Motoneuronal after-potentials and extracellular divalent cations.

In cats under Dial anesthesia, microiontophoretic injections of Co2+ or Mn2+ outside lumbosacral motoneurones regularly diminish the postspike hyperpolarizing after-potential (AHP) without any clear reduction of the deplorarizing after-potential (ADP). Comparable injections of Sr2+ have the opposite effect of augmenting the AHP. These results indicate that the AHP is indeed initiated by an influx of calcium linked to the action potential, but the ADP is unlikely to be mainly a manifestation of a calcium inward current.