Alterations in the action potential of Aplysia neurons evoked by a phorbolester are mediated by protein kinase C (original) (raw)
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Long-term changes in excitability induced by protein kinase C activation in Aplysia sensory neurons
Journal of neurophysiology, 1998
Protein kinases A (PKA) and C (PKC) play a central role as intracellular transducers during simple forms of learning in Aplysia. These two proteins seem to cooperate in mediating the different forms of plasticity underlying behavioral modifications of defensive reflexes in a state- and time-dependent manner. Although short- and long-term changes in the synaptic efficacy of the connections between mechanosensory neurons and motoneurons of the reflex have been well characterized, there is also a distinct intermediate phase of plasticity that is not as well understood. Biochemical and physiological experiments have suggested a role for PKC in the induction and expression of this form of facilitation. In this report, we demonstrate that PKC activation can induce both intermediate- and long-term changes in the excitability of sensory neurons (SNs). Short application of 4beta-phorbol ester 12,13-dibutyrate (PDBU), a potent activator of PKC, produced a long-lasting increase in the number o...
Journal of Neurophysiology, 1994
1. In the pleural mechanoafferent sensory neurons of Aplysia, serotonin (5-HT)-induced spike broadening consists of at least two components: a cAMP and protein kinase A (PKA)-dependent, rapidly developing component and a protein kinase C (PKC)-dependent, slowly developing component. Voltage-clamp experiments were conducted to identify currents that are modulated by PKC and thus may contribute to the slowly developing component of 5-HT-induced spike broadening. 2. We compared the effects of phorbol esters, activators of PKC, on membrane currents with those of 5-HT. Bath application of 5-HT had complex modulatory effects on currents elicited by voltage-clamp pulses to potentials > 0 mV. The kinetics of both activation and inactivation of the membrane currents were slowed by 5-HT. This led to a decrease in an outward current at the beginning of the voltage-clamp pulse and an increase at the end of the pulse. Previous work has shown that these effects represent, in part, the modulati...
Modulation of a cAMP/protein kinase A cascade by protein kinase C in sensory neurons of Aplysia
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1997
The synaptic connections between the sensory neurons of Aplysia and their follower neurons have been used as a model system for examining the cellular mechanisms contributing to neuronal and synaptic plasticity. Recent studies suggest that at least two protein kinases, protein kinase A (PKA) and protein kinase C (PKC), contribute to serotonin (5-HT)-induced short-term facilitation. The interaction between these two kinase cascades has not been examined, however. Using electrophysiological and biochemical approaches, we examined possible interactions between PKA and PKC cascades. The results indicated that prolonged activation of PKC by preincubation with phorbol esters attenuated PKA-mediated actions of 5-HT, including increases in sensory neuron excitability and spike broadening in the presence of tetraethylammonium (TEA) and nifedipine. Although phorbol esters also attenuated increases in excitability by an analog of cAMP and small cardioactive peptide B (SCPB), the degree of atte...
Journal of Neurochemistry, 1988
Abstract: The effects of phorbol esters [phorbol 12,13-dibutyrate (PDB), 12-O-tetradecanoylphorbol 13-acetate (TPA), and phorbol 13-acetate] were investigated on the release of [3H]norepinephrine, 45Ca2+ accumulation, and protein kinase C activity in cultured sympathetic neurons of the chick embryo. Sympathetic neurons derived from 10-day-old chick embryo were cultured in serum-free medium supplemented with insulin, transferrin, and nerve growth factor. After 3 days, neurons were loaded with [3H]-norepinephrine and the release of [3H]norepinephrine was determined before and after electrical stimulation. Stimulation at 1 Hz for 15 s increased the release of [3H]-norepinephrine over the nonstimulation period. Stimulation-evoked release gradually declined with time during subsequent stimulation periods. Incubation of neurons in Ca2+-free Krebs solution containing 1 mM EGTA completely blocked stimulation-evoked release of [3H]-norepinephrine. Stimulation-evoked release of [3H]-norepinephrine was markedly facilitated by 3 and 10 nM PDB or TPA. The spontaneous release was also enhanced by PDB and TPA. The net accumulation of 45Ca2+ during stimulation of sympathetic neurons was increased by two-to fourfold in the presence of PDB or TPA. PDB at 1–100 nM produced a concentration-dependent increase in the activation of protein kinase C. PDB at 30 nM increased the activity of protein kinase C of the paniculate fraction from 0.09 to 0.58 pmol/min/mg protein. There was no significant change in protein kinase C activity of the cytosolic fraction (0.14 pmol/min/mg versus 0.13 pmol/min/mg protein). The ratio of the paniculate to cytosolic protein kinase C increased from a control value of 0.62 to 4.39 after treatment with 30 nM PDB. TPA (10 and 30 nM) also increased protein kinase C activity of the paniculate fraction by six- to eightfold. Phorbol 13-acetate had no effect on protein kinase C activity, [3H]norepinephrine release, and 45Ca2+ accumulation. These results provide direct evidence that activation of protein kinase C enhances Ca2+ accumulation, which in turn leads to the facilitation of transmitter release in sympathetic neurons.
Learning & Memory, 1994
We investigated activation of the two major neuronal protein kinase C (PKC) isoforms in Aplysia, Ca(2+)-activated Apl I and Ca(2+)-independent Apl II, during the induction and maintenance of behavioral sensitization of Aplysia defensive reflexes. Activation of PKC occurred during the training stimulus and persisted for at least 2 hr thereafter but was not maintained for 24 hr. The persistent activation required protein synthesis and was blocked by cyproheptidine, an agent that also blocked the initial activation of PKC. Persistent activation involved both an increase in membrane-associated Apl I and an increase in an autonomous kinase activity that may be related to a post-translational modification of Apl II. These results are consistent with the hypothesis that in addition to its role in producing the presynaptic facilitation of mechanosensory-motor neuron synapses that underlie short-term facilitation, PKC is needed for maintaining synaptic changes in an intermediate period that ...
Journal of Neuroscience, 2009
Under some circumstances 5-HT-dependent facilitation requires the activity of protein kinase C (PKC). One critical site of PKC's contribution to 5-HT-dependent synaptic facilitation is the presynaptic sensory neuron. Here, we provide evidence that postsynaptic PKC also contributes to synaptic facilitation. We investigated the contribution of PKC to enhancement of the glutamate-evoked potential (Glu-EP) in isolated siphon motor neurons in cell culture. A 10 min application of either 5-HT or phorbol ester, which activates PKC, produced persistent (Ͼ 50 min) enhancement of the Glu-EP. Chelerythrine and bisindolylmaleimide-1 (Bis), two inhibitors of PKC, both blocked the induction of 5-HTdependent enhancement. An inhibitor of calpain, a calcium-dependent protease, also blocked 5-HT's effect. Interestingly, whereas chelerythrine blocked maintenance of the enhancement, Bis did not. Because Bis has greater selectivity for conventional and novel isoforms of PKC than for atypical isoforms, this result implicates an atypical isoform in the maintenance of 5-HT's effect. Although induction of enhancement of the Glu-EP requires protein synthesis , we found that maintenance of the enhancement does not. Maintenance of 5-HT-dependent enhancement appears to be mediated by a PKM-type fragment generated by calpaindependent proteolysis of atypical PKC. Together, our results suggest that 5-HT treatment triggers two phases of PKC activity within the motor neuron, an early phase that may involve conventional, novel or atypical isoforms of PKC, and a later phase that selectively involves an atypical isoform.
Journal of Neurochemistry, 1988
Abstract: The effects of phorbol esters were investigated on the survival of chick sympathetic neurons in a serum-free culture medium. The protein kinase C activator phorbol 12,13-dibutyrate (PDB) supported about 40% of the plated sympathetic neurons. This number was comparable to that supported by nerve growth factor (NGF). A combination of phorbol ester and NGF did not significantly increase the number of surviving neurons. Phorbol ester-supported sympathetic neurons possessed desipramine-sensitive [3H]-norepinephrine uptake mechanism, and therefore were noradrenergic in character. Two days after the start of cultures, if NGF was replaced by phorbol ester, or phorbol ester was replaced by NGF, the number of surviving sympathetic neurons was essentially the same in both groups, and the uptake of [3H]norepinephrine was also comparable when examined 2 days after the switchover. Interchangeability between phorbol ester and NGF in the survival of sympathetic neurons suggests that both agents act on the same subpopulation of neurons of the chick sympathetic ganglia. The protein kinase C activity of cytosol and particulate fractions of NGF-supported neurons was 0.14 and 0.09 pmol/min/mg protein, respectively. In phorbol estersupported neurons the activity in the paniculate fraction increased by about fivefold. Removal of the phorbol ester after 2 days resulted in restoration of the enzyme activity in <1 h, and readdition of the phorbol ester again increased the activity by fivefold. When NGF was added to these neurons (1 μg for 15 min), there was no change in the enzyme activity. Phorbol 13-acetate was ineffective in supporting sympathetic neurons in culture, as well as in enhancing protein kinase C activity. We also compared the protein kinase C activity of sympathetic neurons supported in culture by NGF and excess potassium (35 mM K+). Neurons supported in culture by 35 mM K+ for 2 days had almost eightfold more protein kinase C activity in their particulate fraction than in cytosol fraction. If NGF-supported neurons were acutely treated with excess K+, the protein kinase C activity was increased in the particulate fraction by about sevenfold in a concentration- and time-dependent manner. Excess K+ plus phorbol ester did not produce an additive effect on protein kinase C activity. PDB and excess K+ had no effect on cyclic AMP content of sympathetic neurons. In summary, the present data suggest that the neurotrophic action of PDB and excess K+ is probably mediated through protein kinase C.