α-Latrotoxin forms calcium-permeable membrane pores via interactions with latrophilin or neurexin

In order to explore the mechanisms by which alpha -latrotoxin activates neurotransmitter release, we have characterized its effects by patch-clamp methods on cells heterologously expressing its receptors, latrophilin-1 or neurexin-I alpha. Application of alpha -latrotoxin (1 nm) to cells expressing rat latrophilin or neurexin, but not mock-transfected cells, induced a cationic conductance. In cells expressing latrophilin, current development was slow in the absence of divalent cations, but was accelerated by Ca2+ or Mg2+. In cells expressing neurexin, alpha -latrotoxin did not elicit currents in the absence of Ca2+. The toxin-induced conductance was rectifying, persistent, permeable to monovalent and divalent cations, but blocked by La3+. Single-channel recording revealed a permanently open state, with the same unitary conductance irrespective of whether cells expressed latrophilin or neurexin. Therefore, while pore formation displayed differences consistent with the reported properties of alpha -latrotoxin binding to latrophilin and neurexin, the pores induced by alpha -latrotoxin had identical properties. These results suggest that after anchoring to either of its nerve terminal receptors, alpha -latrotoxin inserts into the membrane and constitutes a single type of transmembrane ion pore.