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Expanding the neuron's calcium signaling repertoire: intracellular calcium release via voltage-induced PLC and IP3R activation.

Ryglewski S, Pflueger HJ, Duch C - PLoS Biol. (2007)

Bottom Line: Specific and independent regulation of these vital cellular processes is achieved by a rich bouquet of different calcium signaling mechanisms within the neuron, which either can operate independently or may act in concert.This study demonstrates the existence of a novel calcium signaling mechanism by simultaneous patch clamping and calcium imaging from acutely isolated central neurons.This allows neurons to monitor activity by intracellular calcium release without relying on calcium as the input signal and opens up new insights into intracellular signaling, developmental regulation, and information processing in neuronal compartments lacking calcium channels.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biology/Neurobiology, Free University of Berlin, Berlin, Germany.

ABSTRACT
Neuronal calcium acts as a charge carrier during information processing and as a ubiquitous intracellular messenger. Calcium signals are fundamental to numerous aspects of neuronal development and plasticity. Specific and independent regulation of these vital cellular processes is achieved by a rich bouquet of different calcium signaling mechanisms within the neuron, which either can operate independently or may act in concert. This study demonstrates the existence of a novel calcium signaling mechanism by simultaneous patch clamping and calcium imaging from acutely isolated central neurons. These neurons possess a membrane voltage sensor that, independent of calcium influx, causes G-protein activation, which subsequently leads to calcium release from intracellular stores via phospholipase C and inositol 1,4,5-trisphosphate receptor activation. This allows neurons to monitor activity by intracellular calcium release without relying on calcium as the input signal and opens up new insights into intracellular signaling, developmental regulation, and information processing in neuronal compartments lacking calcium channels.

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Voltage-Induced Intracellular Calcium Signals That Occur in the Absence of Extracellular Calcium Do Not Depend on RYRs(A) In dantrolene-loaded, acutely isolated DUM neurons in TEA- and TTX-containing saline, a voltage step from −90 mV holding to 0 mV test potential causes a calcium inward and a calcium-activated potassium outward current accompanied by an intracellular calcium signal.(B) After 3 min in calcium-free saline, a slow elevation in intracellular calcium occurs in response to the same voltage step as in (A), although RYRs are blocked by intracellular application of dantrolene (100 nM).(C) Switching back to calcium-containing extracellular saline restores membrane currents and intracellular calcium signals as observed in (A).
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pbio-0050066-g003: Voltage-Induced Intracellular Calcium Signals That Occur in the Absence of Extracellular Calcium Do Not Depend on RYRs(A) In dantrolene-loaded, acutely isolated DUM neurons in TEA- and TTX-containing saline, a voltage step from −90 mV holding to 0 mV test potential causes a calcium inward and a calcium-activated potassium outward current accompanied by an intracellular calcium signal.(B) After 3 min in calcium-free saline, a slow elevation in intracellular calcium occurs in response to the same voltage step as in (A), although RYRs are blocked by intracellular application of dantrolene (100 nM).(C) Switching back to calcium-containing extracellular saline restores membrane currents and intracellular calcium signals as observed in (A).

Mentions: In principle, in neurons, calcium release from the ER is mediated either by IP3R or by RYR activation [10]. In insect DUM neurons, RYRs can be reliably blocked by intracellular application of 100 nM dantrolene [19]. To further prove the effectiveness of intracellular dantrolene in our experiments, we activated RYRs by bath application of caffeine, imaged the resulting calcium signal caused be RYR activation, and then demonstrated that dantrolene completely blocked calcium release in responses to caffeine (see Figure S1). However, dantrolene had no effect on voltage-induced increases in [Ca2+]i under calcium-free conditions (Figure 3), demonstrating that this effect was not mediated by RYRs. Under calcium-free extracellular conditions, calcium inward current was zero, but an increase in intracellular calcium indicator fluorescence of 32 ± 6% amplitude still occurred in response to the depolarizing current step (Figure 3B).


Expanding the neuron's calcium signaling repertoire: intracellular calcium release via voltage-induced PLC and IP3R activation.

Ryglewski S, Pflueger HJ, Duch C - PLoS Biol. (2007)

Voltage-Induced Intracellular Calcium Signals That Occur in the Absence of Extracellular Calcium Do Not Depend on RYRs(A) In dantrolene-loaded, acutely isolated DUM neurons in TEA- and TTX-containing saline, a voltage step from −90 mV holding to 0 mV test potential causes a calcium inward and a calcium-activated potassium outward current accompanied by an intracellular calcium signal.(B) After 3 min in calcium-free saline, a slow elevation in intracellular calcium occurs in response to the same voltage step as in (A), although RYRs are blocked by intracellular application of dantrolene (100 nM).(C) Switching back to calcium-containing extracellular saline restores membrane currents and intracellular calcium signals as observed in (A).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1808487&req=5

pbio-0050066-g003: Voltage-Induced Intracellular Calcium Signals That Occur in the Absence of Extracellular Calcium Do Not Depend on RYRs(A) In dantrolene-loaded, acutely isolated DUM neurons in TEA- and TTX-containing saline, a voltage step from −90 mV holding to 0 mV test potential causes a calcium inward and a calcium-activated potassium outward current accompanied by an intracellular calcium signal.(B) After 3 min in calcium-free saline, a slow elevation in intracellular calcium occurs in response to the same voltage step as in (A), although RYRs are blocked by intracellular application of dantrolene (100 nM).(C) Switching back to calcium-containing extracellular saline restores membrane currents and intracellular calcium signals as observed in (A).
Mentions: In principle, in neurons, calcium release from the ER is mediated either by IP3R or by RYR activation [10]. In insect DUM neurons, RYRs can be reliably blocked by intracellular application of 100 nM dantrolene [19]. To further prove the effectiveness of intracellular dantrolene in our experiments, we activated RYRs by bath application of caffeine, imaged the resulting calcium signal caused be RYR activation, and then demonstrated that dantrolene completely blocked calcium release in responses to caffeine (see Figure S1). However, dantrolene had no effect on voltage-induced increases in [Ca2+]i under calcium-free conditions (Figure 3), demonstrating that this effect was not mediated by RYRs. Under calcium-free extracellular conditions, calcium inward current was zero, but an increase in intracellular calcium indicator fluorescence of 32 ± 6% amplitude still occurred in response to the depolarizing current step (Figure 3B).

Bottom Line: Specific and independent regulation of these vital cellular processes is achieved by a rich bouquet of different calcium signaling mechanisms within the neuron, which either can operate independently or may act in concert.This study demonstrates the existence of a novel calcium signaling mechanism by simultaneous patch clamping and calcium imaging from acutely isolated central neurons.This allows neurons to monitor activity by intracellular calcium release without relying on calcium as the input signal and opens up new insights into intracellular signaling, developmental regulation, and information processing in neuronal compartments lacking calcium channels.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biology/Neurobiology, Free University of Berlin, Berlin, Germany.

ABSTRACT
Neuronal calcium acts as a charge carrier during information processing and as a ubiquitous intracellular messenger. Calcium signals are fundamental to numerous aspects of neuronal development and plasticity. Specific and independent regulation of these vital cellular processes is achieved by a rich bouquet of different calcium signaling mechanisms within the neuron, which either can operate independently or may act in concert. This study demonstrates the existence of a novel calcium signaling mechanism by simultaneous patch clamping and calcium imaging from acutely isolated central neurons. These neurons possess a membrane voltage sensor that, independent of calcium influx, causes G-protein activation, which subsequently leads to calcium release from intracellular stores via phospholipase C and inositol 1,4,5-trisphosphate receptor activation. This allows neurons to monitor activity by intracellular calcium release without relying on calcium as the input signal and opens up new insights into intracellular signaling, developmental regulation, and information processing in neuronal compartments lacking calcium channels.

Show MeSH
Related in: MedlinePlus