However, in all animals with nervous systems, neurons generate action potentials (APs), release excitatory and inhibitory neurotransmitters, form circuits, receive sensory input, innervate muscle, and direct behavior.
Voltage-gated ion channels are the basis of electrical excitability of all animals and many single-celled eukaryotes. Potassium leak and voltage-dependent K+ (Kv) channels appeared three billion years ago in bacteria and occur in all organisms (11) (Fig. 1).
They establish resting potentials and repolarize membranes after excitatory events.
The three main types of Cav channels are L, N/P/Q/R, and T. Generally speaking, L type channels are found in muscle and neuronal dendrites, and N/P/Q/R are found in synaptic terminals and regulate transmitter release, whereas T types, which are sensitive to voltages close to resting potential, underlie spontaneous firing and pacemaking.
The presence of a K in domain III of the pore, as in the bilaterian Nav1, increases Na+ selectivity substantially (Fig. 3)
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