Figure 3.

Selectivity and block of the inward Ca²⁺ current. (A–C) Whole-cell current sensitivity to increases in external BaCl₂ concentration; successively 1 (A) and 50 (B) mM. (C) Corresponding I–V curve of total current. (D) Effect of the addition of CsCl (20 mM) on Ca²⁺ current. External CaCl₂ was 10 mM; traces were obtained by hyperpolarizing the membrane to −200 mV during 1 s to activate the Ca²⁺ conductance, then slowly depolarizing (30 mV/s) up to +90 mV; each trace is the average of three successive repeats. Currents were plotted against corresponding voltages. (E–G) Comparison of whole-cell currents with external Ca²⁺ or Mn²⁺. Currents were recorded successively in 10 mM MnCl₂ (traces not shown), CaCl₂ (E), and, again, MnCl₂ (F). (G) Corresponding I–V. (H) Comparison of whole-cell currents with external Ca²⁺ or Mg²⁺. Currents were recorded successively in 10 mM CaCl₂, MgCl₂, and, again, CaCl₂; voltage-clamp protocol was similar to that in D. (I–K) Block of the Ca²⁺ current by La³⁺ (I; 25 μM), Al³⁺ (J; 50 μM), and Gd³⁺ (K; 50 μM). External CaCl₂ was 10 mM; Voltage-clamp protocols were similar to D.