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Permeable Channel (permeable + channel)

Distribution by Scientific Domains

Life Sciences	80%
Medical Sciences	20%

Selected Abstracts

Differentiation dependent expression of TRPA1 and TRPM8 channels in IMR-32 human neuroblastoma cells

JOURNAL OF CELLULAR PHYSIOLOGY, Issue 1 2009
Lauri M. Louhivuori
TRPA1 and TRPM8 are transient receptor potential (TRP) channels involved in sensory perception. TRPA1 is a non-selective calcium permeable channel activated by irritants and proalgesic agents. TRPM8 reacts to chemical cooling agents such as menthol. The human neuroblastoma cell line IMR-32 undergoes a remarkable differentiation in response to treatment with 5-bromo-2-deoxyuridine. The cells acquire a neuronal morphology with increased expression of N-type voltage gated calcium channels and neurotransmitters. Here we show using RT-PCR, that mRNA for TRPA1 and TRPM8 are strongly upregulated in differentiating IMR-32 cells. Using whole cell patch clamp recordings, we demonstrate that activators of these channels, wasabi, allyl-isothiocyanate (AITC) and menthol activate membrane currents in differentiated cells. Calcium imaging experiments demonstrated that AITC mediated elevation of intracellular calcium levels were attenuated by ruthenium red, spermine, and HC-030031 as well as by siRNA directed against the channel. This indicates that the detected mRNA level correlate with the presence of functional channels of both types in the membrane of differentiated cells. Although the differentiated IMR-32 cells responded to cooling many of the cells showing this response did not respond to TRPA1/TRPM8 channel activators (60% and 90% for AITC and menthol respectively). Conversely many of the cells responding to these activators did not respond to cooling (30%). This suggests that these channels have also other functions than cold perception in these cells. Furthermore, our results suggest that IMR-32 cells have sensory characteristics and can be used to study native TRPA1 and TRPM8 channel function as well as developmental expression. J. Cell. Physiol. 221: 67,74, 2009. © 2009 Wiley-Liss, Inc [source]

Identification of hyperpolarization-activated calcium channels in apical pollen tubes of Pyrus pyrifolia

NEW PHYTOLOGIST, Issue 3 2007
Hai-Yong Qu
Summary ,,The pollen tube has been widely used to study the mechanisms underlying polarized tip growth in plants. A steep tip-to-base gradient of free cytosolic calcium ([Ca2+]cyt) is essential for pollen-tube growth. Local Ca2+ influx mediated by Ca2+ -permeable channels plays a key role in maintaining this [Ca2+]cyt gradient. ,,Here, we developed a protocol for successful isolation of spheroplasts from pollen tubes of Pyrus pyrifolia and identified a hyperpolarization-activated cation channel using the patch-clamp technique. ,,We showed that the cation channel conductance displayed a strong selectivity for divalent cations, with a relative permeability sequence of barium (Ba2+) , Ca2+ > magnesium (Mg2+) > strontium (Sr2+) > manganese (Mn2+). This channel conductance was selective for Ca2+ over chlorine (Cl,) (relative permeability PCa/PCl = 14 in 10 mm extracellular Ca2+). We also showed that the channel was inhibited by the Ca2+ channel blockers lanthanum (La3+) and gadolinium (Gd3+). Furthermore, channel activity depended on extracellular pH and pollen viability. ,,We propose that the Ca2+ -permeable channel is likely to play a role in mediating Ca2+ influx into the growing pollen tubes to maintain the [Ca2+]cyt gradient. [source]

Identification of a putative voltage-gated Ca2+ channel as a key regulator of elicitor-induced hypersensitive cell death and mitogen-activated protein kinase activation in rice

THE PLANT JOURNAL, Issue 6 2005
Takamitsu Kurusu
Summary Elicitor-triggered transient membrane potential changes and Ca2+ influx through the plasma membrane are thought to be important during defense signaling in plants. However, the molecular bases for the Ca2+ influx and its regulation remain largely unknown. Here we tested effects of overexpression as well as retrotransposon (Tos17)-insertional mutagenesis of the rice two-pore channel 1 (OsTPC1), a putative voltage-gated Ca2+ -permeable channel, on a proteinaceous fungal elicitor-induced defense responses in rice cells. The overexpressor showed enhanced sensitivity to the elicitor to induce oxidative burst, activation of a mitogen-activated protein kinase (MAPK), OsMPK2, as well as hypersensitive cell death. On the contrary, a series of defense responses including the cell death and activation of the MAPK were severely suppressed in the insertional mutant, which was complemented by overexpression of the wild-type gene. These results suggest that the putative Ca2+ -permeable channel determines sensitivity to the elicitor and plays a role as a key regulator of elicitor-induced defense responses, activation of MAPK cascade and hypersensitive cell death. [source]

Functional characterization of TRPV4 as an osmotically sensitive ion channel in porcine articular chondrocytes

ARTHRITIS & RHEUMATISM, Issue 10 2009
Mimi N. Phan
Objective Transient receptor potential vanilloid 4 (TRPV4) is a Ca2+ -permeable channel that can be gated by tonicity (osmolarity) and mechanical stimuli. Chondrocytes, the cells in cartilage, respond to their osmotic and mechanical environments; however, the molecular basis of this signal transduction is not fully understood. This study was undertaken to demonstrate the presence and functionality of TRPV4 in chondrocytes. Methods TRPV4 protein expression was measured by immunolabeling and Western blotting. In response to TRPV4 agonist/antagonists, osmotic stress, and interleukin-1 (IL-1), changes in Ca2+ signaling, cell volume, and prostaglandin E2 (PGE2) production were measured in porcine chondrocytes using fluorescence microscopy, light microscopy, or immunoassay, respectively. Results TRPV4 was expressed abundantly at the RNA and protein levels. Exposure to 4,-phorbol 12,13-didecanoate (4,PDD), a TRPV4 activator, caused Ca2+ signaling in chondrocytes, which was blocked by the selective TRPV4 antagonist, GSK205. Blocking TRPV4 diminished the chondrocytes' response to hypo-osmotic stress, reducing the fraction of Ca2+ responsive cells, the regulatory volume decrease, and PGE2 production. Ca2+ signaling was inhibited by removal of extracellular Ca2+ or depletion of intracellular stores. Specific activation of TRPV4 restored the defective regulatory volume decrease caused by IL-1. Chemical disruption of the primary cilium eliminated Ca2+ signaling in response to either 4,PDD or hypo-osmotic stress. Conclusion Our findings indicate that TRPV4 is present in articular chondrocytes, and chondrocyte response to hypo-osmotic stress is mediated by this channel, which involves both an extracellular Ca2+ and intracellular Ca2+ release. TRPV4 may also be involved in modulating the production or influence of proinflammatory molecules in response to osmotic stress. [source]

Genistein potentiates activity of the cation channel TRPC5 independently of tyrosine kinases

BRITISH JOURNAL OF PHARMACOLOGY, Issue 7 2010
Ching-On Wong
Background and purpose:, TRPC5 is a Ca2+ -permeable channel with multiple modes of activation. We have explored the effects of genistein, a plant-derived isoflavone, on TRPC5 activity, and the mechanism(s) involved. Experimental approach:, Effects of genistein on TRPC5 channels were investigated in TRPC5-over-expressing human embryonic kidney 293 (HEK) cells and bovine aortic endothelial cells (BAECs) using fluorescent Ca2+ imaging and electrophysiological techniques. Key results:, In TRPC5-over-expressing HEK cells, genistein stimulated TRPC5-mediated Ca2+ influx, concentration dependently (EC50= 93 µM). Genistein and lanthanum activated TRPC5 channels synergistically. Effects of genistein on TRPC5 channels were mimicked by daidzein (100 µM), a genistein analogue inactive as a tyrosine kinase inhibitor, but not by known tyrosine kinase inhibitors herbimycin (2 µM), PP2 (20 µM) and lavendustin A (10 µM). Action of genistein on TRPC5 channels was not affected by an oestrogen receptor inhibitor ICI-182780 (50 µM) or a phospholipase C inhibitor U73122 (10 µM), suggesting genistein did not act through oestrogen receptors or phospholipase C. In BAECs, genistein (100 µM) stimulated TRPC5-mediated Ca2+ influx. In patch clamp studies, both genistein (50 µM) and daidzein (50 µM) augmented TRPC5-mediated whole-cell cation current in TRPC5 over-expressing HEK cells. Genistein stimulated TRPC5 channel activity in excised inside-out membrane patch, suggesting that its action was relatively direct and did not require cytosolic factors. Conclusions and implications:, The present study is the first to demonstrate stimulation of a TRP channel by isoflavones. Genistein is a lipophilic compound able to stimulate TRPC5 activity in TRPC5-over-expressing HEK cells and in native vascular endothelial cells. [source]

Identification of hyperpolarization-activated calcium channels in apical pollen tubes of Pyrus pyrifolia

NaCl-induced changes in cytosolic free Ca2+ in Arabidopsis thaliana are heterogeneous and modified by external ionic composition

PLANT CELL & ENVIRONMENT, Issue 8 2008
FRANCES E. TRACY
ABSTRACT Increases in cytosolic free Ca2+ ([Ca2+]cyt) are common to many stress-activated signalling pathways, including the response to saline environments. We have investigated the nature of NaCl-induced [Ca2+]cyt signals in whole Arabidopsis thaliana seedlings using aequorin. We found that NaCl-induced increases in [Ca2+]cyt are heterogeneous and mainly restricted to the root. Both the concentration of NaCl and the composition of the solution bathing the root have profound effects on the magnitude and dynamics of NaCl-induced increases in [Ca2+]cyt. Alteration of external K+ concentration caused changes in the temporal and spatial pattern of [Ca2+]cyt increase, providing evidence for Na+ -induced Ca2+ influx across the plasma membrane. The effects of various pharmacological agents on NaCl-induced increases in [Ca2+]cyt indicate that NaCl may induce influx of Ca2+ through both plasma membrane and intracellular Ca2+ -permeable channels. Analysis of spatiotemporal [Ca2+]cyt dynamics using photon-counting imaging revealed additional levels of complexity in the [Ca2+]cyt signal that may reflect the oscillatory nature of NaCl-induced changes in single cells. [source]

Ca2+ microdomains near plasma membrane Ca2+ channels: impact on cell function

THE JOURNAL OF PHYSIOLOGY, Issue 13 2008
Anant B. Parekh
In eukaryotic cells, a rise in cytoplasmic Ca2+ can activate a plethora of responses that operate on time scales ranging from milliseconds to days. Inherent to the use of a promiscuous signal like Ca2+ is the problem of specificity: how can Ca2+ activate some responses but not others? We now know that the spatial profile of the Ca2+ signal is important Ca2+ does not simply rise uniformly throughout the cytoplasm upon stimulation but can reach very high levels locally, creating spatial gradients. The most fundamental local Ca2+ signal is the Ca2+ microdomain that develops rapidly near open plasmalemmal Ca2+ channels like voltage-gated L-type (Cav1.2) and store-operated CRAC channels. Recent work has revealed that Ca2+ microdomains arising from these channels are remarkably versatile in triggering a range of responses that differ enormously in both temporal and spatial profile. Here, I delineate basic features of Ca2+ microdomains and then describe how these highly local signals are used by Ca2+ -permeable channels to drive cellular responses. [source]

,-Latrotoxin increases spontaneous and depolarization-evoked exocytosis from pancreatic islet ,-cells

THE JOURNAL OF PHYSIOLOGY, Issue 3 2005
Amelia M. Silva
,-Latrotoxin (,-LT), a potent excitatory neurotoxin, increases spontaneous, as well as action potential-evoked, quantal release at nerve terminals and increases hormone release from excitable endocrine cells. We have investigated the effects of ,-LT on single human, mouse and canine ,-cells. In isolated and combined measurements, ,-LT, at nanomolar concentrations, induces: (i) rises in cytosolic Ca2+, into the micromolar range, that are dependent on extracellular Ca2+; (ii) large conductance non-selective cation channels; and (iii) Ca2+ -dependent insulin granule exocytosis, measured as increases in membrane capacitance and quantal release of preloaded serotonin. Furthermore, at picomolar concentrations, ,-LT potentiates depolarization-induced exocytosis often without evidence of inducing channel activity or increasing cytosolic Ca2+. These results strongly support the hypothesis that ,-LT, after binding to specific receptors, has at least two complementary modes of action on excitable cells. (i) ,-LT inserts into the plasma membrane to form Ca2+ permeable channels and promote Ca2+ entry thereby triggering Ca2+ -dependent exocytosis in unstimulated cells. (ii) At lower concentrations, where its channel forming activity is hardly evident, ,-LT augments depolarization-evoked exocytosis probably by second messenger-induced enhancement of the efficiency of the vesicle recruitment or vesicle fusion machinery. We suggest that both modes of action enhance exocytosis from a newly described highly Ca2+ -sensitive pool of insulin granules activated by global cytosolic Ca2+ concentrations in the range of ,1 ,m. [source]

Plant extracellular ATP signalling by plasma membrane NADPH oxidase and Ca2+ channels

THE PLANT JOURNAL, Issue 6 2009
Vadim Demidchik
Summary Extracellular ATP regulates higher plant growth and adaptation. The signalling events may be unique to higher plants, as they lack animal purinoceptor homologues. Although it is known that plant cytosolic free Ca2+ can be elevated by extracellular ATP, the mechanism is unknown. Here, we have studied roots of Arabidopsis thaliana to determine the events that lead to the transcriptional stress response evoked by extracellular ATP. Root cell protoplasts were used to demonstrate that signalling to elevate cytosolic free Ca2+ is determined by ATP perception at the plasma membrane, and not at the cell wall. Imaging revealed that extracellular ATP causes the production of reactive oxygen species in intact roots, with the plasma membrane NADPH oxidase AtRBOHC being the major contributor. This resulted in the stimulation of plasma membrane Ca2+ -permeable channels (determined using patch-clamp electrophysiology), which contribute to the elevation of cytosolic free Ca2+. Disruption of this pathway in the AtrbohC mutant impaired the extracellular ATP-induced increase in reactive oxygen species (ROS), the activation of Ca2+ channels, and the transcription of the MAP kinase3 gene that is known to be involved in stress responses. This study shows that higher plants, although bereft of purinoceptor homologues, could have evolved a distinct mechanism to transduce the ATP signal at the plasma membrane. [source]