Effect of new O-superfamily conotoxin on voltage-activated currents of hippocampal neurons

The effects of a new O-superfamily conotoxin, S03, on sodium current (I
Na
), transient A-type potassium currents (I
A
), and delayed rectified potassium currents (I
K
), were examined in cultured rat hippocampal neurons using the whole-cell patch clamp technique. Addition of S03 caused a concentration-dependent, rapidly developing, and reversible inhibition of voltage-activated currents. The IC
50
values for the blockage of I
Na
, I
A
; and I
K
were calculated as 0.49, 33.9, and 7.6 μmol/l., respectively. The determined Hill coefficients were 1.7, 0.6, and 1.2, respectively. These results indicate that S03 can selectively inhibit neuronal sodium and potassium currents.