Figure 12. Effects of osmotic stress on ACh-evoked exocytotic events.

A, hyposmotic stress (-100 mosmol l⁻¹). Hyposmotic stress (•) was applied by reducing the NaCl concentration of the control solution by 50 mM. Application of hyposmotic stress did not cause the frequency of exocytotic events to increase in the absence of ACh. ACh at 1 μM stimulated exocytotic events. The frequency of exocytotic events evoked by ACh during 5 min stimulation was higher in hyposmotic experiments than in isosmotic experiments (○), but the time course was similar in the two experiments. B, hyperosmotic stress (+100 mosmol l⁻¹). Hyperosmotic stress (•) was applied by adding 50 mM NaCl to the control solution. Application of hyperosmotic stress did not cause the frequency of exocytotic events to increase in the absence of ACh. ACh at 1 μM stimulated exocytotic events. The frequency of exocytotic events evoked by ACh during 5 min stimulation was higher in hyperosmotic experiments than in isosmotic experiments (○), and the time course of the increases in the frequency of exocytotic events was different in hyperosmotic experiments from that in isosmotic or hyposmotic experiments. The time to reach the peak value was delayed from 1 to 2.5 min after the start of ACh stimulation.