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Phasic and Tonic Inhibition are Maintained Respectively by CaMKII and PKA in the Rat Visual Cortex.

Joo K, Yoon SH, Rhie DJ, Jang HJ - Korean J. Physiol. Pharmacol. (2014)

Bottom Line: However, maintenance of tonic inhibition relied on protein kinase A activity.Thus, phasic and tonic inhibition seem to be independently maintained and regulated by different signaling cascades in the same cell.These results suggest that neuromodulatory signals might differentially regulate phasic and tonic inhibition in response to changes in brain states.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, College of Medicine, The Catholic University of Korea, Seoul 137-701, Korea.

ABSTRACT
Phasic and tonic γ-aminobutyric acidA (GABAA) receptor-mediated inhibition critically regulate neuronal information processing. As these two inhibitory modalities have distinctive features in their receptor composition, subcellular localization of receptors, and the timing of receptor activation, it has been thought that they might exert distinct roles, if not completely separable, in the regulation of neuronal function. Inhibition should be maintained and regulated depending on changes in network activity, since maintenance of excitation-inhibition balance is essential for proper functioning of the nervous system. In the present study, we investigated how phasic and tonic inhibition are maintained and regulated by different signaling cascades. Inhibitory postsynaptic currents were measured as either electrically evoked events or spontaneous events to investigate regulation of phasic inhibition in layer 2/3 pyramidal neurons of the rat visual cortex. Tonic inhibition was assessed as changes in holding currents by the application of the GABAA receptor blocker bicuculline. Basal tone of phasic inhibition was maintained by intracellular Ca(2+) and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). However, maintenance of tonic inhibition relied on protein kinase A activity. Depolarization of membrane potential (5 min of 0 mV holding) potentiated phasic inhibition via Ca(2+) and CaMKII but tonic inhibition was not affected. Thus, phasic and tonic inhibition seem to be independently maintained and regulated by different signaling cascades in the same cell. These results suggest that neuromodulatory signals might differentially regulate phasic and tonic inhibition in response to changes in brain states.

No MeSH data available.


Related in: MedlinePlus

Regulation of tonic inhibition by PKA. (A) Cell-permeable myristoylated PKI (1 µM) was applied during the continuous recording of currents. Changes in holding currents and the amplitude of sIPSCs were investigated. Left upper panel shows a representative trace of current recording. Average amplitude of sIPSCs for 100 sec period before and after the application of drug was compared (indicated by braces and arrows in lower traces, showing averaged sIPSCs at the indicated period). Right panels plot individual data (symbols and thin symbols linked by lines) and averages (thick solid lines and thick symbols linked by lines). ***p<0.001 vs. baseline. (B) 8-Br-cAMP (10 µM) was applied during the continuous recording of currents. **p<0.01 vs. baseline.
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Figure 4: Regulation of tonic inhibition by PKA. (A) Cell-permeable myristoylated PKI (1 µM) was applied during the continuous recording of currents. Changes in holding currents and the amplitude of sIPSCs were investigated. Left upper panel shows a representative trace of current recording. Average amplitude of sIPSCs for 100 sec period before and after the application of drug was compared (indicated by braces and arrows in lower traces, showing averaged sIPSCs at the indicated period). Right panels plot individual data (symbols and thin symbols linked by lines) and averages (thick solid lines and thick symbols linked by lines). ***p<0.001 vs. baseline. (B) 8-Br-cAMP (10 µM) was applied during the continuous recording of currents. **p<0.01 vs. baseline.

Mentions: Since tonic GABAAR-mediated inhibition could also be regulated by phosphorylation [11], we investigated how kinases inhibitors affect tonic currents. Tonic currents were measured as the changes in holding currents by the application of the GABAAR blocker bicuculline (10 µM), recorded at a -75 mV holding potential. During the recording, AMPA, NMDA, and GABAB receptors were blocked by DNQX, D-AP5, and CGP 52432. Tonic currents under the control condition were 12.6±1.29 pA (n=12) (Fig. 3A). BAPTA or KN-93 in pipette solution had no effect on tonic currents (11.83±1.48 pA, n=11, 13.24±1.42 pA, n=11, p=0.698, p=0.743 vs. control, respectively) (Fig. 3B, C). However, PKI reduced the amplitude of tonic currents (7.43±1.27 pA, n=12, p<0.01 vs. control) (Fig. 3D). Since the PKA inhibitor reduced tonic currents, we tried to enhance PKA activity by including the PKA activator 8-Br-cAMP (10 µM) in the pipette solution. Tonic currents were slightly increased by 8-Br-cAMP to 16.2±1.68 pA (n=12, p=0.105 vs. control) (Fig. 3E). Chelerythrine or genistein did not affect the tonic currents (13.04±1.57 pA, n=11, 12.03±1.37 pA, n=11, p=0.831, p=0.764, vs. control, respectively) (Fig. 3F). Next, we investigated how the application of PKI and 8-Br-cAMP in the midst of recording affects the holding currents and the amplitude of sIPSCs (Fig. 4). Since PKI is impermeable to cell membrane, we used a cell-permeable myristoylated form of PKI in this experiment. Myristoylated PKI (1 µM) decreased holding currents by 6.59±0.83 (n=10, p<0.001) (Fig. 4A). On the contrary, 8-Br-cAMP (10 µM) increased currents by 4.11±0.93 (n=10, p<0.01) (Fig. 4B). The amplitudes of sIPSCs were not changed by both drugs (38.59±2.45 pA to 38.75±2.41 pA, 41.3±2.91 pA to 40.91±2.67 pA, for PKI and 8-Br-cAMP, p=0.82, p=0.469, respectively). Thus, in contrast to phasic inhibition, tonic GABAAR-mediated inhibition seemed to be maintained based on PKA activity in layer 2/3 pyramidal neurons of the visual cortex.


Phasic and Tonic Inhibition are Maintained Respectively by CaMKII and PKA in the Rat Visual Cortex.

Joo K, Yoon SH, Rhie DJ, Jang HJ - Korean J. Physiol. Pharmacol. (2014)

Regulation of tonic inhibition by PKA. (A) Cell-permeable myristoylated PKI (1 µM) was applied during the continuous recording of currents. Changes in holding currents and the amplitude of sIPSCs were investigated. Left upper panel shows a representative trace of current recording. Average amplitude of sIPSCs for 100 sec period before and after the application of drug was compared (indicated by braces and arrows in lower traces, showing averaged sIPSCs at the indicated period). Right panels plot individual data (symbols and thin symbols linked by lines) and averages (thick solid lines and thick symbols linked by lines). ***p<0.001 vs. baseline. (B) 8-Br-cAMP (10 µM) was applied during the continuous recording of currents. **p<0.01 vs. baseline.
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Related In: Results  -  Collection

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Show All Figures
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Figure 4: Regulation of tonic inhibition by PKA. (A) Cell-permeable myristoylated PKI (1 µM) was applied during the continuous recording of currents. Changes in holding currents and the amplitude of sIPSCs were investigated. Left upper panel shows a representative trace of current recording. Average amplitude of sIPSCs for 100 sec period before and after the application of drug was compared (indicated by braces and arrows in lower traces, showing averaged sIPSCs at the indicated period). Right panels plot individual data (symbols and thin symbols linked by lines) and averages (thick solid lines and thick symbols linked by lines). ***p<0.001 vs. baseline. (B) 8-Br-cAMP (10 µM) was applied during the continuous recording of currents. **p<0.01 vs. baseline.
Mentions: Since tonic GABAAR-mediated inhibition could also be regulated by phosphorylation [11], we investigated how kinases inhibitors affect tonic currents. Tonic currents were measured as the changes in holding currents by the application of the GABAAR blocker bicuculline (10 µM), recorded at a -75 mV holding potential. During the recording, AMPA, NMDA, and GABAB receptors were blocked by DNQX, D-AP5, and CGP 52432. Tonic currents under the control condition were 12.6±1.29 pA (n=12) (Fig. 3A). BAPTA or KN-93 in pipette solution had no effect on tonic currents (11.83±1.48 pA, n=11, 13.24±1.42 pA, n=11, p=0.698, p=0.743 vs. control, respectively) (Fig. 3B, C). However, PKI reduced the amplitude of tonic currents (7.43±1.27 pA, n=12, p<0.01 vs. control) (Fig. 3D). Since the PKA inhibitor reduced tonic currents, we tried to enhance PKA activity by including the PKA activator 8-Br-cAMP (10 µM) in the pipette solution. Tonic currents were slightly increased by 8-Br-cAMP to 16.2±1.68 pA (n=12, p=0.105 vs. control) (Fig. 3E). Chelerythrine or genistein did not affect the tonic currents (13.04±1.57 pA, n=11, 12.03±1.37 pA, n=11, p=0.831, p=0.764, vs. control, respectively) (Fig. 3F). Next, we investigated how the application of PKI and 8-Br-cAMP in the midst of recording affects the holding currents and the amplitude of sIPSCs (Fig. 4). Since PKI is impermeable to cell membrane, we used a cell-permeable myristoylated form of PKI in this experiment. Myristoylated PKI (1 µM) decreased holding currents by 6.59±0.83 (n=10, p<0.001) (Fig. 4A). On the contrary, 8-Br-cAMP (10 µM) increased currents by 4.11±0.93 (n=10, p<0.01) (Fig. 4B). The amplitudes of sIPSCs were not changed by both drugs (38.59±2.45 pA to 38.75±2.41 pA, 41.3±2.91 pA to 40.91±2.67 pA, for PKI and 8-Br-cAMP, p=0.82, p=0.469, respectively). Thus, in contrast to phasic inhibition, tonic GABAAR-mediated inhibition seemed to be maintained based on PKA activity in layer 2/3 pyramidal neurons of the visual cortex.

Bottom Line: However, maintenance of tonic inhibition relied on protein kinase A activity.Thus, phasic and tonic inhibition seem to be independently maintained and regulated by different signaling cascades in the same cell.These results suggest that neuromodulatory signals might differentially regulate phasic and tonic inhibition in response to changes in brain states.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, College of Medicine, The Catholic University of Korea, Seoul 137-701, Korea.

ABSTRACT
Phasic and tonic γ-aminobutyric acidA (GABAA) receptor-mediated inhibition critically regulate neuronal information processing. As these two inhibitory modalities have distinctive features in their receptor composition, subcellular localization of receptors, and the timing of receptor activation, it has been thought that they might exert distinct roles, if not completely separable, in the regulation of neuronal function. Inhibition should be maintained and regulated depending on changes in network activity, since maintenance of excitation-inhibition balance is essential for proper functioning of the nervous system. In the present study, we investigated how phasic and tonic inhibition are maintained and regulated by different signaling cascades. Inhibitory postsynaptic currents were measured as either electrically evoked events or spontaneous events to investigate regulation of phasic inhibition in layer 2/3 pyramidal neurons of the rat visual cortex. Tonic inhibition was assessed as changes in holding currents by the application of the GABAA receptor blocker bicuculline. Basal tone of phasic inhibition was maintained by intracellular Ca(2+) and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). However, maintenance of tonic inhibition relied on protein kinase A activity. Depolarization of membrane potential (5 min of 0 mV holding) potentiated phasic inhibition via Ca(2+) and CaMKII but tonic inhibition was not affected. Thus, phasic and tonic inhibition seem to be independently maintained and regulated by different signaling cascades in the same cell. These results suggest that neuromodulatory signals might differentially regulate phasic and tonic inhibition in response to changes in brain states.

No MeSH data available.


Related in: MedlinePlus