Transient increases in extracellular K+ produce two pharmacological distinct cytosolic Ca2+ transients

Responsiveness of voltage-gated calcium channels in SH-SY5Y human neuroblastoma cells on micropillar substrates

In this study, poly-L-lactic acid micropillar substrates were fabricated to evaluate the influence of topographic substrates on cell morphological and functional characteristics, such as spreading area, voltage-gated calcium channels (VGCCs) and membrane potential. The proliferation, spreading area, perimeter and circularity of SH-SY5Y cells interfaced with different substrates were first investigated. In addition, the cytoskeleton and focal adhesion of a cell as important manifestations of cell morphology were analyzed by immunofluorescence. VGCC responsiveness was evaluated by measuring the dynamic changes in intracellular Ca²⁺ evoked by 50 mM extracellular K⁺. To determine study whether the differences in VGCC responsiveness were caused by the differences in VGCC gene expression, the expression of N/L- type VGCCs was determined by qPCR and fluorescence staining. Notably, improved measurement of the membrane potential with potentiometric fluorescent dye TMRM was applied to determine the membrane potential of SH-SY5Y cells. Results indicated that the SH-SY5Y cells were deformed significantly to adapt to the substrates; however, no distinct effect on the proliferative ability of SH-SY5Y cells was observed. The micropillar substrates markedly influenced VGCC responsiveness, which correlated strongly with cell spreading but not with VGCC expression. The resting membrane potential of SH-SY5Y cells cultured on different substrates also changed, but no effect on responsiveness of VGCC was observed. These results suggest that the effect of the micropillar substrates on cell VGCC responsiveness may be attributed to changes in the functionality of the ion channel itself. Thus, topographic substrates can be used to engineer cell functionality in cell-based drug screening.

Negative neuronal differentiation of human adipose-derived stem cell clones

AIMS

Adipose mesenchymal stem cells are a heterogeneous population. Therefore, the question posed in this study is whether the heterogenic differentiation potential exhibited by the different clones toward mesodermic lineages can be extended to nonmesodermic lineages, such as the neuroectoderm.

MATERIALS & METHODS

Different single cell clones of human adipose mesenchymal stem cells from the same donor were isolated. Neuronal plasticity of the clones was assessed according to the pattern DNA methylation, gene expression and intracellular calcium responses.

RESULTS

Under neurogenic culture conditions, clones presented variable expression of neuronal-specific genes, but still expressed osteogenic markers. No calcium response was exhibited in response to KCl incubation. The DNA methylation profile presented a very similar pattern in neuroectoderm gene promoters.

CONCLUSIONS

Data indicate that there are no significant differences between the undifferentiated and supposedly neuronal-differentiated mesenchymal cells.

Potassium depolarization and raised calcium induces α-synuclein aggregates

α-Synuclein is the key aggregating protein in Parkinson's disease (PD), which is characterized by cytoplasmic protein inclusion bodies, termed Lewy bodies, thought to increase longevity of the host neuron by sequestering toxic soluble α-synuclein oligomers. Previous post-mortem studies have shown relative sparing of neurons in PD that are positive for the Ca(2+) buffering protein, calbindin, and recent cell culture and in vitro studies have shown that α-synuclein aggregation can be induced by Ca(2+). We hypothesized that depolarization with potassium resulting in raised Ca(2+) in a PD cell culture model will lead to the formation of α-synuclein protein aggregates and that the intracellular Ca(2+) buffer, BAPTA-AM, may suppress their formation. Live cell fluorescence microscopy was performed to monitor changes in intracellular free calcium in HEK293T, SH-SY5Y neuroblastoma or stably transfected HEK293T/α-synuclein cells. Raised intracellular free Ca(2+) was consistently observed in cells treated with KCl, but not controls. Immunohistochemistry analysis on cells 48-72 h after K(+) treatment revealed two subsets of cells with either large (>2 μm), perinuclear α-synuclein aggregates or multiple smaller (<2 μm), cytoplasmic accumulations. Cells pre-treated with varying concentrations of trimethadione (TMO), a calcium channel blocker, showed suppression of the Ca(2+) transient following KCl treatment and no α-synuclein aggregates at TMO concentrations >5 μM. Quantitative analysis revealed a significant increase in the number of cells bearing α-synuclein cytoplasmic inclusions in both HEK293T/α-synuclein and SHSY-5Y cells when transient intracellular raised Ca(2+) was induced (p = 0.001). BAPTA-AM pre-loading significantly suppressed α-synuclein aggregates (p = 0.001) and the intracellular free Ca(2+) transient. This study indicates that raised intracellular Ca(2+) mediated by K(+) depolarization can lead to α-synuclein aggregation.

The effects of extracellular calcium on motility, pseudopod and uropod formation, chemotaxis, and the cortical localization of myosin II in Dictyostelium discoideum

Extracellular Ca(++), a ubiquitous cation in the soluble environment of cells both free living and within the human body, regulates most aspects of amoeboid cell motility, including shape, uropod formation, pseudopod formation, velocity, and turning in Dictyostelium discoideum. Hence it affects the efficiency of both basic motile behavior and chemotaxis. Extracellular Ca(++) is optimal at 10 mM. A gradient of the chemoattractant cAMP generated in the absence of added Ca(++) only affects turning, but in combination with extracellular Ca(++), enhances the effects of extracellular Ca(++). Potassium, at 40 mM, can partially substitute for Ca(++). Mg(++), Mn(++), Zn(++), and Na(+) cannot. Extracellular Ca(++), or K(+), also induce the cortical localization of myosin II in a polar fashion. The effects of Ca(++), K(+) or a cAMP gradient do not appear to be similarly mediated by an increase in the general pool of free cytosolic Ca(++). These results suggest a model, in which each agent functioning through different signaling systems, converge to affect the cortical localization of myosin II, which in turn effects the behavioral changes leading to efficient cell motility and chemotaxis. Cell Motil. Cytoskeleton 2009. (c) 2009 Wiley-Liss, Inc.

Pulses of extracellular K+ produce two cytosolic Ca2+ transients that display different temperature dependence and carbonyl cyanide m-chlorophenyl sensitivity in SH-SY5Y cells

In SH-SY5Y cells we have shown that stimulation with high extracellular K+ ([K+]e) evokes a transient increase in cytoplasmic Ca2+ ([Ca2+]cyt) (K+on) that is triggered by the opening of voltage-dependent Ca2+ channels and followed by Ca2+ -induced Ca2+ release from the endoplasmic reticulum (Xu, F., Zhang, J., Recio-Pinto, E. and Blanck, T.J., Halothane and isoflurane augment depolarization-induced cytosolic CA2+ transients and attenuate carbachol-stimulated CA2+ transients, Anesthesiology, 92 (2000) 1746-56). The removal of high-[K+]e results in a second transient increase in [Ca2+]cyt (K+off) that is independent of extracellular Ca2+ (Corrales, A., Montoya, G.J., Sutachan, J.J., Cornillez-Ty, G., Garavito-Aguilar, Z., Xu, F., Blanck, T.J. and Recio-Pinto, E., Transient increases in extracellular K+ produce two pharmacological distinct cytosolic Ca2+ transients, Brain Res., 1031 (2005) 174-184). In this study we further characterize the properties of K+off. We found that K+off was detectable at near physiological temperatures (34-36 degrees C) but, depending on the level of [K+]e, it was undetectable or highly diminished at room temperature. In contrast, K+on was increased by lowering the temperature. Extracellular Na+ -replacement with K+ did not affect K+off, indicating that K+off was not generated by osmolarity changes. Replacement of extracellular Na+ with choline+ did not affect K+off, indicating that K+off did not result from activity changes of the plasma membrane Na+/Ca2+ exchanger. Caffeine decreased K+on but not K+off. CCCP (carbonyl cyanide m-chlorophenyl), a protonophore uncoupler that decreases mitochondrial Ca2+ uptake, decreased K+on but not K+off. CGP37157, an inhibitor of the mitochondria Na+/Ca2+ exchanger, decreased K+off when added alone but not when added simultaneously with CCCP. Clonazepam had similar effects as CGP37157. These findings indicate that the generation of K+off is strongly temperature-dependent and its pharmacology is distinct from the [Ca2+]cyt changes observed previously at room temperature.