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Copyright of Brazilian Journal of Biology is the property of Instituto Internacional de Ecologia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Arginine vasopressin (AVP) induces an increase in intracellular Ca 2+ concentration ([Ca 2+ ] i ) with an oscillatory pattern in isolated perfused kidney inner medullary collecting duct (IMCD). The AVP-induced Ca 2+ mobilization in inner medullary collecting ducts is essential for apical exocytosis and is mediated by the exchange protein directly activated by cyclic adenosine monophosphate (Epac). Murine principal kidney cortical collecting duct cells (mpkCCD) is the cell model used for transcriptomic and phosphoproteomic studies of AVP signaling in kidney collecting duct. The present study examined the characteristics of Ca 2+ mobilization in mpkCCD cells, and utilized mpkCCD as a model to investigate the Epac-induced intracellular and intra-organellar Ca 2+ mobilization. Ca 2+ mobilization in cytosol, endoplasmic reticulum lumen, and mitochondrial matrix were monitored with a Ca 2+ sensitive fluorescent probe and site-specific Ca 2+ sensitive biosensors. Fluorescence images of mpkCCD cells and isolated perfused inner medullary duct were collected with confocal microscopy. Cell permeant ligands of ryanodine receptors (RyRs) and inositol 1,4,5 trisphosphate receptors (IP 3 Rs) both triggered increase of [Ca 2+ ] i and Ca 2+ oscillations in mpkCCD cells as reported previously in IMCD. The cell permeant Epac-specific cAMP analog Me-cAMP/AM also caused a robust Ca 2+ mobilization and oscillations in mpkCCD cells. Using biosensors to monitor endoplasmic reticulum (ER) luminal Ca 2+ and mitochondrial matrix Ca 2+ , Me-cAMP/AM not only triggered Ca 2+ release from ER into cytoplasm, but also shuttled Ca 2+ from ER into mitochondria. The Epac-agonist induced synchronized Ca 2+ spikes in cytosol and mitochondrial matrix, with concomitant declines in ER luminal Ca 2+ . Me-cAMP/AM also effectively triggered store-operated Ca 2+ entry (SOCE), suggesting that Epac-agonist is capable of depleting ER Ca 2+ stores. These Epac-induced intracellular and inter-organelle Ca 2+ signals were mimicked by the RyR agonist 4-CMC, but they were distinctly different from IP 3 R activation. The present study hence demonstrated that mpkCCD cells retain all reported features of Ca 2+ mobilization observed in isolated perfused IMCD. It further revealed information on the dynamics of Epac-induced RyR-dependent Ca 2+ signaling and ER-mitochondrial Ca 2+ transfer. ER-mitochondrial Ca 2+ coupling may play a key role in the regulation of ATP and reactive oxygen species (ROS) production in the mitochondria along the nephron. Our data suggest that mpkCCD cells can serve as a renal cell model to address novel questions of how mitochondrial Ca 2+ regulates cytosolic Ca 2+ signals, inter-organellar Ca 2+ signaling, and renal tubular functions., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Yip, Ribeiro-Silva, Cha, Rieg and Sham.)

Junctions between the endoplasmic reticulum (ER) and the plasma membrane (PM) are specialized membrane contacts ubiquitous in eukaryotic cells. Concentration of intracellular signaling machinery near ER-PM junctions allows these domains to serve critical roles in lipid and Ca 2+ signaling and homeostasis. Subcellular compartmentalization of protein kinase A (PKA) signaling also regulates essential cellular functions, however, no specific association between PKA and ER-PM junctional domains is known. Here, we show that in brain neurons type I PKA is directed to Kv2.1 channel-dependent ER-PM junctional domains via SPHKAP, a type I PKA-specific anchoring protein. SPHKAP association with type I PKA regulatory subunit RI and ER-resident VAP proteins results in the concentration of type I PKA between stacked ER cisternae associated with ER-PM junctions. This ER-associated PKA signalosome enables reciprocal regulation between PKA and Ca 2+ signaling machinery to support Ca 2+ influx and excitation-transcription coupling. These data reveal that neuronal ER-PM junctions support a receptor-independent form of PKA signaling driven by membrane depolarization and intracellular Ca 2+ , allowing conversion of information encoded in electrical signals into biochemical changes universally recognized throughout the cell., (© 2023. Springer Nature Limited.)

Calcium (Ca 2+ ) is an essential component in intracellular signaling of brain cells, and its control mechanisms are of great interest in biological systems. Ca 2+ can signal differently in neurons and glial cells using the same intracellular pathways or cell membrane structural components. These types of machinery are responsible for entry, permanence, and removal of Ca 2+ from the cellular environment and are of vital importance for brain homeostasis. This review highlights the importance of Ca 2+ in neuronal and glial cell physiology as well as aspects of learning, memory, and Alzheimer's disease, focusing on the involvement of L-type voltage-gated Ca 2+ channels., (Copyright © 2019 IBRO. Published by Elsevier Ltd. All rights reserved.)

Myogenic contraction of renal arterioles is an important regulatory mechanism for renal blood flow autoregulation. We have previously demonstrated that integrin-mediated mechanical force increases the occurrence of Ca 2+ sparks in freshly isolated renal vascular smooth muscle cells (VSMCs). To further test whether the generation of Ca 2+ sparks is a downstream signal of mechanotransduction in pressure-induced myogenic constriction, the relationship between Ca 2+ sparks and transmural perfusion pressure was investigated in intact VSMCs of pressurized rat afferent arterioles. Spontaneous Ca 2+ sparks were found in VSMCs when afferent arterioles were perfused at 80 mmHg. The spark frequency was significantly increased when perfusion pressure was increased to 120 mmHg. A similar increase of spark frequency was also observed in arterioles stimulated with β 1 -integrin-activating antibody. Moreover, spark frequency was significantly higher in arterioles of spontaneous hypertensive rats at 80 and 120 mmHg. Spontaneous membrane current recorded using whole cell perforated patch in renal VSMCs showed predominant activity of spontaneous transient inward currents instead of spontaneous transient outward currents when holding potential was set close to physiological resting membrane potential. Real-time PCR and immunohistochemistry confirmed the expression of Ca 2+ -activated Cl - channel (Cl Ca ) TMEM16A in renal VSMCs. Inhibition of TMEM16A with T16Ainh-A01 impaired the pressure-induced myogenic contraction in perfused afferent arterioles. Our study, for the first time to our knowledge, detected Ca 2+ sparks in VSMCs of intact afferent arterioles, and their frequencies were positively modulated by the perfusion pressure. Our results suggest that Ca 2+ sparks may couple to Cl Ca channels and trigger pressure-induced myogenic constriction via membrane depolarization.

Solid tumors tend to have a more glycolytic metabolism leading to an accumulation of acidic metabolites in their cytosol, and consequently, their intracellular pH (pHi) turns critically lower if the cells do not handle the acid excess. Recently, it was proposed that the voltage gated proton channels (HV1) can regulate the pHi in several cancers. Here we report the functional expression of voltage gated proton channels in a human glioblastoma multiforme (GBM) cell line, the most common and lethal brain tumor. T98G cells presented an outward, slow activating voltage-dependent proton current, which was also ΔpH-dependent and inhibited by ZnCl2, characterizing it as being conducted by HV1 channels. Furthermore, blocking HV1 channels with ZnCl2 significantly reduced the pHi, cell survival, and migration, indicating an important role for HV1 for tumor proliferation and progression in GBM. Overall, our results suggest that HV1 channels can be a new therapeutic target for GBM.