The role of calcium ion in the l-glutamate-induced depolarization in the frog spinal cord

Abstract

1. The role of Ca 2+ in l-glutamate-induced depolarization was investigated in the isolated frog spinal cord. 2. The size of a depolarization induced by l-glutamate (3 mM) was inversely related to the extracellular Ca 2+ concentration, but was reduced in a Ca 2+-free medium containing EGTA (0.3 mM). 3. l-Glutamate caused a marked depolarization in both ventral and dorsal roots, even in a NaCl-deficient medium (Ca 2+, 2.0 mM). The size of the depolarization was attenuated by a prolonged or repeated application of l-glutamate. Ca 2+ can be replaced by Sr 2+ or Mg 2+. 4. Concanavalin A (1 μM) prevents the development of desensitization to l-glutamate. 5. Present results suggest that Ca 2+ plays the role of a charge carrier for l-glutamate-induced depolarization and of a regulator or modulator for l-glutamate-receptor sensitivity. The roles are exaggerated in NaCl-free medium.