Light-induced changes of extracellular volume in a planarian ocellus

A planarian ocellus attached to a small amount of associated tissues was superfused with planarian physiological solution containing tetramethylammonium (TMA(+)) as a probe cation. The extracellular activity of TMA(+) ([TMA(+)](o)) in the ocellus was measured with a double-barreled ion-selective microelectrode. In some experiments, alpha-naphthalene sulfonate was used as a probe anion. [TMA(+)](o) increased by 1% or less of initial dark activity under a 0.5-sec light flash and by about 7% during long-term illumination (60 sec). This result indicates that the extracellular volume of the planarian ocellus decreases during light exposure. (C) 1997 Elsevier Science Inc.