title: PKC enhances the capacity for secretion by rapidly recruiting covert voltage-gated Ca2+ channels to the membrane.
abstract: It is unknown whether neurons can dynamically control the capacity for secretion by promptly changing the number of plasma membrane voltage-gated Ca(2+) channels. To address this, we studied peptide release from the bag cell neurons of Aplysia californica, which initiate reproduction by secreting hormone during an afterdischarge. This burst engages protein kinase C (PKC) to trigger the insertion of a covert Ca(2+) channel, Apl Cav2, alongside a basal channel, Apl Cav1. The significance of Apl Cav2 recruitment to secretion remains undetermined; therefore, we used capacitance tracking to assay secretion, along with Ca(2+) imaging and Ca(2+) current measurements, from cultured bag cell neurons under whole-cell voltage-clamp. Activating PKC with the phorbol ester, PMA, enhanced Ca(2+) entry, and potentiated stimulus-evoked secretion. This relied on channel insertion, as it was occluded by preventing Apl Cav2 engagement with prior whole-cell dialysis or the cytoskeletal toxin, latrunculin B. Channel insertion reduced the stimulus duration and/or frequency required to initiate secretion and strengthened excitation-secretion coupling, indicating that Apl Cav2 accesses peptide release more readily than Apl Cav1. The coupling of Apl Cav2 to secretion also changed with behavioral state, as Apl Cav2 failed to evoke secretion in silent neurons from reproductively inactive animals. Finally, PKC also acted secondarily to enhance prolonged exocytosis triggered by mitochondrial Ca(2+) release. Collectively, our results suggest that bag cell neurons dynamically elevate Ca(2+) channel abundance in the membrane to ensure adequate secretion during the afterdischarge.
authors: Department of Biomedical and Molecular Sciences, Physiology Graduate Program, Queen's University, Kingston, Ontario K7L3N6, Canada.
authors: Christopher J
authors: CJ
authors: Groten
authors: Department of Biomedical and Molecular Sciences, Physiology Graduate Program, Queen's University, Kingston, Ontario K7L3N6, Canada magoski@queensu.ca.
authors: Neil S
authors: NS
authors: Magoski
mesh_terms: D000199:Actins / Q000187:drug effects; D000818:Animals; D001048:Aplysia / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D003599:Cytoskeleton / Q000187:drug effects; D004789:Enzyme Activation / Q000502:physiology; D005089:Exocytosis / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011493:Protein Kinase C / Q000502:physiology*; D011999:Recruitment, Neurophysiological; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D000199:Actins; D015220:Calcium Channels; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium
keywords: Aplysia; Ca2+ channel insertion; PMA; bag cell neurons; mitochondria; peptide secretion