Effects of osmotic changes in extracellular solution on electrical activity of mouse pancreatic B-cells

The influence of changes in the osmolarity of the extracellular solution on electrical activity of mouse pancreatic B-cells was studied with intracellular microelectrodes. In the presence of 15 mmol/l glucose the membrane potential of B-cells oscillates. A reduction of the osmolarity by 40 mosmol/l caused a small temporary hyperpolarization in six out of eight cells. After 2 to 3 min electrical activity was increased in all cells. However, this effect was also transient. 5 to 8 min after onset of exposure to hypotonic solution the cells repolarized again and electrical activity decreased. Increasing the osmolarity of the extracellular solution by 40 mosmol/l led to a sustained and reversible depolarization of the membrane potential. However, the electrical activity was transiently suppressed. The changes in electrical activity observed in hypotonic solution might explain the previously described transient rise in insulin secretion provoked by osmotic cell swelling.