Inhibition of synaptic transmission and G protein modulation by synthetic CaV2.2 Ca2+ channel peptides

Modulation of presynaptic voltage-dependent Ca2+ channels is a major means of controlling neurotransmitter release. TheCa(V)2.2Ca(2+) channel subunit contains several inhibitory interaction sites for G beta gamma subunits, including the amino terminal (NT) and I-II loop. The NT and I-II loop have also been proposed to undergo a G protein-gated inhibitory interaction, whilst the NT itself has also been proposed to suppress Ca(V)2 channel activity. Here, we investigate the effects of an amino terminal (Ca(V)2.2[45-55]) ` NT peptide' and a I-II loop alpha interaction domain (Ca(V)2.2[377-393]) ` AID peptide' on synaptic transmission, Ca2+ channel activity and G protein modulation in superior cervical ganglion neurones (SCGNs). Presynaptic injection of NT or AID peptide into SCGN synapses inhibited synaptic transmission and also attenuated noradrenaline-induced G proteinmodulation. In isolated SCGNs, NT and AID peptides reduced whole-cell Ca2+ current amplitude, modified voltage dependence of Ca2+ channel activation and attenuated noradrenaline-induced G protein modulation. Co-application of NT and AID peptide negated inhibitory actions. Together, these data favour direct peptide interaction with presynaptic Ca2+ channels, with effects on current amplitude and gating representing likely mechanisms responsible for inhibition of synaptic transmission. Mutations to residues reported as determinants of Ca2+ channel function within the NT peptide negated inhibitory effects on synaptic transmission, Ca2+ current amplitude and gating andGprotein modulation. Amutation within the proposed QXXER motif for G protein modulation did not abolish inhibitory effects of the AID peptide. This study suggests that the Ca(V)2.2 amino terminal and I-II loop contribute molecular determinants forCa(2+) channel function; the data favour a direct interaction of peptides with Ca2+ channels to inhibit synaptic transmission and attenuate G protein modulation.