PROPERTIES OF 185TAGE-ACTIVATED IONIC CURRENTS IN CELLS FROM THE BRAINS OF THE TRICLAD FLATWORM BDELLOURA CANDIDA

Abstract

Cells were dispersed from the brains of the triclad flatworm Bdelloura candida and maintained in primary culture for up to 2 weeks. Cultured cells assumed a variety of morphologies consistent with those of neurones in vivo. Whole-cell voltage-clamp recordings from cultured cells revealed that these cells possess a variety of ionic currents, including a fast transient sodium current, a calcium current and several potassium currents. The sodium current does not inactivate completely but instead decays to a steady-state component which has the same physiology and pharmacology as the fast transient component, suggesting that the two components are carried by the same population of channels. The physiology and pharmacology of these various currents were not remarkable save for the fact that, contrary to earlier reports, all sodium currents examined were sensitive to tetrodotoxin (TTX). These animals are, therefore, the lowest animals known to possess TTX-sensitive sodium currents and, as such, represent a major stage in sodium channel evolution.