Dentate Granule Cell Capacitance Is Stable across the Light/Dark Cycle.

The plasma membrane acts as a capacitor that plays a critical role in neuronal excitability and signal propagation. Neuronal capacitance is proportional to the area of the cell membrane; thus it is often used as a measure of the cell size that is assumed to be relatively stable. Recent work proposes that the capacitance of dentate granule cells (dGCs) and cortical pyramidal cells changes across the light/dark (LD) cycle in a manner that alters synaptic integration. We addressed this potential change in capacitance using a large dataset of dGC recordings from adult male and female mice across the light cycle. Our data show that daily changes in the membrane time constant result from fluctuation in membrane resistance rather than capacitance. We also confirm the ability to resolve changes in neuronal capacitance induced by altering dGC membrane area via acute axotomy or genetically induced overgrowth using either voltage-clamp or current-clamp approaches. Our results demonstrate that the capacitance of dGCs remains stable over the LD cycle and that daily changes in the membrane time constant and excitability are mediated by fluctuations in membrane resistance.