The calcium-dependent slow after-hyperpolarization in myenteric plexus neurones with tetrodotoxin-resistant action potentials.

Intracellular recordings were made from neurones of the myenteric plexus of the guinea-pig ileum. The slow after-hyperpolarization which followed an action potential in some neurones was abolished by Mn(++), La(+++) and by solutions which contained no Ca(++). In these neurones, the action potential and the slow after-hyperpolarization persisted in Na(+)-free solutions or in the presence of tetrodotoxin (2 muM). The findings suggest that an inward Ca(++) current during the action potential is essential for the slow after-hyperpolarization.