A simple modification of the Hodgkin and Huxley equations explains type 3 excitability in squid giant axons.
Clay JR, Paydarfar D, Forger DB. A simple modification of the Hodgkin and Huxley equations explains type 3 excitability in squid giant axons. J R Soc Interface. 2008 Dec 06; 5(29):1421-8.