Light-Induced Changes of Extracellular Volume in a Planarian Ocellus

Abstract

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, α-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.