Protein kinase C gamma in cerebellar Purkinje cells regulates Ca2+-activated large-conductance K+ channels and motor coordination

The cerebellum, the site where protein kinase C (PKC) was first discovered, contains the highest amount of PKC in the central ner-vous system, with PKC gamma being the major isoform. Systemic PKC gamma-knockout (KO) mice showed impaired motor coordination and deficient pruning of surplus climbing fibers (CFs) from developing cerebellar Purkinje cells (PCs). However, the physiological significance of PKC gamma in the mature cerebellum and the cause of motor incoordination remain unknown. Using adeno-associated virus vectors targeting PCs, we showed that impaired motor coordination was restored by re-expression of PKC gamma in mature PKC gamma-KO mouse PCs in a kinase activity-dependent manner, while normal motor coordination in mature Prkcg(fl/fl) mice was impaired by the Cre-dependent removal of PKC gamma from PCs. Notably, the rescue or removal of PKC gamma from mature PKC gamma-KO or Prkcg(fl/fl) mice, respectively, did not affect the CF innervation profile of PCs, suggesting the presence of a mechanism distinct from multiple CF innervation of PCs for the motor defects in PKC gamma-deficient mice. We found marked potentiation of Ca2+-activated large-conductance K+ (BK) channel currents in PKC gamma-deficient mice, as compared to wild-type mice, which decreased the membrane resistance, resulting in attenuation of the electrical signal during the propagation and significant alterations of the complex spike waveform. These changes in PKC gamma-deficient mice were restored by the rescue of PKC gamma or pharmacological suppression of BK channels. Our results suggest that PKC gamma is a critical regulator that negatively modulates BK currents in PCs, which significantly influences PC output from the cerebellar cortex and, eventually, motor coordination.