Isolation and characterization of a fraction from brain that inhibits 1,4-[ 3H]dihydropyridine binding and L-type calcium channel current

Bovine brain was subjected to acid extraction and several purification steps. A fraction from brain that eluted from C18 reverse-phase columns at 30–35% acetonitrile inhibited [ 3H]nitrendipine binding to cardiac membranes. Further purification of this fraction on a sizing column in the presence of 40% acetonitrile yielded a low molecular mass fraction (< 1 kDa) that produced a time- and voltage-dependent inhibition of L-type (but not T-type) Ca 2+-channel current in GH 3 cells. The results suggest that this fraction contains an endogenous substance that binds directly to slowly-inactivating Ca 2+ channels and thereby inhibits current flow.