Figure 5. Effect of ACh on the cytosolic Ca²⁺ plateau in acinar cells isolated from wild-type and IP₃R KO mice.

(A) Intracellular Ca²⁺ stores of fura 2-loaded PACs, isolated from wild-type mice were depleted during a 30 min preincubation in nominally Ca²⁺-free extracellular solution containing 2 μM TG. The addition of 2 mM Ca²⁺ to the extracellular solution resulted in the formation of a [Ca²⁺]c plateau. Subsequent ACh application triggered a small drop of the plateau that could be reversed by removal of ACh. (B) Normalized (to the plateau level before ACh addition) plateau amplitude before (white bars) and following (striped bars) treatment with 50 or 300 nM ACh. Only the application of a large concentration of ACh (300 nM) caused a significant reduction of the plateau amplitude in PACs from wild-type mice (paired Student's t-test, *P<0.05). (C) Intracellular Ca²⁺ stores of fura 2-loaded PACs, isolated from IP₃R2 KO mice, were depleted with 2 μM TG in nominally Ca²⁺-free extracellular solution and subsequent addition of 2 mM Ca²⁺ resulted in the formation of a [Ca²⁺]c plateau. The application of a large concentration of ACh resulted in a small decrease in the plateau. (D) Normalized plateau amplitude, recorded from PACs from IP₃R2 KO mice, before (white bars) and following (striped bars) treatment with 50 or 300 nM ACh. Only the application of a 300 nM ACh caused a significant reduction of plateau amplitude in PACs from IP₃R2 KO mice (paired Student's t-test, * P<0.05). (E) Intracellular Ca²⁺ stores of fura 2-loaded PACs, isolated from IP₃R2/3 KO mice, were depleted as described above and a cytosolic Ca²⁺ plateau was formed by introducing 2 mM Ca²⁺ to the extracellular solution. Subsequent addition of ACh resulted in a decrease in cytosolic Ca²⁺ levels. (F) Normalized plateau amplitude, recorded from PACs from IP₃R2/3 KO mice before (white bars) and following (striped bars) treatment with 50 or 300 nM ACh. Only the application of a 300 nM ACh caused a small but statistically significant reduction of plateau amplitude (paired Student's t-test, *P< 0.05).