Autonomously active protein kinase C in the maintenance phase of N-methyl-D-aspartate receptor-independent long term potentiation - PubMed (original) (raw)

Comparative Study

. 1994 Nov 11;269(45):27958-63.

Affiliations

Comparative Study

Autonomously active protein kinase C in the maintenance phase of N-methyl-D-aspartate receptor-independent long term potentiation

C M Powell et al. J Biol Chem. 1994.

Abstract

In area CA1 of the hippocampus, the induction of long term potentiation (LTP) requires activation of either N-methyl-D-aspartate receptors (NMDA receptor-dependent LTP) or voltage-gated Ca2+ channels (NMDA receptor-independent LTP). We have investigated biochemical sequelae of NMDA receptor-independent LTP induction. We find that a persistent increase in second messenger-independent protein kinase C activity is associated with the maintenance phase of NMDA receptor-independent LTP. This increase in protein kinase C activity is prevented by blocking LTP with nifedipine, a Ca2+ channel antagonist, or kynurenic acid, a nonselective glutamate receptor antagonist. Additionally, we find an increase in the catalytic fragment of protein kinase C (PKM) in the maintenance phase of NMDA receptor-independent LTP, indicating that proteolytic activation of protein kinase C may account for its autonomous activation. This increase in the catalytic fragment of protein kinase C is also prevented by blocking LTP induction. These results are the first to demonstrate that persistent protein kinase C activation is a possible mechanism for the maintenance of NMDA receptor-independent LTP.

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Figures

Fig. 1

Fig. 1. Basal PKC activity is increased 45 min into the maintenance phase of LTP_K_

A, time course of LTP_K_. pEPSP slope is plotted as a function of time. Each point represents the slope of the average of four consecutive traces normalized to the base-line average of each experiment in this and all subsequent pEPSP time course figures. TEA (25 m

m

) application in the presence of 50 µ

m dl

-2-amino-5-phosphonovaleric acid (APV) caused a lasting potentiation (172 ± 12%, n = 14). B, example pEPSPs taken before (a), during (b), and 45 min after (c) TEA washout. C, increase in basal, Ca2+-independent PKC activity 45 min into LTP_K_ (solid bars). Addition of PKC-(19–36) (5 µ

m

) to kinase assays in vitro blocks the increase in PKC activity associated with LIT_K_ (hatched bars).

Fig. 2

Fig. 2. Blocking LTP_K_ with kynurenic acid prevents the increase in PKC activity

A, LTP_K_ was completely blocked when TEA was applied in the presence of 10 m

m

kynurenic acid (n = 5). B, physiological effects of kynurenic acid (10 m

m

) are completely reversible (n = 4). C, no significant increase in PKC activity was observed in slices exposed to TEA in the presence of kynurenic acid. Control slices were similarly perfused with 10 m

m

kynurenic acid.

Fig. 3

Fig. 3. Blocking LTP_K_ with 10 µm nifedipine prevents the increase in basal PKC activity

A, time course of pEPSP slope before and after TEA application (25 m

m

) in the presence of 10 µ

m

nifedipine and 50 µ

m

APV. Potentiation is significantly reduced to 108 ± 1% of base line 45 min after TEA washout (n = 5). B, no change in basal PKC activity occurs after TEA application in the presence of 10 µ

m

nifedipine and 50 µ

m

APV (n = 5). Control slices were similarly perfused with nifedipine.

Fig. 4

Fig. 4. Time course of the increase in basal PKC activity associated with LTP_K_ maintenance

A, 3-h time course of LTP_K_. pEPSP slope is plotted as a function of time. TEA (25 m

m

) application In the presence of 50 µ

m

APV caused a lasting potentiation (144 ± 6%, n = 7). Inset numbers represent times in minutes where PKC activity was measured in B. B, the increase in PKC activity associated with LTP_K_ persists for at least 3 h following TEA application. Basal PKC activity was measured in separate experiments at various time intervals following onset of TEA washout (5 min, n = 5; 20 min, n = 7; 45 min, n = 14; 180 min, n = 7). A significant increase in basal PKC activity was observed 45 and 180 min following TEA washout (* indicates statistical significance using an unpaired Student's t test, p < 0.05). No significant change in total Ca2+/phosphatidylserine/oleoylacetylglycerol-stimulated PKC activity was observed at any time point (not shown).

Fig. 5

Fig. 5. Proteolytic activation of PKC is associated with the increase in PKC activity

A, a significant increase in the proteolytically activated fragment of PKC occurs 45 min into LTP_K_ maintenance. Left, example Western blot analysis reveals a statistically significant increase in the 45-kDa immunoreactive protein (PKC Fragment) 45 min into LTP_K_ maintenance. Right, grouped densitometry data from LTP_K_ Western blot experiments reveal a statistically significant increase in PKM immunoreactivity (119 ± 6% of control, n = 10, p = 0.009). B, no significant change in native PKC immunoreactivity occurs during LTP_K_. Left, example Western blot analysis (shorter exposure than in A) using a polyclonal antibody raised against classical PKC isoforms demonstrates no change in native PKC immunoreactivity (PKC). Right, grouped densitometry data from LTP_K_ Western blot experiments reveal no significant change in the immunoreactivity of native PKC (n = 10, 45-min time point).

Fig. 6

Fig. 6. Blocking LTP_K_ with kynurenic (kyn.) acid prevents the increase in PKM associated with LTP_K_ maintenance

Left, example Western blot analysis using a polyclonal antibody raised against classical PKC isoforms demonstrates no significant increase in PKM when LTP_K_ is blocked by kynurenic acid. Right, grouped densitometry data from kynurenic acid block experiments show no increase in PKM when LTP_K_ is blocked by kynurenic acid (89 ± 8% of control, n = 6).

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