The effects of lyotropic anions on electric field-induced guidance of cultured frog nerves.

1. Dissociated Xenopus neurites turn cathodally in small applied electric fields. Increasing the external polycation concentration alters the direction and extent of field-induced orientation. A decrease in membrane surface charge may underlie these effects. 2. Lyotropic anions increase membrane surface charge and we have examined the effect of perchlorate (ClO4-), thiocyanate (SCN-) and sulphate (SO4(2-)) on galvanic nerve orientation. 3. Perchlorate and SCN- had no effect on field-induced cathodal turning, whereas incubation with SO4(2-) was inhibitory. In addition to its effects on surface charge, SO4(2-) increases production of the second messengers diacylglycerol and inositol trisphosphate. Interestingly, lithium (Li+), a blocker of polyphosphoinositide metabolism, had a similar effect to SO4(2-) on field-induced neurite orientation. 4. We conclude that increasing surface charge with lyotropic anions neither enhances galvanotropic orientation nor underlies the inhibitory effects of SO4(2-) and suggest that modulation of galvanotropism by SO4(2-) occurs owing to changes in the inositolphospholipid second messenger system.