REGULATORY VOLUME DECREASE IN NEURONS OF APLYSIA-BRASILIANA

Aplysia brasiliana is an osmoconforming mollusc; the osmolality of its extracellular fluid follows that of the external media. This investig ation analyzes the volume changes of isolated neuron bodies exposed to hypotonic shocks. The abdominal ganglion was isolated, and the volume s of neuron bodies as well as intracellular K+ concentration were meas ured. Hypotonic shocks induce a rapid swelling followed by a slower re storation of cell volume. The regulatory volume decrease (RVD) restore s cell volume to its control value. Ba2+ slows RVD without blocking it . Furosemide (in the mu M range) completely and reversibly blocks the regulatory volume decrease. On return to isotonic solution after RVD, cell shrinkage was only detected when furosemide was present. It is co ncluded that neuron bodies of A. brasiliana display efficient processe s for volume regulation, based on a conductive pathway and a furosemid e-sensitive transport mechanism, which is probably the Na-2Cl-K cotran sporter. A model simulation provides additional support to this hypoth esis. (C) 1995 Wiley-Liss, Inc.