Figure 4.

Effects of β-neuregulin on large-conductance K⁺ channels in developing CG neurons. (A) Inside–out patch recording from E9 neuron cultured for 12 hr in the absence of trophic factor. Traces to the left show large-conductance K⁺ channels in Ca²⁺-free saline (Upper Left) and in saline with free Ca²⁺ buffered to approximately 10 μM (Lower Left). Membrane potential is −60 mV. Note that gating of large-conductance channels is essentially independent of free Ca²⁺ concentration. These large-conductance channels reverse close to the calculated E_K (+17 mV) and have a unitary slope conductance of 285 pS (Right). (B) Inside–out patch from E9 CG neuron cultured for 12 hr with 1 nM β-neuregulin peptide. Patch is quiescent in Ca²⁺-free saline (Upper Left), but large-conductance channels exhibit high level of activity in the presence of saline containing 10 μM free Ca²⁺ (Lower Left). Membrane potential is −60 mV. These large-conductance channels reverse close to calculated E_K and have a unitary slope conductance of 285 pS (Right).