Characterization of voltage- and Ca(2+)-activated K+ channels in squid olfactory receptor neurons.

We performed whole-cell voltage-clamp experiments on isolated olfactory neurons from the squid Lolliguncula brevis. Total outward currents were composed of three identifiable K+ currents: a delayed rectifier K+ current that showed slow inactivation and was sensitive to 5 mmol l-1 tetraethylammonium; a rapidly inactivating, 4-aminopyridine (4-AP)-sensitive, A-type K+ current and a Ca(2+)-sensitive K+ current that was blocked by 200 nmol l-1 charybdotoxin and 10 mmol l-1 Cd2+ but was insensitive to apamin. The proportion of each current type varied from cell to cell, suggesting that responses to a given odorant would depend of the complement of channels present. The kinetics of the K+ currents were affected by temperature, with Q10 values ranging from 2 to 6. The identification and characterization of these K+ currents will greatly aid our understanding of action potential generation in these cells and will facilitate modelling of how odor responses are transduced and coded in squid olfactory receptor neurons.