FIGURE 1.

Defining properties of Ca²⁺ and ATP-sensitive nonselective cation channels (CA-NSCs) in rat brain endothelial cells. (A) A single CA-NSC channel, silent in the cell-attached mode, is activated by excision (arrow) into a high-Ca²⁺ bath solution. The channel is immediately and reversibly shut by superfusion with either Ca²⁺-free solution (1 mM EGTA), or with 1 mM MgATP or Na-flufenamate. (B) Single-channel current-voltage plots and fits under three ionic conditions obtained from a single patch. Pipette solution was NaCl-based (140 mM) in all three cases, while bath solution contained 140 mM KCl (▾), NaCl (▵), or NMG-Cl (•). Straight-line fits to the plots for the KCl-and NaCl-based bath yielded slope-conductances and reversal potentials of 29 ± 1 pS, −7 ± 2 mV, and 26 ± 1 pS, −2 ± 1 mV, respectively. In the case of the NMG-Cl-based bath the plot was fitted with the G-H-K current equation yielding an asymptotic slope conductance of 29 ± 1 pS at very negative voltages (Methods), and a reversal potential of +72 mV. (C) Single-channel current-voltage plot with 90 mM CaCl₂ in the pipette and 144 mM Na⁺ in the bath. A fit to the G-H-K current equation (solid line) assuming zero permeability for Ca²⁺ yielded an asymptotic slope conductance at very positive voltages of 13 ± 0.1 pS (see Methods). A straight-line fit (dotted line) predicted a reversal potential of −45 ± 4 mV.