Figure 4.

Single-channel features of the inward-rectifying Ca²⁺ channel. (A and B) Examples of traces (A) and analysis of channel activation (B, same patch) from an outside-out patch bathed in 10 mM CaCl₂. Cl⁻ and Ca²⁺ equilibrium potentials were −77 and +150 mV (E_{Ca + Mg} = +40 mV), respectively. (A) < indicates the lowest level of current; it corresponds to zero channel open except at −136 mV, where baseline corresponds to one channel open (1). The membrane potential is indicated to the right of each trace. Holding potential was −56 mV. (B) nPo (n, number of active channels; Po, open probability) was extracted from 3-s pulses. (C–E) Examples of single-channel traces in 10 mM of either MnCl₂ (C; same patch as in A), MgCl₂ (D), or BaCl₂ (E). Holding potential was −208 mV in C, because channel activity had strongly declined in MnCl₂, −14 mV in D, and +5 mV in E. (F) Single-channel I–V relationships with 10 mM external concentration of either Ca²⁺, Mn²⁺, Mg²⁺, or Ba²⁺. Ten experiments have been pooled.