Figure 2.

Permeability of CRAC channels to organic cations. CRAC channels were activated during whole-cell dialysis with Na⁺ aspartate. The external solution contained 1 μM Ca²⁺ and 150 mM X⁺, where X⁺ is ammonium (A and B), methylammonium (C), dimethylammonium (D), trimethylammonium (E), tetramethylammonium (F and J), ethylammonium (G), isopropylammonium (H), and NMDG⁺ (I and J). Most panels illustrate currents using voltage ramps as in Fig. 1; note that the current amplitude scales vary. For these panels, three ramp traces show, including one before activation of CRAC channels, Ca²⁺ currents through CRAC channels with 20 mM [Ca²⁺]_o, and monovalent currents upon lowering [Ca²⁺]_o to 1 μM. (B and J) Current amplitudes at −80 and +30 mV before and after changing the bath solution from 20 mM Ca²⁺ to 1 μM Ca²⁺ containing ammonium (B) or TMA⁺ followed by NMDG⁺ (J). The bars above the current correspond to the main external cation. Note that the NH₄ ⁺ currents are sustained in B. In I and J, there are no detectable inward currents carried by NMDG⁺. TMA⁺ carries a small but detectable inward current (F and J).