INHIBITION OF CALCIUM SPIKES BY GAMMA-AMINOBUTYRIC-ACID IN THE NEURONS OF LYMNAEA-STAGNALIS L

The modulation of action potentials (APs) and high-threshold calcium c urrents by gamma-aminobutyric acid (GABA) and GABA(B) receptor agonist baclofen was investigated in identified internally perfused neurons o f Lymnaea stagnalis using current-clamp and whole-cell voltage-clamp t echniques. GABA (5 x 10(-5) M) and baclofen (5 x 10(-5) M) reversibly reduced overshoot and afterhyperpolarization phase of the action poten tials. Application of GABA or baclofen inhibited inward and outward vo ltage-gated ionic currents. GABA (10(-8)-10(-4) M) was found to suppre ss high-threshold calcium current in voltage- ard dose-dependent manne r. These effects were mimicked by baclofen (5 x 10(-5) M) but not by m uscimol (5 x 10(-5) M). Inhibition of Ca2+-currents could not be preve nted by pentylenetetrazole (5 x 10(-5) M) or with pertussis toxin (1 m u g/ml). These results provide evidences for the presence of GABA(B) r eceptors in the identified central neurons of Lymnaea stagnalis L.