Diacylglycerol-mediated regulation of Aplysia bag cell neuron excitability requires protein kinase C

Abstract

Following synaptic input, the bag cell neurons of Aplysia undergo a long-term afterdischarge of action potentials to secrete egg-laying hormone and initiate reproduction. Early in the afterdischarge, phospholipase C (PLC) hydrolyzes phosphatidylinositol-4,5-bisphosphate into inositol triphosphate (IP₃) and diacylglycerol (DAG). In Aplysia, little is known about the action of DAG, or any interaction with IP₃; thus, we examined the effects of a synthetic DAG analogue, 1-oleoyl-2-acetyl-sn-glycerol (OAG), on whole-cell voltage-clamped cultured bag cell neurons. OAG induced a large, prolonged, Ca²⁺-permeable, concentration-dependent inward current (I_OAG) that reversed at ∼-20 mV and was enhanced by intracellular IP₃. A similar current was evoked by either another DAG analogue, 1,2-dioctanoyl-sn-glycerol (DOG), or activating PLC with N-(3-trifluoromethylphenyl)-2,4,6-trimethylbenzenesulfonamide (m-3M3FBS). I_OAG was reduced by the general cation channel blockers, Gd³⁺ or flufenamic acid. Work in other systems indicated that OAG activates channels independent of protein kinase C (PKC); however, we found pretreating bag cell neurons with any of the PKC inhibitors, bisindolylmaleimide, sphinganine, or H7, attenuated I_OAG. But, stimulating PKC with phorbol 12-myristate 13-acetate (PMA), did not evoke current or enhance I_OAG; moreover, unlike PMA, OAG failed to trigger PKC, as confirmed by an independent bioassay. Finally, OAG or m-3M3FBS depolarized cultured neurons, and while OAG did not provoke afterdischarges from bag cell neurons in the nervous system, it did double the duration of synaptically elicited afterdischarges. To our knowledge, this is the first report of obligate PKC activity for I_OAG gating. An interaction between phosphoinositol metabolites and PKC could control the cation channel to influence afterdischarge duration.

This article is protected by copyright. All rights reserved

from #MedicinebyAlexandrosSfakianakis via xlomafota13 on Inoreader http://ift.tt/1WGcrjq
via IFTTT