Rat Prl and TSH secretion are regulated differently by K(+)-channel blockers

1994 ◽  
Vol 266 (1) ◽  
pp. E39-E43 ◽  
Author(s):  
X. Wang ◽  
T. Inukai ◽  
M. A. Greer ◽  
S. E. Greer
Keyword(s):  
Channel Blocker ◽  
Cell Types ◽  
Inhibitory Effect ◽  
Thyroid Stimulating Hormone ◽  
K Channel ◽  
Channel Blockers ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
K Channels ◽  
Tsh Secretion

All four different K(+)-channel blockers [tetraethylammonium (TEA), a nonselective K(+)-channel blocker; tolbutamide, an ATP-sensitive K(+)-channel blocker; quinine and 4-aminopyridine, both primarily voltage-dependent K(+)-channel blockers] stimulated prolactin (Prl) secretion by acutely dispersed anterior pituitary cells but had no effect on thyroid-stimulating hormone (TSH) secretion. TEA stimulated Prl secretion in a dose-dependent manner between 1 microM and 20 mM, but even as high as 20 mM, TEA did not induce TSH secretion. Valinomycin (2 microM), a K+ ionophore, inhibited both basal and TEA-induced Prl secretion. TEA-stimulated Prl secretion was abolished by using a Ca(2+)-depleted medium or adding 10 microM dopamine. TEA did not reverse the inhibitory effect of dopamine on thyrotropin-releasing hormone-induced Prl secretion. Our data indicate that K+ channels may play a role in the secretion of adenohypophysial hormones that is idiosyncratic for each hormone. Differences in the role of K+ channels may reflect differences between the various pituitary cell types in plasma membrane ion channel composition, membrane potential, or the mechanism of exocytosis.

scholarly journals Arachidonic acid inhibits basolateral K channels in the cortical collecting duct via cytochrome P-450 epoxygenase-dependent metabolic pathways

2008 ◽  
Vol 294 (6) ◽  
pp. F1441-F1447 ◽  
Author(s):  
ZhiJian Wang ◽  
Yuan Wei ◽  
John R. Falck ◽  
Krishnam Raju Atcha ◽  
Wen-Hui Wang
Keyword(s):  
Arachidonic Acid ◽  
Collecting Duct ◽  
Rat Kidney ◽  
Inhibitory Effect ◽  
K Channel ◽  
Dependent Manner ◽  
Cortical Collecting Duct ◽  
Patch Clamp Technique ◽  
K Channels ◽  
Cytochrome P 450

We used the patch-clamp technique to study the effect of arachidonic acid (AA) on basolateral 18-pS K channels in the principal cell of the cortical collecting duct (CCD) of the rat kidney. Application of AA inhibited the 18-pS K channels in a dose-dependent manner and 10 μM AA caused a maximal inhibition. The effect of AA on the 18-pS K channel was specific because application of 11,14,17-eicosatrienoic acid had no effect on channel activity. Also, the inhibitory effect of AA on the 18-pS K channels was abolished by blocking cytochrome P-450 (CYP) epoxygenase with N-methylsulfonyl-6-(propargyloxyphenyl)hexanamide (MS-PPOH) but was not affected by inhibiting CYP ω-hydroxylase or cyclooxygenase. The notion that the inhibitory effect of AA was mediated by CYP epoxygenase-dependent metabolites was further supported by the observation that application of 100 nM 11,12-epoxyeicosatrienoic acid (EET) mimicked the effect of AA and inhibited the basolateral 18-pS K channels. In contrast, addition of either 5,6-, 8,9-, or 14,15-EET failed to inhibit the 18-pS K channels. Moreover, application of 11,12-EET was still able to inhibit the 18-pS K channels in the presence of MS-PPOH. This suggests that 11,12-EET is a mediator for the AA-induced inhibition of the 18-pS K channels. We conclude that AA inhibits basolateral 18-pS K channels by a CYP epoxygenase-dependent pathway and that 11,12-EET is a mediator for the effect of AA on basolateral K channels in the CCD.

Mechanisms of neurotensin-induced inhibition in rat ileal smooth muscle

1992 ◽  
Vol 263 (5) ◽  
pp. G767-G774 ◽  
Author(s):  
H. D. Allescher ◽  
H. Fick ◽  
V. Schusdziarra ◽  
M. Classen
Keyword(s):  
Smooth Muscle ◽  
Channel Blocker ◽  
Inhibitory Concentration ◽  
Longitudinal Muscle ◽  
Inhibitory Effect ◽  
Repetitive Stimulation ◽  
K Channel ◽  
Channel Blockers ◽  
Organ Bath ◽  
Dependent Inhibition

The aim of the present study was to determine the mechanisms of neurotensin-induced inhibition in ileal smooth muscle. Isolated rat ileal smooth muscle strips were stimulated in an organ bath using carbachol (CCH) or by KCl depolarization. Neurotensin produced a concentration-dependent inhibition of muscle contraction [mean inhibitory concentration (IC50): 2.8 x 10(-9) M], which was not blocked by phentolamine (10(-6) M), hexamethonium (10(-4) M), indomethacin (10(-6) M), nordihydroguaretic acid (10(-6) M), or tetrodotoxin (10(-6) M). The inhibitory effect of neurotensin during CCH stimulation was blocked concentration dependently in the presence of the K(+)-channel blocker apamin. By contrast, other K(+)-channel blockers such as 9-aminoacridine (10(-6) M to 3 x 10(-5) M), 4-aminopyridine (10(-4) M to 5 x 10(-3) M), tetraethylammonium (10(-4) M to 10(-1) M), or glibenclamide (10(-5) M) were ineffective. The presence of the Ca(2+)-channel antagonist nitrendipine (IC50: 2.4 x 10(-9) M) or verapamil (IC50: 1.1 x 10(-7) M) also blocked the neurotensin inhibitory effect. Ileal contraction, induced by the Ca(2+)-channel activator BAY K 8644 (10(-7) M), was completely inhibited by neurotensin. After depletion of internal Ca2+ stores by repetitive stimulation with CCH and caffeine in Ca(2+)-free buffer, reintroduction of external Ca2+ restored neurotensin inhibition of the contraction induced by CCH. These results demonstrate that the inhibitory effect of neurotensin in rat ileum longitudinal muscle is apamin sensitive and cannot be observed in the presence of the Ca(2+)-channel blockers nitrendipine or verapamil.(ABSTRACT TRUNCATED AT 250 WORDS)

TEA inhibits ACh-induced EDRF release: endothelial Ca(2+)-dependent K+ channels contribute to vascular tone

1994 ◽  
Vol 267 (3) ◽  
pp. H1135-H1141 ◽  
Author(s):  
E. Demirel ◽  
J. Rusko ◽  
R. E. Laskey ◽  
D. J. Adams ◽  
C. van Breemen
Keyword(s):  
Endothelial Cells ◽  
Patch Clamp ◽  
Outward Current ◽  
Rabbit Aorta ◽  
K Channel ◽  
Channel Blockers ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
K Channels ◽  
Donor Segment

The effects of K(+)-channel blockers on the acetylcholine (ACh)-induced relaxation of vascular smooth muscle, intracellular free Ca2+ concentration ([Ca2+]i) elevation, and ACh-evoked outward K+ current of endothelial cells of rabbit aorta were studied using bioassay, spectrofluorimetry, and patch-clamp techniques, respectively. In bioassay experiments, ACh caused relaxation of endothelium-denuded aortic rings in a concentration-dependent manner when perfused through an endothelium-intact donor segment of aorta but not when perfused directly onto the recipient aortic ring. ACh-induced relaxation was inhibited by perfusion of tetraethylammonium ions (TEA; 5 mM) through the donor but not by perfusion directly onto the recipient segment. Glibenclamide had no effect on ACh-induced relaxation of the bioassay ring in either situation. ACh increased [Ca2+]i at the endothelial surface of aortic strips but not at the adventitial surface. TEA inhibited ACh-induced [Ca2+]i elevation, whereas glibenclamide had no effect. In patch-clamp experiments with freshly isolated endothelial cells, ACh evoked a biphasic outward current which was completely abolished by TEA (3 mM). It is concluded that Ca(2+)-dependent K+ channels are important for increasing [Ca2+]i during agonist stimulation and consequently for the synthesis/release of endothelium-derived relaxing factors (EDRFs). Furthermore, endothelial ATP-sensitive K+ channels do not contribute to ACh-induced relaxation or evoke an increase in endothelial [Ca2+]i of rabbit thoracic aorta.

scholarly journals Voltage-gated potassium channels are required for human T lymphocyte activation.

1984 ◽  
Vol 160 (2) ◽  
pp. 369-385 ◽  
Author(s):  
K G Chandy ◽  
T E DeCoursey ◽  
M D Cahalan ◽  
C McLaughlin ◽  
S Gupta
Keyword(s):  
Protein Synthesis ◽  
T Lymphocytes ◽  
T Lymphocyte ◽  
Lymphocyte Activation ◽  
K Channel ◽  
Channel Blockers ◽  
Dependent Manner ◽  
Two Dimensional Gel Electrophoresis ◽  
K Channels ◽  
T Lymphocyte Activation

The calcium channel blockers, verapamil and diltiazem, inhibit phytohemagglutinin (PHA)-induced mitogenesis at concentrations that block the T lymphocyte K channel currents. K channel blockers also inhibit the allogeneic mixed lymphocyte response in a dose-dependent manner with the same potency sequence as for block of K currents. K channel blockers inhibit PHA-stimulated mitogenesis only if added during the first 20-30 h after PHA addition, but not later, indicating a requirement for functional K channels during this period. We investigated the effect of K channel blockers on various aspects of protein synthesis for two reasons: first, protein synthesis appears to be necessary for the events leading to DNA synthesis, and second, the increase in the protein synthetic rate commences during the first 24-48 h after PHA addition. PHA-induced total protein synthesis was reduced to the level in unstimulated T lymphocytes by K channel blockers in a dose-dependent manner with the same potency sequence as for the block of K currents and inhibition of [3H]thymidine incorporation. Two-dimensional gel electrophoresis demonstrated that although the synthesis of the majority of proteins was reduced by K channel blockers to the level in unstimulated T cells, some proteins continued to be synthesized at an enhanced rate compared with resting cells. Two proteins, S and T, detected by two-dimensional gel electrophoresis in unstimulated T lymphocytes, appeared to be reduced in intensity in gels of PHA-treated T lymphocytes, in contrast to the increased synthesis of the remaining proteins. 4-Aminopyridine (4-AP), at concentrations that inhibit protein synthesis, prevented the apparent PHA-induced reduction of proteins S and T. These proteins may play a role in maintaining the T lymphocyte in a resting state and may be related to the translation inhibitory factors reported to be present at a higher specific activity in quiescent T lymphocytes than in PHA-activated T cells. The expression of the IL-2 receptor (Tac) during T lymphocyte activation was not altered by K channel blockers, whereas the production of interleukin 2 (IL-2) was reduced to the level in unstimulated T lymphocytes. Exogenous IL-2 partially relieved the inhibition of mitogenesis by low, but not by high, concentrations of 4-AP. These experiments clarify the role of K channels in T lymphocyte activation and suggest that functional K channels are required either for protein synthesis or for events leading to protein synthesis.

Somatostatin blocks the potentiation of TRH-induced TSH secretion from perifused pituitary fragments and the change in intracellular calcium concentrations from dispersed pituitary cells elicited by prepro-TRH (PS4) or by tri-iodothyronine

1997 ◽  
Vol 19 (1) ◽  
pp. 87-97 ◽  
Author(s):  
J-P Roussel ◽  
E Grazzini ◽  
H Astier
Keyword(s):  
Primary Cultures ◽  
Inhibitory Effect ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
Physiological Concentration ◽  
Rat Pituitary ◽  
Tsh Secretion ◽  
Intracellular Ca ◽  
Dose Dependent

ABSTRACT TRH and somatostatin (SRIH) are well known to stimulate and to inhibit TSH secretion respectively. However, the mechanisms underlying the effect of SRIH on thyrotrophs are still not understood. We have previously shown in vitro that the TSH response to TRH is potentiated in a Ca2+-dependent fashion through the activation of dihydropyridine (DHP)-sensitive Ca2+ channels by the prepro-TRH (160-169) cryptic peptide (PS4) and tri-iodo-l-thyronine (T3), when the hormone was added shortly before a TRH pulse in order to avoid its genomic effect. Using perifused rat pituitary fragments, the present study has shown that SRIH inhibits, in a dose-dependent manner, the TSH response to physiological concentration of TRH (10 nm) and reverses the Ca2+-dependent potentiation of that response induced either by PS4 or by T3. We have also demonstrated that the inhibition by SRIH of the T3 potentiation of TRH-induced TSH secretion is pertussis toxinsensitive. Our data suggest that SRIH inhibits the PS4 and T3 potentiation of TRH-induced TSH secretion through the inactivation of DHP-sensitive Ca2+ channels. Using primary cultures of rat anterior pituitary cells and videomicroscopy, we have already demonstrated that TRH, as well as PS4 and T3, are able to increase intracellular Ca2+ concentration ([Ca2+]i) rapidly, in 15 s. Our study has shown that SRIH is able to abolish the acute rise in [Ca2+]i induced either by PS4 or by T3. Since [Ca2+]i responses to PS4 and T3 are also abolished by the DHP nifedipine, our results suggest that [Ca2+]i changes in PS4- or T3-sensitive pituitary cells depend directly or indirectly on the activation of DHP-sensitive Ca2+ channels and that the inhibitory effect of SRIH may be mediated by inactivation of this type of channel.

Contribution of potassium channels to active hyperemia of the canine diaphragm

1994 ◽  
Vol 76 (3) ◽  
pp. 1098-1105 ◽  
Author(s):  
G. Vanelli ◽  
H. Y. Chang ◽  
A. G. Gatensby ◽  
S. N. Hussain
Keyword(s):  
Blood Flow ◽  
Nerve Stimulation ◽  
Phrenic Nerve ◽  
Channel Blocker ◽  
K Channel ◽  
Channel Blockers ◽  
O2 Uptake ◽  
Phrenic Nerve Stimulation ◽  
K Channels ◽  
Small Conductance

Glibenclamide, iberiotoxin, and apamin (blockers of ATP-sensitive, large-conductance, and small-conductance Ca(2+)-activated K+ channels, respectively) were infused into the diaphragmatic vasculature of anesthetized indomethacin-treated dogs to assess the contribution of K+ channels to active hyperemia. Diaphragmatic blood flow (Qphr) and O2 uptake (VO2di) were measured at rest and during 2 min of continuous left phrenic nerve stimulation at 0.5, 1, 2, and 4 Hz. These measurements were repeated before (control) and after the infusion of a selective K+ channel blocker in three groups of animals. Glibenclamide at 10(-5) M significantly attenuated Qphr at rest and in response to all stimulation frequencies. Whereas resting VO2di remained unchanged, glibenclamide infusion significantly reduced VO2di in response to all stimulation frequencies. The slope of the linear relationship between Qphr and VO2di, however, was not affected by glibenclamide. By comparison, infusion of iberiotoxin (10(-7) M) in a second group reduced Qphr at rest and in response to 0.5- and 1-Hz stimulation, whereas Qphr measured in response to 2- and 4-Hz stimulation remained similar to control values. Apamin (10(-6) M) infusion in a third group reduced only resting Qphr with no effect on active hyperemia during phrenic nerve stimulation. Neither iberiotoxin nor apamin influenced resting or stimulated VO2di. In all groups diaphragmatic tension measured after the infusion of K+ channel blockers remained similar to control values. These results indicate that K+ channels, especially those sensitive to glibenclamide, modulate the increase in Qphr and VO2di in response to moderate augmentation of metabolic demands.

Distinct pathways to refill ACh-sensitive internal Ca2+ stores in canine airway smooth muscle

1993 ◽  
Vol 265 (1) ◽  
pp. C28-C35 ◽  
Author(s):  
J. P. Bourreau ◽  
C. Y. Kwan ◽  
E. E. Daniel
Keyword(s):  
Smooth Muscle ◽  
Channel Blocker ◽  
Cyclopiazonic Acid ◽  
Inhibitory Effect ◽  
Tonic Contraction ◽  
The Other ◽  
K Channel ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
K Channel Opener

The ability of extracellular Ca2+ to refill internal Ca2+ stores of canine tracheal smooth muscle after a prior depletion by acetylcholine (ACh) was assessed using a novel sarcoplasmic reticulum (SR) Ca2+ pump inhibitor, cyclopiazonic acid (CPA). The transient contraction induced by ACh in a medium free of Ca2+ was used as an index for the content of agonist-sensitive intracellular Ca2+ stores. CPA inhibited in a concentration-dependent manner the refilling of the stores occurring during high KCl stimulation, and this inhibitory effect was independent of the external Ca2+ concentration. On the other hand, CPA was less effective in inhibiting the refilling occurring during prolonged ACh stimulation, especially when external Ca2+ concentration was raised. At 5.0 mM external Ca2+ or when 0.1 microM BAY 8644 was present in the medium, CPA was ineffective in inhibiting the refilling occurring during prolonged ACh stimulation. The maximum ACh-induced contraction in Ca(2+)-containing medium was independent of the extent of internal store Ca2+ load in the absence of L-type Ca2+ channel blocker but was highly dependent on the extent of internal Ca2+ load in the presence of the Ca2+ channel blocker. Hyperpolarization of the plasma membrane with the K+ channel opener cromakalim reduced the amplitude of ACh tonic contraction. Subsequent addition of nifedipine further reduced ACh tonic contraction. It is concluded that two different pathways for external Ca2+ are used to refill ACh-sensitive internal stores. One involves active Ca2+ uptake via a CPA-sensitive Ca2+ pump, and the other involves a CPA-insensitive pathway whose nature remains to be determined.

Arabidopsis AtCNGC10 rescues potassium channel mutants of E. coli, yeast and Arabidopsis and is regulated by calcium/calmodulin and cyclic GMP in E. coli

2005 ◽  
Vol 32 (7) ◽  
pp. 643 ◽  
Author(s):  
Xinli Li ◽  
Tamás Borsics ◽  
H. Michael Harrington ◽  
David A. Christopher
Keyword(s):  
Channel Blocker ◽  
K Channel ◽  
Structure Characteristic ◽  
Dependent Manner ◽  
Wild Type ◽  
Yeast Saccharomyces Cerevisiae ◽  
E Coli ◽  
Diverse Species ◽  
The Family ◽  
Low K

We have isolated and characterised AtCNGC10, one of the 20 members of the family of cyclic nucleotide (CN)-gated and calmodulin (CaM)-regulated channels (CNGCs) from Arabidopsis thaliana (L.) Heynh. AtCNGC10 bound CaM in a C-terminal subregion that contains a basic amphiphillic structure characteristic of CaM-binding proteins and that also overlaps with the predicted CN-binding domain. AtCNGC10 is insensitive to the broad-range K+ channel blocker, tetraethylammonium, and lacks a typical K+-signature motif. However, AtCNGC10 complemented K+ channel uptake mutants of Escherichia coli (LB650), yeast (Saccharomyces cerevisiae CY162) and Arabidopsis (akt1-1). Sense 35S-AtCNGC10 transformed into the Arabidopsis akt1-1 mutant, grew 1.7-fold better on K+-limited medium relative to the vector control. Coexpression of CaM and AtCNGC10 in E. coli showed that Ca2+ / CaM inhibited cell growth by 40%, while cGMP reversed the inhibition by Ca2+ / CaM, in a AtCNGC10-dependent manner. AtCNGC10 did not confer tolerance to Cs+ in E. coli, however, it confers tolerance to toxic levels of Na+ and Cs+ in the yeast K+ uptake mutant grown on low K+ medium. Antisense AtCNGC10 plants had 50% less potassium than wild type Columbia. Taken together, the studies from three evolutionarily diverse species demonstrated a role for the CaM-binding channel, AtCNGC10, in mediating the uptake of K+ in plants.

Enhanced role of K+ channels in relaxations of hypercholesterolemic rabbit carotid artery to NO

1995 ◽  
Vol 269 (3) ◽  
pp. H805-H811 ◽  
Author(s):  
S. Najibi ◽  
R. A. Cohen
Keyword(s):  
Carotid Artery ◽  
Sodium Nitroprusside ◽  
Channel Blocker ◽  
Isometric Tension ◽  
K Channel ◽  
K Channels ◽  
Rabbit Carotid Artery ◽  
Cyclic Monophosphate ◽  
Endothelium Dependent Relaxation

Endothelium-dependent relaxations to acetylcholine remain normal in the carotid artery of hypercholesterolemic rabbits, but unlike endothelium-dependent relaxations of normal rabbits, they are inhibited by charybdotoxin, a specific blocker of Ca(2+)-dependent K+ channels. Because nitric oxide (NO) is the mediator of endothelium-dependent relaxation and can activate Ca(2+)-dependent K+ channels directly or via guanosine 3',5'-cyclic monophosphate, the present study investigated the role of Ca(2+)-dependent K+ channels in relaxations caused by NO, sodium nitroprusside, and 8-bromoguanosine 3',5'-cyclic monophosphate (8-Brc-GMP) in hypercholesterolemic rabbit carotid artery. Isometric tension was measured in rabbit carotid artery denuded of endothelium from normal and hypercholesterolemic rabbits which were fed 0.5% cholesterol for 12 wk. Under control conditions, relaxations to all agents were similar in normal and hypercholesterolemic rabbit arteries. Charybdotoxin had no significant effect on relaxations of normal arteries to NO, sodium nitroprusside, or 8-BrcGMP, but the Ca(2+)-dependent K+ channel blocker significantly inhibited the relaxations caused by each of these agents in the arteries from hypercholesterolemic rabbits. By contrast, relaxations to the calcium channel blocker nifedipine were potentiated to a similar extent by charybdotoxin in both groups. In addition, arteries from hypercholesterolemic rabbits relaxed less than normal to sodium nitroprusside when contracted with depolarizing potassium solution. These results indicate that although nitrovasodilator relaxations are normal in the hypercholesterolemic rabbit carotid artery, they are mediated differently, and to a greater extent, by Ca(2+)-dependent K+ channels. These data also suggest that K+ channel-independent mechanism(s) are impaired in hypercholesterolemia.

scholarly journals Tenovin-6 impairs autophagy by inhibiting autophagic flux

2017 ◽  
Vol 8 (2) ◽  
pp. e2608-e2608 ◽  
Author(s):  
Hongfeng Yuan ◽  
Brandon Tan ◽  
Shou-Jiang Gao
Keyword(s):  
Cell Types ◽  
Inhibitory Effect ◽  
Lymphocytic Leukemia ◽  
Autophagic Flux ◽  
Dependent Manner ◽  
Autophagy Pathway ◽  
Sarcoma Cells ◽  
Regulatory Functions

Abstract Tenovin-6 has attracted significant interest because it activates p53 and inhibits sirtuins. It has anti-neoplastic effects on multiple hematopoietic malignancies and solid tumors in both in vitro and in vivo studies. Tenovin-6 was recently shown to impair the autophagy pathway in chronic lymphocytic leukemia cells and pediatric soft tissue sarcoma cells. However, whether tenovin-6 has a general inhibitory effect on autophagy and whether there is any involvement with SIRT1 and p53, both of which are regulators of the autophagy pathway, remain unclear. In this study, we have demonstrated that tenovin-6 increases microtubule-associated protein 1 light chain 3 (LC3-II) level in diverse cell types in a time- and dose-dependent manner. Mechanistically, the increase of LC3-II by tenovin-6 is caused by inhibition of the classical autophagy pathway via impairing lysosomal function without affecting the fusion between autophagosomes and lysosomes. Furthermore, we have revealed that tenovin-6 activation of p53 is cell type dependent, and tenovin-6 inhibition of autophagy is not dependent on its regulatory functions on p53 and SIRT1. Our results have shown that tenovin-6 is a potent autophagy inhibitor, and raised the precaution in interpreting results where tenovin-6 is used as an inhibitor of SIRT1.

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