EFFECTS OF CHRONIC EXPOSURE TO CADMIUM-ENRICHED OR LEAD-ENRICHED ENVIRONMENTS ON IONIC CURRENTS OF IDENTIFIED NEURONS IN LYMNAEA-STAGNALIS L

1. Voltage-activated ionic currents of three identified neurons of Lym naea stagnalis L. were compared in control snails and in animals havin g been exposed to a cadmium- or lead-enriched environment for 2 weeks. We determined the presence, amplitude, and changes, if any, in the cu rrent-voltage characteristics of calcium and potassium currents in eac h of the three neurons from each of the three groups of animals. Final ly, we have compared the effects of acute administration of Cd2+ or Pb 2+ on neurons from control and chronically exposed animals. 2. Chronic exposure to cadmium resulted in a near doubling of the high voltage-a ctivated calcium current. 3. No differences were found in the effects of acute application of Cd2+ or Pb2+ on neurons of pretreated and cont rol animals. Cadmium was a potent blocker of the Ca current in either case, while lead caused only a 20% inhibition of the Ca current in neu rons of both control and lead-exposed animals. 4. Potassium currents w ere affected in both Cd2+- and Pb2+-exposed animals. While the sustain ed outward current was not influenced noticeably, the fast K current w as affected in different ways in different neurons. Some did not show this current in the controls but expressed it in neurons from the expo sed animals. Other neurons showed the current in the controls and its depression in exposed animals. Acute application of cadmium did not mo dulate the K current, but lead enhanced the peak amplitude of the tran sient K current in neurons of both exposed and control snails.