Voltage-gated calcium channels(VGCCs)control a plethora of physiological processes,from muscle contraction,heartbeat,neural communication and hormone secretion to cell differentiation,motility,growth and apoptosis.Their mutations and dysfunction are linked to diverse disorders such as epilepsy,migraine,ataxia,hypertension,arrhythmia,and autism.To serve their vital and varying roles,VGCCs are subject to tight regulation by diverse pathways and mechanisms.We have uncovered a novel age-dependent proteolysis that profoundly affects the activity of VGCCs.Using biochemical and imaging approaches,we find that the main body(i.e.,the four homologous internal repeats and the tethering cytosolic linkers)of the pore-forming α1 subunit of neuronal L-type VGCCs,Cav1.2,is proteolytically cleaved,resulting in Cav1.2 fragment-channels that separate but remain on the plasma membrane.This midchannel proteolysis is regulated by intracellular calcium and L-type channel activity,involves the Ca2+-dependent protease calpain and the ubiquitin-proteasome system,and causes attenuation and biophysical alterations of VGCC currents.Recombinant Cav1.2 fragment-channels mimicking the products of mid-channel proteolysis do not form active channels on their own,but when properly paired,produce currents with distinct biophysical properties.Fragment-channels also interact with full-length Cav1.2 and alter the properties of full-length channels.In a mammalian model system,midchannel proteolysis increases dramatically with age and can be attenuated by an L-type VGCC blocker in vivo.Midchannel proteolysis represents a novel form of homeostatic negative-feedback processing of VGCCs that could profoundly affect neuronal excitability,neurotransmission,neuroprotection and calcium signaling in physiological and disease states.