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H F Li

Publications and source records attributed to H F Li.

At least 37 records · Page 2Linked to original sources
PubMed2001

[Environmental investigation in areas where Anopheles anthropophagus distributed in Hubei Province].

OBJECTIVE: To investigate the natural and socio-economical environment in the areas where Anopheles anthropophagus distributed in Hubei Province. METHODS: 5% of the villages in distribution area of An. anthropophagus were randomly selected for the investigation which included vegetation, soil, water, temperature, farming, resting places of the mosquito. RESULTS: The vegetation of An. anthropophagus area consisted of forest, bush, sod and crops. The area was densely covered with river, ditches and ponds, the water pH being 6.1-7.7. The soil texture was either yellow, yellow brown, grey or black, contained 2.72% organic material. There were one or two seasons of rice plantation in the area and the amount of insecticide used was 0.828 kg/mu in the rice field. The annual average temperature was 16.9 degrees C and the humidity was 76.9%. The breed period of An. anthropophagus was from June to September. There are two peaks of mosquito population in area with two seasons of rice plantation, and one peak in one rice season. The composition of An. anthropophagus resting in households, cowsheds and pigpens was 80.9%, 12.2% and 6.0%, respectively. CONCLUSION: The distribution of An. anthropophagus was in point, flaky or belt form in low hill, hillock, shallow hilly plain. These areas were full of vegetation and source of water, the principal crop was single cropping of rice, and soil texture is yellow or yellow brown. The major resting place of the mosquito was human dwellings.

Animals↗
PubMed2000

Characterization of ATP-sensitive potassium channels functionally expressed in pituitary GH3 cells.

ATP-sensitive K+ (KATP) channels have been characterized in pituitary GH3 cells with the aid of the patch-clamp technique. In the cell-attached configuration, the presence of diazoxide (100 microM) revealed the presence of glibenclamide-sensitive KATP channel exhibiting a unitary conductance of 74 pS. Metabolic inhibition induced by 2,4-dinitrophenol (1 mM) or sodium cyanide (300 microM) increased KATP channel activity, while nicorandil (100 microM) had no effect on it. In the inside-out configuration, Mg-ATP applied intracellularly suppressed the activity of KATP channels in a concentration-dependent manner with an IC50 value of 30 microM. The activation of phospholipase A2 caused by mellitin (1 microM) was found to enhance KATP channel activity and further application of aristolochic acid (30 microM) reduced the mellitin-induced increase in channel activity. The challenging of cells with 4,4'-dithiodipyridine (100 microM) also induced KATP channel activity. Diazoxide, mellitin and 4,4'-dithiodipyridine activated the KATP channels that exhibited similar channel-opening kinetics. In addition, under current-clamp conditions, the application of diazoxide (100 microM) hyperpolarized the membrane potential and reduced the firing rate of spontaneous action potentials. The present study clearly indicates that KATP channels similar to those seen in pancreatic beta cells are functionally expressed in GH3 cells. In addition to the presence of Ca(2+)-activated K+ channels, KATP channels found in these cells could thus play an important role in controlling hormonal release by regulating the membrane potential.

2,4-Dinitrophenol↗
PubMed2000

The mechanism of actions of 3-(5'-(hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1) on Ca(2+)-activated K(+) currents in GH(3) lactotrophs.

The effects of 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1), an activator of soluble guanylyl cyclase, on ionic currents have been assessed in rat pituitary GH(3) lactotrophs. In GH(3) cells bathed in normal Tyrode's solution, YC-1 (1 microM) reversibly suppressed the amplitude of the Ca(2+)-activated K(+) current (I(K(Ca))). YC-1 at a concentration above 10 microM produced a biphasic response in the amplitude of I(K(Ca)), i.e., an initial decrease followed by a sustained increase. When the pipette solutions were filled with high EGTA (10 mM), the YC-1-induced stimulatory effect on I(K(Ca)) was abolished. Over a similar concentration range, YC-1 also effectively inhibited the voltage-dependent K(+) current (I(K(V))) in GH(3) cells. The IC(50) value required for the inhibition of I(K(V)) by YC-1 was 1 microM. Unlike YC-1, 8-bromo cGMP did not inhibit I(K(Ca)). However, YC-1 (10 microM) did not affect the amplitude of L-type Ca(2+) current. In the cell-attached configuration, application of YC-1 (10 microM) to the bath did not change the single-channel conductance of the large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels; however, it did increase the opening probability of BK(Ca) channels. In contrast, in the outside-out configuration, YC-1 (10 microM) significantly suppressed the opening probability of BK(Ca) channels. The present study shows dual effects of YC-1 on I(K(Ca)) in GH(3) cells. The YC-1-mediated stimulation of I(K(Ca)) may result from elevated cytosolic Ca(2+), whereas the inhibition of I(K(Ca)) and I(K(V)) by YC-1 appears to be direct and independent of the activation of soluble guanylyl cyclase. Caution thus needs to be used in attributing the YC-1-mediated response to the activation of soluble guanylyl cyclase.

Animals↗
PubMed2000

Actions of epoxyeicosatrienoic acid on large-conductance Ca(2+)-activated K(+) channels in pituitary GH(3) cells.

Epoxyeicosatrienoic acids (EETs), a family of cytochrome P450 epoxygenase metabolites of arachidonic acid, are believed to have an autocrine or paracrine role in the regulation of neurons or neuroendocrine cells. The effects of 14,15-EET on ionic currents were investigated in rat pituitary GH(3) cells. In the whole-cell configuration, 14,15-EET (3 microM) reversibly increased the amplitude of the Ca(2+)-activated K(+) current (I(K(Ca))). The 14, 15-EET-induced increase in I(K(Ca)) was unaffected in the presence of 10 microM thyrotropin-releasing hormone externally or 10 microM inositol trisphosphate in the recording pipette. In cells preincubated with pertussis toxin or herbimycin A, the 14, 15-EET-induced increase in I(K(Ca)) was also not changed. In the inside-out configuration, 14,15-EET applied intracellularly did not change single-channel conductance, but did increase the opening probability of large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels. 14,15-EET (3 microM) shifted the activation curve of BK(Ca) channels to less positive membrane potential by approximately 15 mV. The change in the kinetic behavior of BK(Ca) channels caused by 14,15-EET is explained by a lengthening of open and a shortening of closed times. 14,15-EET increased the activity of BK(Ca) channels in a concentration-dependent manner with an EC(50) value of 1 microM. However, 14,15-EET did not affect the Ca(2+) sensitivity of BK(Ca) channels. The present study indicates that 14,15-EET is an opener of BK(Ca) channels in GH(3) cells and that the stimulatory effect of 14, 15-EET on these channels may, at least in part, contribute to the underlying cellular mechanisms by which EETs affect neuronal or neuroendocrine function.

8,11,14-Eicosatrienoic Acid↗
PubMed2000

Evidence for the stimulatory effect of resveratrol on Ca(2+)-activated K+ current in vascular endothelial cells.

OBJECTIVE: Resveratrol, a natural phytoalexin compound, is present in grapes and wine, and it can produce vasorelaxation. However, little is known of its mechanisms of action on ionic currents in endothelial cells. METHODS: The effect of resveratrol on Ca(2+)-activated K+ currents in an endothelial cell line (HUV-EC-C) originally derived from human umbilical vein was investigated with the aid of the patch-clamp technique. RESULTS: In the whole-cell configuration, resveratrol reversibly increased the amplitude of K+ outward currents. The increase in outward current caused by resveratrol was greatly inhibited by iberiotoxin (200 nM) or paxilline (1 microM), but not by glibenclamide (10 microM), tamoxifen (10 microM), or beta-bungarotoxin (200 nM). Thus, this outward current is believed to be Ca(2+)-activated K+ current (I K(Ca)). In the inside-out configuration, bath application of resveratrol (30 microM) caused no change in the single-channel conductance, but increased the activity of large-conductance Ca(2+)-activated K+ (BKCa) channels. Resveratrol enhanced the channel activity in a concentration-dependent manner. The EC50 value for resveratrol-induced channel activity was 20 microM. The resveratrol-stimulated increase in the channel activity was independent of internal Ca2+. Resveratrol (30 microM) also shifted the activation curve of BKCa channels to less positive membrane potentials. The change in the kinetic behavior of BKCa channels caused by resveratrol in these cells in due to an increase in mean open time and a decrease in mean closed time. In a pancreatic islet endothelial cell line (MS1), resveratrol (30 microM) also increased the activity of intermediate-conductance KCa channels. CONCLUSIONS: These results provide evidence that in addition to the presence of antioxidative activity, resveratrol can also stimulate KCa channels in endothelial cells. The direct stimulation of these KCa channels by resveratrol may be responsible for its effect on the functional activities of endothelial cells.

Cell Line↗
PubMed2000

Characterization of inhibition by risperidone of the inwardly rectifying K(+) current in pituitary GH(3) cells.

The effects of risperidone on ionic currents in rat pituitary GH(3) cells were investigated with the aid of the patch-clamp technique. Hyperpolarization-activated K(+) currents in GH(3) cells bathed in high-K(+) Ca(2+)-free solution were studied to determine the effect of risperidone and other related compounds on the inwardly rectifying K(+) current (I(K(IR))). Risperidone (0.1-10 microM) suppressed the amplitude of I(K(IR)) in a concentration-dependent manner. The IC(50) value for the risperidone-induced inhibition of I(K(IR)) was 1 microM. Risperidone (3 microM) was found to slow the rate of activation. An increase in current deactivation by the presence of risperidone was also observed. Haloperidol (10 microM) and thioridazine (10 microM) inhibited the amplitude of I(K(IR)) effectively, and clozapine slightly suppressed it; however, metoclopramide (10 microM) had no effect on it. Risperidone (10 microM) had no effect on voltage-dependent K(+) and L-type Ca(2+) currents. However, in the inside-out configuration, risperidone (10 microM) did not alter the single-channel conductance, but reduced the activity of large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels. Under the current-clamp mode, risperidone (3 microM) depolarized the membrane potential and increased the firing rate. With the aid of the spectral analysis, cells that exhibited an irregular firing pattern were also converted to those displaying a regular firing pattern after addition of risperidone (3 microM). The present study provides evidence that risperidone, in addition to the blockade of dopamine receptors, can produce a depressant effect on I(K(IR)) and BK(Ca) channels, and implies that the blockade of these ionic currents by risperidone may affect membrane excitability and prolactin secretion in GH(3) cells.

Action Potentials↗
PubMed2000

Plant genetics affects arthropod community richness and composition: evidence from a synthetic eucalypt hybrid population.

To examine how genetic variation in a plant population affects arthropod community richness and composition, we quantified the arthropod communities on a synthetic population of Eucalyptus amygdalina, E. risdonii, and their F1 and advanced-generation hybrids. Five major patterns emerged. First, the pure species and hybrid populations supported significantly different communities. Second, species richness was significantly greatest on hybrids (F1 > F2 > E. amygdalina > E. risdonii). These results are similar to those from a wild population of the same species and represent the first case in which both synthetic and wild population studies confirm a genetic component to community structure. Hybrids also acted as centers of biodiversity by accumulating both the common and specialist taxa of both parental species (100% in the wild and 80% in the synthetic population). Third, species richness was significantly greater on F1s than the single F2 family, suggesting that the increased insect abundance on hybrids may not be caused by the breakup of coadapted gene complexes. Fourth, specialist arthropod taxa were most likely to show a dominance response to F1 hybrids, whereas generalist taxa exhibited a susceptible response. Fifth, in an analysis of 31 leaf terpenoids that are thought to play a role in plant defense, hybrids were generally intermediate to the parental chemotypes. Within the single F2 family, we found significant associations between the communities of individual trees and five individual oil components, including oil yield, demonstrating that there is a genetic effect on plant defensive chemistry that, in turn, may affect community structure. These studies argue that hybridization has important community-level consequences and that the genetic variation present in hybrid zones can be used to explore the genetic-based mechanisms that structure communities.

Animals↗
PubMed2000

Characterization of tetrandrine-induced inhibition of large-conductance calcium-activated potassium channels in a human endothelial cell line (HUV-EC-C).

The effects of tetrandrine, a blocker of voltage-dependent Ca(2+) channels, on ionic currents were investigated in an endothelial cell line (HUV-EC-C) originally derived from human umbilical vein. In whole-cell configuration, tetrandrine (0.5-50 microM) reversibly decreased the amplitude of K(+) outward currents. The IC(50) value of tetrandrine-induced decrease in outward current was 5 microM. The K(+) outward current in response to depolarizing voltage pulses was also inhibited by iberiotoxin (200 nM), yet not by glibenclamide (10 microM) or apamin (200 nM). The reduced amplitude of outward current by tetrandrine can be reversed by the further addition of Evans' blue (30 microM) or niflumic acid (30 microM). Thus, the tetrandrine-sensitive component of outward current is believed to be Ca(2+)-activated K(+) current. Pretreatment with thapsigargin (1 microM) or sodium nitroprusside (10 microM) for 5 h did not prevent tetrandrine-mediated inhibition of outward current. In outside-out configuration, bath application of tetrandrine (5 microM) did not change the single-channel conductance but significantly reduced the opening probability of large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels. The tetrandrine-mediated decrease in the channel activity was independent on internal Ca(2+) concentration. Tetrandrine (5 microM) can also shift the activation curve of BK(Ca) channels to more positive potentials by approximately 20 mV. The change in the kinetic behavior of BK(Ca) channels caused by tetrandrine is due to a decrease in mean open time and an increase in mean closed time. The present study provides substantial evidence that tetrandrine is capable of suppressing the activity of BK(Ca) channels in endothelial cells. The direct inhibition of these channels by tetrandrine should contribute to its effect on the functional activities of endothelial cells.

Alkaloids↗
PubMed2000

Stimulatory effects of delta-hexachlorocyclohexane on Ca(2+)-activated K(+) currents in GH(3) lactotrophs.

delta-Hexachlorocyclohexane (delta-HCH), a lipophilic neurodepressant agent, has been shown to inhibit neurotransmitter release and stimulate ryanodine-sensitive Ca(2+) channels. However, the effect of delta-HCH on neuronal activity remains unclear, although it may enhance the gamma-aminobutyric acid-induced current. Its effects on ionic currents were investigated in rat pituitary GH(3) cells and human neuroblastoma IMR-32 cells. In GH(3) cells, delta-HCH increased the amplitude of Ca(2+)-activated K(+) current (I(K(Ca))). delta-HCH (100 microM) slightly inhibited the amplitude of voltage-dependent K(+) current. delta-HCH (30 microM) suppressed voltage-dependent L-type Ca(2+) current (I(Ca, L)), whereas gamma-HCH (30 microM) had no effect on I(Ca, L). In the inside-out configuration, delta-HCH applied intracellularly did not change the single channel conductance of large conductance Ca(2+)-activated K(+) (BK(Ca)) channels; however, it did increase the channel activity. The delta-HCH-mediated increase in the channel activity is mainly mediated by its increase in the number of long-lived openings. delta-HCH reversibly increased the activity of BK(Ca) channels in a concentration-dependent manner with an EC(50) value of 20 microM. delta-HCH also caused a left shift in the midpoint for the voltage-dependent opening. In contrast, gamma-HCH (30 microM) suppressed the activity of BK(Ca) channels. Under the current-clamp mode, delta-HCH (30 microM) reduced the firing rate of spontaneous action potentials; however, gamma-HCH (30 microM) increased it. In neuroblastoma IMR-32 cells, delta-HCH also increased the amplitude of I(K(Ca)) and stimulated the activity of intermediate-conductance K(Ca) channels. This study provides evidence that delta-HCH is an opener of K(Ca) channels. The effects of delta-HCH on these channels may partially, if not entirely, be responsible for the underlying cellular mechanisms by which delta-HCH affects neuronal or neuroendocrine function.

Action Potentials↗
PubMed2000

Regulation of Ca(2+)-activated K+ currents by ciglitazone in rat pituitary GH3 cells.

BACKGROUND: Ciglitazone, an antidiabetic agent of the thiazolidinedione family, is known to be an activator of the peroxisome-proliferator activator receptor (PPAR)-gamma. The underlying mechanism of ciglitazone actions on ionic currents in neuroendocrine cells remains unclear. METHODS: The effects of ciglitazone on ionic currents were investigated in rat pituitary GH3 cells using the whole-cell and inside-out configurations of the patch-clamp technique. RESULTS: In GH3 cells, ciglitazone at 3-300 mumol/L caused a reversible increase in the amplitude of the Ca(2+)-activated K+ current (IK(Ca)) with a half-maximal concentration of 16 mumol/L. Under the inside-out patch recording mode, ciglitazone applied intracellularly increased the activity of the large-conductance Ca(2+)-activated K+ (BKCa) channels, but did not affect their single-channel conductance. However, troglitazone (30 mumol/L) caused a reduction in the channel activity. The ciglitazone-induced change in the kinetic behavior of BKCa channels is due to an increase in mean open time and a decrease in mean closed time, whereas the troglitazone-induced decrease in the channel activity is related to a decrease in mean open time and an increase in mean closed time. Ciglitazone caused a left shift in the midpoint for voltage-dependent opening. The ciglitazone-stimulated activity of BKCa channels is independent of internal Ca2+. Under the current clamp mode, ciglitazone (30 mumol/L) hyperpolarized the membrane potential. CONCLUSIONS: This study shows that in addition to its activation of PPAR-gamma, ciglitazone can stimulate the activity of BKCa channels expressed in GH3 cells. These effects may affect membrane potentials and contribute to the ciglitazone-induced change in the functional activity of neurons or neuroendocrine cells.

Adenosine Triphosphate↗
PubMed1999

Stimulation of large-conductance Ca2+-activated K+ channels by Evans blue in cultured endothelial cells of human umbilical veins.

The effect of Evans blue (EB) on large-conductance Ca2+-activated K+ (BKCa) channels was investigated in cultured endothelial cells of human umbilical veins. In whole-cell configuration, EB (50 microM) reversibly increased the amplitude of K+ outward currents (IK). When the patch pipettes were filled with 10 mM EGTA, its stimulatory effect on IK was unaltered. Further application of EB in the presence of suramin, a blocker of P2-purinergic receptor, or AOPCP, an inhibitor of 5'-nucleotidase, still increased IK. However, charybdotoxin (100 nM) suppressed EB-induced increase in IK. In inside-out configuration, bath application of EB (50 microM) did not change single channel conductance but significantly increased the activity of BKCa channels. The EB-induced increase in the activity of BKCa channels was independent on internal Ca2+. EB (50 microM) shifted the activation curve of BKCa channels to less positive membrane potentials by approximately 20 mV. The change in the kinetic behavior of BKCa channels caused by EB in these cells is due to an increase in mean open time and a decrease in mean closed time. These results indicate that EB can stimulate the activity of BKCa channel in endothelial cells. This effect is unrelated to its blockade of P2-purinergic receptors or inhibition of 5'-nucleotidase. The direct stimulation of these ionic channels by EB may contribute to its effect on capillary permeability.

Adenosine Diphosphate↗
PubMed1999

Inhibition of Ca2+-activated K+ current by clotrimazole in rat anterior pituitary GH3 cells.

The ionic mechanism of clotrimazole, an imidazole antimycotic P-450 inhibitor, was examined in rat anterior pituitary GH3 cells. In perforated-patch whole-cell recording experiments, clotrimazole reversibly caused an inhibition of the Ca2+-activated K+ current in a dose-dependent manner. The IC50 value of the clotrimazole-induced inhibition of I(K(Ca)) was 3 microM. In the outside-out configuration of single channel recording, application of clotrimazole (10 microM) into the bath medium did not change the single channel conductance of large conductance Ca2+-activated K+(BK(Ca)) channels, but it suppressed the channel activity significantly. The change in the kinetic behavior of BK(Ca) channels caused by clotrimazole in these cells is found to be due to a decrease in mean open time and an increase in mean closed time. Other structurally distinct P-450 inhibitors (e.g. ketoconazole or econazole) also effectively suppressed the amplitude of I(K(Ca)). Clotrimazole (10 microM) blocked both the inactivating and non-inactivating components of the voltage-dependent K+ outward current (I(K(V))), but it produced a slight reduction of L-type Ca2+ inward current (I(Ca,L)) without altering the current-voltage relationship of I(Ca,L). Clotrimazole (10 microM) also increased the firing rate of action potentials. These results provide direct evidence that clotrimazole is capable of suppressing the activity of BK(Ca) channel in GH3 cells. Because of the non-selective inhibitory effect of clotrimazole on I(K(Ca)) and I(K(V)), this inhibition is mainly, if not entirely, due to a direct channel blockade. Thus, the present study implies that the blockade of these ionic channels by clotrimazole would affect hormonal secretion and neuronal excitability.

Action Potentials↗
PubMed1999

Ruthenium red-mediated inhibition of large-conductance Ca2+-activated K+ channels in rat pituitary GH3 cells.

The ionic mechanism of actions of ruthenium red was examined in rat anterior pituitary GH(3) cells. In whole-cell recording experiments, ruthenium red reversibly caused an inhibition of Ca(2+)-activated K(+) current [I(K(Ca))] in a dose-dependent manner. The IC(50) value of ruthenium red-induced inhibition of I(K(Ca)) was 15 microM. Neither carbonyl cyanide m-chlorophenyl hydrazone (CCCP; 10 microM), an uncoupler of oxidative phosphorylation in mitochondria, nor cyclosporin A (200 nM), an inhibitor of the mitochondrial permeability transition pore, affected the amplitude of I(K(Ca)). In inside-out configuration, application of ruthenium red (50 microM) into the bath medium did not change single-channel conductance but significantly suppressed the activity of large-conductance Ca(2+)-activated K(+) channel (BK(Ca)) channels. The ruthenium red-induced decrease in the channel activity of BK(Ca) channels was reversed by an increase in intracellular Ca(2+) concentration. Ruthenium red also shifted the activation curve of BK(Ca) channels to positive membrane potentials. The change in the kinetic behavior of BK(Ca) channels caused by ruthenium red in these cells is due to a decrease in mean open time and an increase in mean closed time. Ruthenium red (50 microM) did not affect the amplitude of voltage-dependent K(+) current but produced a significant reduction of voltage-dependent L-type Ca(2+) current. These results indicate that ruthenium red can directly suppress the activity of BK(Ca) channels in GH(3) cells. This effect is independent on the inhibition of Ca(2+) release from internal stores or mitochondria.

4-Aminopyridine↗
PubMed1999

Characterization of riluzole-induced stimulation of large-conductance calcium-activated potassium channels in rat pituitary GH3 cells.

BACKGROUND: Riluzole is known to be an inhibitor of glutamatergic neurotransmission. Transmitter release from nerve terminals can be regulated by the activity of large-conductance Ca(2+)-activated K+(BKCa) channels. METHODS: The ionic mechanism of actions of riluzole was investigated in neuroendocrine (GH3 and PC12 cells), using the whole-cell patch-clamp and inside-out excised patch configurations. RESULTS: In GH3 cells, riluzole at 0.3-100 mumol/L increased the amplitude of Ca(2+)-activated K+ current (IK(Ca)) in a concentration-dependent manner with a half maximal concentration of 5 mumol/L. The riluzole-induced increase in outward current was not be suppressed by glibenclamide (10 mumol/L) or apamin (200 nmol/L). However, iberiotoxin (200 nmol/L) or tetrandrine (10 mumol/L) can effectively suppress riluzole-induced IK(Ca). Under inside-out patch recording mode, riluzole (10 mumol/L) applied intracellularly can increase the opening probability of large-conductance Ca(2+)-activated K+(BKCa) channels, but did not affect their single-channel conductance. The riluzole-induced change in the kinetic behavior of BKCa channels is due to an increase in mean open time and a decrease in mean closed time. Riluzole caused a left shift in the midpoint for voltage-dependent opening. Riluzole-stimulated activity of BKCa is independent on internal Ca2+. Riluzole (30 mumol/L) did not affect the amplitude of voltage-dependent K+ current, but it produced a slight reduction of L-type voltage-dependent Ca2+ current. Under current clamp mode, riluzole (10 mumol/L) decreased the firing rate of action potentials induced by thyrotropin releasing hormone (10 mumol/L) in GH3 cells. In rat pheochromocytoma PC12 cells, riluzole also increased the activity of BKCa channels without altering their channel conductance. CONCLUSION: This study shows that riluzole can stimulate the activity of BKCa channel in neuroendocrine cells.

Animals↗
PubMed1998

Regulation of Ca2+-activated nonselective cationic currents in rat pituitary GH3 cells: involvement in L-type Ca2+ current.

Ionic currents were investigated by a patch clamp technique in a clonal strain of pituitary (GH3) cells, using the whole cell configuration with Cs+ internal solution. Depolarizing pulses positive to 0 mV from a holding potential of -50 mV activated the voltage-dependent L-type Ca2+ current (ICa,L) and late outward current. Upon repolarization to the holding potential, a slowly decaying inward tail current was also observed. This inward tail current upon repolarization following a depolarizing pulse was found to be enhanced by Bay K 8644, but blocked by nifedipine or tetrandrine. This current was eliminated by Ba2+ replacement of external Ca2+ as the charge carrier through Ca2+ channels, removal of Ca2+ from the bath solution, or buffering intracellular Ca2+ with EGTA (10 mM). The reversal potential of inward tail current was approximately -25 mV. When intracellular Cl- was changed, the reversal potential of the Ca2+-activated currents was not shifted. Thus, this current is elicited by depolarizing pulses that activate ICa,L and allow Ca2+ influx, and is referred to as Ca2+-activated nonselective cationic current (ICAN). Without including EGTA in the patch pipette, the slowly decaying inward current underlying the long-lasting depolarizing potential after Ca2+ spike was also observed with a hybrid current-voltage protocol. Thus, the present studies clearly indicate that Ca2+-activated nonselective cationic channels are expressed in GH3 cells, and can be elicited by the depolarizing stimuli that lead to the activation of ICa,L.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1998

Co-activation of nonselective cation channels by store depletion and oxidative stress in monocytic U937 cells.

Two different types of nonselective cation currents in monocytic U937 cells were characterized with the aid of patch-clamp technique. When the cells were exposed to oxidative stress with 10 mM H2O2, a nonselective cation current (INS) can be elicited. This current was still observed when extracellular cations are Ca2+. The change in intracellular Cl- concentrations did not shift the reversal potential of this current. This current showed no any rectification, and was time- and voltage-independent at any potentials. The further addition of LaCl3 (100 microM) or dithiothreitol (10 microM) effectively suppressed this current. However, SK & F 96365 (100 microM) or nifedipine (10 microM) did not produce any effect on it significantly. On the other hand, depletion of Ca2+ stores by different maneuvers, such as the application of ATP, thapsigargin or A23187, or dialysis of the cells with inositol-1,4,5-trisphosphate activated another type of nonselective current which was identified as store-operated Ca(2+)-permeable current (ISOC). Unlike H2O2-induced INS, this current was observed to slowly inactivate when the voltage steps were hyperpolarized. Current-voltage relation of this current showed inward rectification. When the cell was challenged with both store depletion and H2O2, INS on the top of ISOC can be activated. These results suggest that different types of nonselective cation channels can be co-expressed in the same cell. Therefore, in U937 cells nonselective cation currents can be activated after the stimulation with oxidative stress, store depletion or both. The activation of these nonselective cation channels may affect intracellular Ca2+ homeostasis.

Biotransformation↗
PubMed1998

Inhibitory effects of berberine on voltage- and calcium-activated potassium currents in human myeloma cells.

The effects of berberine, an isoquinoline alkaloid, were investigated in human myeloma cells. In cells with intracellular Ca2+ concentration ([Ca2+]i) = 10 nM, the depolarizing square pulses from -80 mV elicited an instantaneous outward current with an inactivation. This outward current was voltage dependent, activating at -30 mV and showed inactivation with repetitive depolarization, and was hence believed to be n type voltage-activated K+ current (IK(V)). Berberine (30 microM) produced a prolongation in the recovery of IK(V) inactivation. In cells with [Ca2+]i = 1 microM, berberine also inhibited A23187-induced IK(Ca). Berberine (1-300 microM) caused the inhibition of IK(V) and IK(Ca) in the concentration-dependent manners. The IC50 values of berberine-induced inhibition of IK(V) and IK(Ca) were approximately 15 microM and 50 microM, respectively. In inside-out configurations, berberine inside the pipette suppressed the activity of K(Ca) channels without changing the single channel conductance. Berberine also inhibited the proliferation of this cell line and the IC50 value of berberine-induced inhibition of cell proliferation was 5 microM. Thus, the cytotoxic effect of berberine in cancer cells may be partially explained by its direct blockade of these K+ channels.

Antineoplastic Agents↗