnover, we have examined the physiological and pharmacological characteristics of ionotropic and metabotropic quisqualate (QA) receptors in rat cerebellar Purkinje cells during development using the slice-patch method combined with Ca²⁺ imaging. The typical response to QA obtained from a rat on postnatal day (PND) 21 consisted of three components: (1) a fast inactivating inward current, (2) a slow inward current, and (3) a slow outward current. The slow inward current was abolished in Ca²⁺-free medium, while the fast inactivating inward current and the slow outward current remained unaffected. The slow outward current which appeared to be activated via a metabotropic receptor was not observed in the Purkinje cell of PND 7 rat, in which dendrites were poorly developed but its amplitude increased linearly with PND. QA caused significant increases in [Ca²⁺]_i in the fully developed dendritic region of the Purkinje cells even in Ca²⁺-free medium, suggesting a dendritic localization of the metabotropic receptors.