affinity of the channel for the penetrating ions of alkali-earth metals decreases in the sequence : mg2+ greater than ca2+ greater than sr2+ approximately equal to ba2+ and the blocking ability of the cations of transition metals increases in the series : mn2+ less than zn2+ approximately less than ni2+ approximately less than co2+ less than cd2+ much less than la3+ .
C0022023
ions
C0007447
cations