Modulation of growth cone calcium current is mediated by a PTX-sensitive G protein

Growth cones of isolated neurons B5 of Helisoma were voltage clamped in the whole-cell configuration. Depolarization of growth cones to -20 mV or greater activated a high-voltage-activated (HVA) calcium current. Addition of the neuropeptide FMRFamide (1 microM), which causes a presynaptic inhibition of synaptic transmission, reversibly reduced the calcium current magnitude. This inhibitory effect is mediated by a pertussis toxin (PTX)-sensitive G protein. Dialysis with the non-hydrolyzable GTP analogs GTP gamma S and Gpp(NH)p caused FMRFamide's effect to become irreversible. Dialysis with GDP beta S or preincubation with PTX prevented FMRFamide from reducing the calcium current. Thus, one role of growth cone G proteins is to modulate ion channels in growth cone membrane which in turn may control growth cone motility.