Abstract
Growth cones of isolated neuron 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 μM), 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 GTPγS and Gpp(NH)p caused FMRFamide's effect to become irreversible. Dialysis with GDPβS 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.
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