Organelle calcium-derived voltage oscillations in pacemaker neurons drive the motor program for food-seeking behavior in Aplysia

The expression of motivated behaviors depends on both external and internally-arising neural stimuli, yet the intrinsic releasing mechanisms for such variably occurring behaviors remain elusive. In isolated nervous system preparations of Aplysia, we have found that irregularly expressed cycles of motor output underlying food-seeking behavior arise from regular membrane potential oscillations of varying magnitude in an identified pair of interneurons (B63) in the bilateral buccal ganglia. This rhythmic signal, which is specific to the B63 cells, is generated by organelle-derived intracellular calcium fluxes that activate voltage-independent plasma membrane channels. The resulting voltage oscillation spreads throughout a subset of gap junction-coupled buccal network neurons and by triggering plateau potential-mediated bursts in B63, can initiate motor output driving food-seeking action. Thus, an atypical neuronal pacemaker mechanism, based on rhythmic intracellular calcium store release and intercellular propagation, can act as an autonomous intrinsic releaser for the occurrence of a motivated behavior.

Organelle calcium-derived voltage oscillations in pacemaker neurons drive food-seeking behavior in Aplysia

The expression of motivated behaviors depends on both external and internally-arising neural stimuli, yet the intrinsic releasing mechanisms for such variably occurring behaviors remain elusive. In isolated nervous system preparations of Aplysia, we have found that irregularly expressed cycles of motor output underlying food-seeking behavior arise from regular membrane potential oscillations of varying magnitude in an identified pair of interneurons (B63) in the bilateral buccal ganglia. This rhythmic signal, which is endogenous and specific to the B63 cells, is generated by organelle-derived intracellular calcium fluxes that activate voltage-independent plasma membrane channels. The resulting voltage oscillation spreads throughout a subset of gap junction-coupled buccal network neurons and by triggering plateau potential-mediated bursts in B63, can initiate motor output driving food-seeking action. Thus, an atypical neuronal pacemaker mechanism, based on rhythmic intracellular calcium store release and intercellular propagation, can act as an autonomous intrinsic releaser for the occurrence of a motivated behavior.

Comparison of Vascular Responses to Vasoconstrictors in Human Placenta in Preeclampsia between Preterm and Later Term

Background: Placental blood vessels play important roles in maternal-fetal circulation. Although pathologic mechanisms of preeclampsia are unclear, it is known that placental vascular dysfunction could contribute to pregnant hypertension. However, placental micro-vessel function or dysfunction at preterm has not been investigated. Methods: Human placentas from normal and preeclamptic pregnancies at preterm and term were obtained. Placental micro-vessels were used for determining vascular tension and responses to various vasoconstrictors as well as intracellular calcium store capability. It was the first time to show vascular responses in placental arteries to angiotensin II, endothelin-1, and other vascular drugs at preterm. Results: Compared to the control, placental vascular contractile responses to angiotensin II and caffeine were significantly decreased, while placental vascular responses to KCl, endothelin-1, and bradykinin were not significantly altered in the later term group in preeclampsia. In comparison of placental micro-vessel tension between the preterm and later term, caffeine- and serotonin-induced vascular contractions were significantly weaker in the preterm than that in the later term. On the contrary, vascular response to angiotensin II was increased in the preterm preeclampsia, while KCl-, endothelin-1, and bradykinin-mediated placental vessel responses in the preterm preeclampsia were similar to that in later term preeclampsia. Conclusion: New data showed that micro-vessel responses to angiotensin II and serotonin, not endothelin- 1 or bradykinin, were significantly reduced in the human placentas at preterm, and intracellular Ca2+ store capacity was damaged too, providing important information on possible contributions of placental vascular dysfunction to pregnant hypertension.

Voltage-Dependent Calcium Channels, Calcium Binding Proteins, and Their Interaction in the Pathological Process of Epilepsy

As an important second messenger, the calcium ion (Ca2+) plays a vital role in normal brain function and in the pathophysiological process of different neurodegenerative diseases including Alzheimer’s disease (AD), Parkinson’s disease (PD), and epilepsy. Ca2+ takes part in the regulation of neuronal excitability, and the imbalance of intracellular Ca2+ is a trigger factor for the occurrence of epilepsy. Several anti-epileptic drugs target voltage-dependent calcium channels (VDCCs). Intracellular Ca2+ levels are mainly controlled by VDCCs located in the plasma membrane, the calcium-binding proteins (CBPs) inside the cytoplasm, calcium channels located on the intracellular calcium store (particular the endoplasmic reticulum/sarcoplasmic reticulum), and the Ca2+-pumps located in the plasma membrane and intracellular calcium store. So far, while many studies have established the relationship between calcium control factors and epilepsy, the mechanism of various Ca2+ regulatory factors in epileptogenesis is still unknown. In this paper, we reviewed the function, distribution, and alteration of VDCCs and CBPs in the central nervous system in the pathological process of epilepsy. The interaction of VDCCs with CBPs in the pathological process of epilepsy was also summarized. We hope this review can provide some clues for better understanding the mechanism of epileptogenesis, and for the development of new anti-epileptic drugs targeting on VDCCs and CBPs.

Lysosomal Potassium Channels: Potential Roles in Lysosomal Function and Neurodegenerative Diseases

Background & Objective: The lysosome is a membrane-enclosed organelle widely found in every eukaryotic cell. It has been deemed as the stomach of the cells. Recent studies revealed that it also functions as an intracellular calcium store and is a platform for nutrient-dependent signal transduction. Similar with the plasma membrane, the lysosome membrane is furnished with various proteins, including pumps, ion channels and transporters. So far, two types of lysosomal potassium channels have been identified: large-conductance and Ca2+-activated potassium channel (BK) and TMEM175. TMEM175 has been linked to several neurodegeneration diseases, such as the Alzheimer and Parkinson disease. Recent studies showed that TMEM175 is a lysosomal potassium channel with novel architecture and plays important roles in setting the lysosomal membrane potential and maintaining pH stability. TMEM175 deficiency leads to compromised lysosomal function, which might be responsible for the pathogenesis of related diseases. BK is a well-known potassium channel for its function on the plasma membrane. Studies from two independent groups revealed that functional BK channels are also expressed on the lysosomal plasma membrane. Dysfunction of BK causes impaired lysosomal calcium signaling and abnormal lipid accumulation, a featured phenotype of most lysosomal storage diseases (LSDs). Boosting BK activity could rescue the lipid accumulation in several LSD cell models. Overall, the lysosomal potassium channels are essential for the lysosome physiological function, including lysosomal calcium signaling and autophagy. The dysfunction of lysosomal potassium channels is related to some neurodegeneration disorders. Conclusion: Therefore, lysosomal potassium channels are suggested as potential targets for the intervention of lysosomal disorders.

Observation of the molecular organization of calcium release sites in fast- and slow-twitch skeletal muscle with nanoscale imaging

Localization microscopy is a fairly recently introduced super-resolution fluorescence imaging modality capable of achieving nanometre-scale resolution. We have applied the dSTORM variation of this method to image intracellular molecular assemblies in skeletal muscle fibres which are large cells that critically rely on nanoscale signalling domains, the triads. Immunofluorescence staining in fixed adult rat skeletal muscle sections revealed clear differences between fast- and slow-twitch fibres in the molecular organization of ryanodine receptors (RyRs; the primary calcium release channels) within triads. With the improved resolution offered by dSTORM, abutting arrays of RyRs in transverse view of fast fibres were observed in contrast to the fragmented distribution on slow-twitch muscle that were approximately 1.8 times shorter and consisted of approximately 1.6 times fewer receptors. To the best of our knowledge, for the first time, we have quantified the nanometre-scale spatial association between triadic proteins using multi-colour super-resolution, an analysis difficult to conduct with electron microscopy. Our findings confirm that junctophilin-1 (JPH1), which tethers the sarcoplasmic reticulum ((SR) intracellular calcium store) to the tubular (t-) system at triads, was present throughout the RyR array, whereas JPH2 was contained within much smaller nanodomains. Similar imaging of the primary SR calcium buffer, calsequestrin (CSQ), detected less overlap of the triad with CSQ in slow-twitch muscle supporting greater spatial heterogeneity in the luminal Ca 2+ buffering when compared with fast twitch muscle. Taken together, these nanoscale differences can explain the fundamentally different physiologies of fast- and slow-twitch muscle.

Abstract P225: Possible Involvement of Homer-1b/c in Gq-Mediated Hypertrophy in Cardiomyocytes

Receptor activation of Gq causes hypertrophy in cardiomyocytes, via the activation of phospholipase Cβ 1b (PLCβ1b). PLCβ1b, localizes to the cardiac sarcolemma through an interaction with the multi-domain scaffolding molecule Shank-3 (SH3 and multiple ankyrin repeat domains protein 3; Grubb et al., 2011), which is required for PLC activation and for hypertrophic responses. In the CNS, Shank-3 forms higher order oligomeric complexes with three isoforms of Homer protein homolog 1 (Homer-1), Homer-1a, Homer-1b and Homer-1c. Homer-1b and Homer-1c link G-protein coupled receptors, ionotropic receptors, canonical transient receptor potential channel (TrpC) and intracellular calcium store regulators into a signaling complex. Homer-1a acts as a natural dominant negative, in dynamic competition with Homer-1b and Homer-1c. Neonatal rat ventricular myocytes (NRVM) infected with adenovirus expressing either Gαq(Q209L) (constitutively active Gαq), or its immediate down-stream effector, PLCβ1b, increased Homer-1b/c transcription. Incubation with phenylephrine/propranalol (α 1 -adrenergic agonist, PE/Pro) also increased Homer-1b/c, but not Homer-1a, mRNA. All treatments caused cardiomyocyte hypertrophy. There was no comparable increase in Homer-1b/c mRNA in NRVM expressing PLCβ1a (inactive splice variant) or incubated with fetal calf serum to induce hypertrophy by Gq-independent mechanisms. Homer-1b/c protein induced by PLCβ1b, Gαq or PE/Pro was primarily localized close to the sarcolemma along with Shank3, PLCβ1b and TrpC4. We conclude that Gαq/PLCβ1b-mediated signaling leads to the up-regulation of Homer-1b/c, that co-localizes with a signaling complex close to the sacrolemma. Induction of Homer-1b/c may be critical in facilitating localized Ca 2+ signaling and thereby promoting Gq dependent hypertrophy.