Figure 5.

Regulation of the inward Ca²⁺ current. (A) Effect of internal Ca²⁺ concentration on Ca²⁺ currents at the tip of young hairs. Whole-cell currents were recorded in the presence of 10 mM external BaCl₂ and 10, 100, or 900 nM internal free Ca²⁺ [free Ca²⁺ controlled with 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetate]. Three successive recordings were performed 30, 40, and 50 min after whole-cell attainment and averaged for each spheroplast examined. (B–E) Comparison of Ca²⁺ currents in growing and nongrowing regions. Typical example of current traces in spheroplasts from the tip of a young hair (growth rate ≅ 1 μm⋅min⁻¹) (B), from the tip of a “nongrowing” hair (growth < 0.2 μm⋅min⁻¹) (C), and from subapical regions (D). Currents were recorded in the presence of 10 mM external BaCl₂ and 100 nM internal free Ca²⁺. (E) Mean ± SEM I–V relationships for the three regions. Recordings from mature hairs and subapical regions were obtained in the same conditions as those from tips of young hairs (similar time after spheroplast release, same time after whole-cell attainment).