RESPONSIVENESS TO ATP WITH AN INCREASE IN INTRACELLULAR FREE CA2-D-28IMMUNOREACTIVE NEURONS IN MYENTERIC GANGLIA( IS NOT A DISTINCTIVE FEATURE OF CALBINDIN)

The aim of this study was to test the hypothesis that ATP elevates cyt osolic free Ca2+ levels ([Ca2+](i)) in myenteric neurons expressing th e Ca2+ binding protein, calbindin-D-28. A Laser microbeam marked the l ocation of cultured neurons on coverslips and provided unequivocal rel ocation of ATP-responsive neurons after immunocytochemistry. All myent eric multipolar neurons displayed ATP Ca2+ transients, and 42% also ex pressed calbindin-D-28 reactivity. Statistical analysis of the kinetic s and shape of ATP Ca2+ transients revealed no differences between cal bindin and non-calbindin neurons. The identity of other responsive neu rons is unknown. Less than 8% of ganglion cells with ATP Ca2+ transien ts were immunopositive for the glial protein S-100. We conclude that o ne of the actions of ATP in myenteric ganglia is to increase [Ca2+](i) which may activate gK(Ca) leading to membrane hyperpolarization in AH , Dogiel Type II neurons expressing calbindin-D-28. An efficient buffe ring mechanism for handling large purinergic Ca2+ loads is a common fe ature of all types of myenteric ganglion cells.