Figure 6. Role of extracellular [Ca²⁺] and the spider GsMTx-4 toxin in the activation of calpain by hypo-osmotic shock.

A, calpain activity was measured in resting conditions (average taken as 100%, dashed horizontal line) or after 10 min incubation in a hypo-osmotic solution containing 15 mm (n = 8), 1.5 mm (n = 5) or 0.1 mm[Ca²⁺]_o (n = 8), or in the absence of [Ca²⁺]_o (1 mm EGTA, n = 5). B, the effect of 5 μm GsMTx-4 was also tested in the presence of 1.5 mm[Ca²⁺]_o (n = 6). *Significantly different from control conditions (P < 0.05), paired Student's t test.