Measurement of the intracellular calcium concentration in guinea-pig myenteric neurons by using fura-2.

Intracellular free calcium concentration [( Ca2+]i) was measured in guinea-pig myenteric neurons by using the fluorescent calcium indicator, fura-2; at the same time, intracellular recordings were made from the myenteric neurons. The [Ca2+]i of the myenteric neurons was about 100 nM at the resting state. The slow after-hyperpolarization that followed an action potential was associated with an increase in [Ca2+]i [Ca2+]i decreased during superfusion with calcium-free/high (6 mM) magnesium solution, and increased during superfusion with high (20 mM) potassium solution. However, [Ca2+]i did not change when the depolarizations caused in the high potassium solution were prevented by passing inward current through the recording electrode. The present experiments provide direct evidence that depolarization of the myenteric neurons allows calcium to enter the cell, and that rises in intracellular calcium concentration hyperpolarize the neuron.