A nicardipine-sensitive Ca2+ entry contributes to the hypotonicity-induced increase in [Ca2+]i of principal cells in rat cortical collecting duct

Hydrogen sulfide induces Ca2+ influx in the principal cells of rat cortical collecting ducts

Hydrogen sulfide (H2S) acts as a gas-signaling agent in various tissues. Although it has been reported that endogenous enzymes that generate H2S are expressed abundantly in the kidney, few reports examine cellular responses to H2S in renal tubular epithelial cells. In this study, we investigated the effects of NaHS, an H2S donor, and l-cysteine, a substrate for H2S production, on the principal cells of rat cortical collecting ducts (CCDs). NaHS increased the intracellular Ca2+ concentration ([Ca2+]i) in the principal cells. The removal of extracellular Ca2+ largely attenuated the [Ca2+]i response. The TRPV4 channel blocker significantly inhibited the effect of NaHS. Extracellular administration of l-cysteine also elicited a rise in [Ca2+]i. Prior treatment of CCDs with AOAA, an inhibitor of H2S production enzyme, l-cysteine-induced [Ca2+]i response was significantly reduced. These results suggest that not only exogenous H2S but also endogenously produced H2S triggers the extracellular influx pathway of Ca2+ in the principal cells of rat CCDs.

Identification of a selective manganese ionophore that enables nonlethal quantification of cellular manganese

Available assays for measuring cellular manganese (Mn) levels require cell lysis, restricting longitudinal experiments and multiplexed outcome measures. Conducting a screen of small molecules known to alter cellular Mn levels, we report here that one of these chemicals induces rapid Mn efflux. We describe this activity and the development and implementation of an assay centered on this small molecule, named manganese-extracting small molecule (MESM). Using inductively-coupled plasma-MS, we validated that this assay, termed here "manganese-extracting small molecule estimation route" (MESMER), can accurately assess Mn in mammalian cells. Furthermore, we found evidence that MESM acts as a Mn-selective ionophore, and we observed that it has increased rates of Mn membrane transport, reduced cytotoxicity, and increased selectivity for Mn over calcium compared with two established Mn ionophores, calcimycin (A23187) and ionomycin. Finally, we applied MESMER to test whether prior Mn exposures subsequently affect cellular Mn levels. We found that cells receiving continuous, elevated extracellular Mn accumulate less Mn than cells receiving equally-elevated Mn for the first time for 24 h, indicating a compensatory cellular homeostatic response. Use of the MESMER assay versus a comparable detergent lysis-based assay, cellular Fura-2 Mn extraction assay, reduced the number of cells and materials required for performing a similar but cell lethality-based experiment to 25% of the normally required sample size. We conclude that MESMER can accurately quantify cellular Mn levels in two independent cells lines through an ionophore-based mechanism, maintaining cell viability and enabling longitudinal assessment within the same cultures.

Anti-neuroinflammatory effects of the calcium channel blocker nicardipine on microglial cells: implications for neuroprotection

BACKGROUND/OBJECTIVE

Nicardipine is a calcium channel blocker that has been widely used to control blood pressure in severe hypertension following events such as ischemic stroke, traumatic brain injury, and intracerebral hemorrhage. However, accumulating evidence suggests that inflammatory processes in the central nervous system that are mediated by microglial activation play important roles in neurodegeneration, and the effect of nicardipine on microglial activation remains unresolved.

METHODOLOGY/PRINCIPAL FINDINGS

In the present study, using murine BV-2 microglia, we demonstrated that nicardipine significantly inhibits microglia-related neuroinflammatory responses. Treatment with nicardipine inhibited microglial cell migration. Nicardipine also significantly inhibited LPS plus IFN-γ-induced release of nitric oxide (NO), and the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Furthermore, nicardipine also inhibited microglial activation by peptidoglycan, the major component of the Gram-positive bacterium cell wall. Notably, nicardipine also showed significant anti-neuroinflammatory effects on microglial activation in mice in vivo.

CONCLUSION/SIGNIFICANCE

The present study is the first to report a novel inhibitory role of nicardipine on neuroinflammation and provides a new candidate agent for the development of therapies for inflammation-related neurodegenerative diseases.

Interaction between Calcineurin and Ca/Calmodulin Kinase-II in Modulating Cellular Functions

Roles of calcineurin (CaN), a Ca²⁺/calmodulin- (CaM-) dependent protein phosphatase, and Ca²⁺/CaM-dependent protein kinase-II (CaMKII) in modulating K⁺ channel activity and the intracellular Ca²⁺ concentration ([Ca²⁺]_i) have been investigated in renal tubule epithelial cells. The channel current through the cell membrane was recorded with the patch-clamp technique, and [Ca²⁺]_i was monitored using fura-2 imaging. We found that a CaN-inhibitor, cyclosporin A (CyA), lowered the K⁺ channel activity and elevated [Ca²⁺]_i, suggesting that CyA closes K⁺ channels and opens Ca²⁺-release channels of the cytosolic Ca²⁺-store. Moreover, both of these responses were blocked by KN-62, an inhibitor of CaMKII. It is suggested that the CyA-mediated response results from the activation of CaMKII. Indeed, Western blot analysis revealed that CyA increased phospho-CaMKII, an active form of CaMKII. These findings suggest that CaN-dependent dephosphorylation inhibits CaMKII-mediated phosphorylation, and the inhibition of CaN increases phospho-CaMKII, which results in the stimulation of CaMKII-dependent cellular actions.