Light-induced changes in extracellular volume in the retina of the drone, Apis mellifera.

Slices of drone retina were superfused with a Ringer solution containing 1 mM tetraethylammonium (TEA), and the concentration of this ion in the extracellular space [( TEA]0) was measured with ion-sensitive microelectrodes. A train of light flashes for 90 s caused [TEA] to increase by 48 +/- 4% (S.E.), n = 12. Since water crosses cell membranes more readily than TEA does this indicates a volume decrease of at least 32%. Measurements of Ca2+ activity under similar conditions showed an increase of 32 +/- 4% (S.E.), n = 14. Since this is less than the increase in [TEA]0 it suggests that the total amount of Ca2+ in the extracellular space actually decreased.