Relative potencies of metal ions on transmitter release at mouse motor nerve terminals

1. The effects of a range of metal ions were systematically studied at the mouse neuromuscular junction in order to investigate the type of calcium channel present at the nerve terminal. 2. Endplate potentials and miniature endplate potentials were recorded from the phrenic nerve diaphragm muscle preparation with glass microelectrodes. 3. Endplate potential amplitudes and quantal contents were reduced by manganese (IC50 220 microM), cadmium (IC50 11 microM), cobalt (IC50 350 microM), and nickel (IC50 420 microM). Miniature endplate potentials were not affected by these ions at concentrations equal to the IC50s. Gadolinium did not reduce endplate potentials up to 100 microM. 4. Comparisons made with known channel types in neuroblastoma cell lines suggest that the calcium channels at the motor nerve terminal are different from those types studied in the cell lines, although most similarity is shown to the high-voltage activated calcium channel types.