An eye-specific G beta subunit essential for termination of the phototransduction cascade.

Heterotrimeric G proteins couple various receptors to intracellular effector molecules. Although the role of the G alpha subunit in effector activation, guanine nucleotide exchange and GTP hydrolysis has been well studied, the cellular functions of the G beta subunits are less well understood. G beta gamma dimers bind G alpha subunits and anchor them to the membrane for presentation to the receptor.

Microinjection of the alpha-subunit of the G protein Go2, but not Go1, reduces a voltage-sensitive calcium current.

Calcium currents can be modulated by receptor activation of the GTP-binding protein G(o). We have determined whether the two forms of G(o), Go1 and Go2, differentially regulate calcium current magnitude. Using identified neurons of the pond snail Helisoma, we demonstrate that a high-voltage-activated (HVA) calcium current is reduced by addition of the neuropeptide Phe-Met-Arg-Phe-amide (FMRFamide) and that this inhibition is mediated by a pertussis toxin (PTX)-sensitive G protein pathway.

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.

FMRFamide modulation of secretory machinery underlying presynaptic inhibition of synaptic transmission requires a pertussis toxin-sensitive G-protein.

The neuropeptide FMRFamide modulates synaptic transmission between identified neurons of the pond snail Helisoma trivolvis. FMRFamide causes a presynaptic inhibition of transmitter release by actions on ion channels and secretory machinery (Man-Son-Hing et al., 1989).

A relation between synaptic specificity and the acquisition of presynaptic properties.

1. The specificity of synaptogenesis of identified adult neurons of Helisoma was determined in cell culture. Cholinergic neuron B5 indiscriminately forms the presynaptic element of chemical connections with novel cholinoceptive target neurons and muscle.