The leaner P/Q-type calcium channel mutation renders cerebellar Purkinje neurons hyper-excitable and eliminates Ca(2+)-Na(+) spike bursts.

摘要

The leaner mouse mutation of the Cacna1a gene leads to a reduction in P-type Ca(2+) current, the dominant Ca(2+) current in Purkinje cells (PCs). Here, we compare the electro-responsiveness and structure of PCs from age-matched leaner and wild-type (WT) mice in pharmacological isolation from synaptic inputs in cerebellar slices. We report that compared with WT, leaner PCs exhibit lower current threshold for Na(+) spike firing, larger subthreshold membrane depolarization, rapid adaptation followed by complete block of Na(+) spikes upon strong depolarization, and fail to generate Ca(2+)-Na(+) spike bursts. The Na(+) spike waveforms in leaner PCs have slower kinetics, reduced spike amplitude and afterhyperpolarization. We show that a deficit in the P-type Ca(2+) current caused by the leaner mutation accounts for most but not all of the changes in mutant PC electro-responsiveness. The selective P-type Ca(2+) channel blocker, omega-agatoxin-IVA, eliminated differences in subthreshold membrane depolarization, adaptation of Na(+) spikes upon strong current-pulse stimuli, Na(+) spike waveforms and Ca(2+)-Na(+) burst activity. In contrast, a lower current threshold for eliciting repetitive Na(+) spikes in leaner PCs was still observed after blockade of the P-type Ca(2+) current, suggesting secondary effects of the mutation that render PCs hyper-excitable. Higher input resistance, reduced whole-cell capacitance and smaller dendritic size accompanied the enhanced excitability in leaner PCs, indicative of developmental retardation in these cells caused by P/Q-type Ca(2+) channel malfunction. Our data indicate that a deficit in P-type Ca(2+) current leads to complex functional and structural changes in PCs, impairing their intrinsic and integrative properties.