THE EFFECTS OF LYOTROPIC ANIONS ON ELECTRIC-FIELD-INDUCED GUIDANCE OFCULTURED FROG NERVES

1. Dissociated Xenopus neurites turn cathodally in small applied elect ric fields. Increasing the external polycation concentration alters th e direction and extent of field-induced orientation. A decrease in mem brane surface charge may underlie these effects. 2. Lyotropic anions i ncrease membrane surface charge and we have examined the effect of per chlorate (ClO4-), thiocyanate (SCN-) and sulphate (SO42-) on galvanic nerve orientation. 3. Perchlorate and SCN- had no effect on field-indu ced cathodal turning, whereas incubation with SO42- was inhibitory. In addition to its effects on surface charge, SO42- increases production of the second messengers diacylglycerol and inositol trisphosphate. I nterestingly, lithium (Li+), a blocker of polyphosphoinositide metabol ism, had a similar effect to SO42- on field-induced neurite orientatio n. 4. We conclude that increasing surface charge with lyotropic anions neither enhances galvanotropic orientation nor underlies the inhibito ry effects of SO42- and suggest that modulation of galvanotropism by S O42- occurs owing to changes in the inositolphospholipid second messen ger system.