Figure 3.

Maitotoxin-induced extracellular Ca²⁺-dependent voltage-insensitive Ca²⁺ influx. (I) Extracellular Ca²⁺ dependence of maitotoxin-induced Ca²⁺ influx in C6-BU-1 cells. [Ca²⁺]_i was measured as described in Methods. The cells loaded with fura 2 acetoxy methylester were suspended in the Tyrode solution. (a) Maitotoxin (MTX, 10 ng ml⁻¹) was added 90 s after addition of 1 mM Ca²⁺ (control for b and c). (b) Maitotoxin (MTX, 10 ng ml⁻¹) was added 90 s after addition of 5 mM Mg²⁺ and 1 mM Ca²⁺. (c) Maitotoxin (MTX, 10 ng ml⁻¹) was added after addition of 5 mM EGTA in the presence of 1 mM Ca²⁺. (II) Maitotoxin-induced Ca²⁺ influx through voltage-insensitive Ca²⁺ channel. (d) Maitotoxin (MTX, 10 ng ml⁻¹) was added 90 s after addition of 1 mM Ca²⁺ (control for e and f). (e) Maitotoxin (MTX, 10 ng ml⁻¹) was added 120 s after addition of high KCl (50 mM) in the presence of 1 mM Ca²⁺. (f) Maitotoxin (MTX, 10 ng ml⁻¹) was added 120 s after addition of high NaCl (50 mM) in the presence of 1 mM Ca²⁺.