Summary of Session and Discussion on Electrical Excitability
The papers of the day showed that modern protists have many of the features needed for making neurons. In particular, they have a wide variety of voltage-gated Ca++ and K+ channels that are functionally very similar to those of neurons and they have several kinds of mechanoreceptive channels. Protists respond sensitively to chemicals and to touch. They can conduct Ca++ spikes and coordinate motor outputs with the underlying Ca++ fluxes. Actinocoryne makes a Na+/Ca++ spike. They have receptors coupled to GTP-binding proteins. However, no channel that gates open within milliseconds of binding a ligand (such as is found in fast chemical synapses) has been reported in protists.