scholarly journals Mechanisms of Two Modulatory Actions of the Channel-binding Protein Slob on the Drosophila Slowpoke Calcium-dependent Potassium Channel

2006 ◽  
Vol 128 (5) ◽  
pp. 583-591 ◽  
Author(s):  
Haoyu Zeng ◽  
Thomas M. Weiger ◽  
Hong Fei ◽  
Irwin B. Levitan
Keyword(s):  
Potassium Channel ◽  
Voltage Dependence ◽  
Calcium Sensitivity ◽  
Dependent Manner ◽  
Voltage Shift ◽  
Calcium Dependent ◽  
Channel Inactivation ◽  
And Shifts ◽  
Dose Dependent ◽  
Independent Mutation

Slob57 is an ion channel auxiliary protein that binds to and modulates the Drosophila Slowpoke calcium-dependent potassium channel (dSlo). We reported recently that residues 1–39 of Slob57 comprise the key domain that both causes dSlo inactivation and shifts its voltage dependence of activation to more depolarized voltages. In the present study we show that removal of residues 2–6 from Slob57 abolishes the inactivation, but the ability of Slob57 to rightward shift the voltage dependence of activation of dSlo remains. A synthetic peptide corresponding in sequence to residues 1–6 of Slob57 blocks dSlo in a voltage- and dose-dependent manner. Two Phe residues and at least one Lys residue in this peptide are required for the blocking action. These data indicate that the amino terminus of Slob57 directly blocks dSlo, thereby leading to channel inactivation. Further truncation to residue Arg16 eliminates the modulation of voltage dependence of activation. Thus these two modulatory actions of Slob57 are independent. Mutation within the calcium bowl of dSlo greatly reduces its calcium sensitivity (Bian, S., I. Favre, and E. Moczydlowski. 2001. Proc. Natl. Acad. Sci. USA. 98:4776–4781). We found that Slob57 still causes inactivation of this mutant channel, but does not shift its voltage dependence of activation. This result confirms further the independence of the inactivation and the voltage shift produced by Slob57. It also suggests that the voltage shift requires high affinity Ca2+ binding to an intact calcium bowl. Furthermore, Slob57 inhibits the shift in the voltage dependence of activation of dSlo evoked by Ca2+, and this inhibition by Slob57 is greater at higher free Ca2+ concentrations. These results implicate distinct calcium-dependent and -independent mechanisms in the modulation of dSlo by Slob.

Isoflurane-induced Dilation of Porcine Coronary Microvessels Is Endothelium Dependent and Inhibited by Glibenclamide

2002 ◽  
Vol 96 (6) ◽  
pp. 1465-1471 ◽  
Author(s):  
A. Kurt Gamperl ◽  
Travis W. Hein ◽  
Lih Kuo ◽  
Brian A. Cason
Keyword(s):  
Potassium Channel ◽  
Sodium Nitroprusside ◽  
Adenosine Triphosphate ◽  
Channel Blocker ◽  
Minimum Alveolar Concentration ◽  
Channel Blockers ◽  
Dependent Manner ◽  
Presence And Absence ◽  
Dose Dependent

Background Isoflurane has been reported to cause dose-dependent constriction in isolated coronary microvessels. However, these results are inconsistent with data from in situ and in vivo heart preparations which show that isoflurane dilates the coronary vasculature. To clarify the direct effects of isoflurane on coronary tone, we measured the response of isolated porcine resistance arterioles (ID, 75 +/- 4.0 microm; range, 41-108 microm) to isoflurane in the presence and absence of adenosine triphosphate-sensitive and Ca2+-activated potassium channel blockers and also after endothelial removal. Methods Subepicardial arterioles were isolated, cannulated, and pressurized to 45 mmHg without flow in a 37 degrees C vessel chamber filled with MOPS buffer (pH = 7.4). After all vessels developed spontaneous (intrinsic) tone, dose-dependent (0.17-0.84 mm; approximately 0.5-2.5 minimum alveolar concentration) isoflurane-mediated effects on vessel ID were studied in the presence and absence of extraluminal glibenclamide (1 microm; an adenosine triphosphate-sensitive channel blocker) or iberiotoxin (100 nm; a Ca2+-activated potassium channel blocker) or before and after endothelial denudation using the nonionic detergent CHAPS (0.4%). Vessel ID was measured using an inverted microscope and videomicrometer, and vasomotor responses were analyzed by normalizing changes in arteriole ID to the dilation observed after exposure to 10-4 m sodium nitroprusside, which causes maximal dilation. Results Isoflurane caused dose-dependent dilation of all coronary arterioles. This vasodilation was 6.0 +/- 0.7 microm at an isoflurane concentration of 0.16 mm (approximately 0.5 minimum alveolar concentration) and 25.3 +/- 2.1 microm at 0.75 mm (approximately 2.5 minimum alveolar concentration). These values represent 18.1 +/- 1.7% and 74.1 +/- 3.3%, respectively, of that observed with 10-4 sodium nitroprusside (34 +/- 3 microm). Glibenclamide, but not iberiotoxin, exposure affected arteriolar dilation in response to isoflurane. Glibenclamide caused a downward displacement of the isoflurane dose-response curve, reducing isoflurane-mediated dilation by an average of 36%. Denuded arterioles showed a marked (approximately 70%) reduction in their ability to dilate in response to isoflurane. Conclusions The authors conclude that isoflurane dilates coronary resistance arterioles in a dose-dependent manner, and that this dilation is partially mediated by adenosine triphosphate-sensitive channels and is highly dependent on the presence of a functioning endothelium.

scholarly journals N-bromoacetamide removes a calcium-dependent component of channel opening from calcium-activated potassium channels in rat skeletal muscle.

1985 ◽  
Vol 86 (5) ◽  
pp. 601-611 ◽  
Author(s):  
B S Pallotta
Keyword(s):  
Skeletal Muscle ◽  
Potassium Channels ◽  
Voltage Dependence ◽  
Calcium Sensitivity ◽  
Rat Skeletal Muscle ◽  
Open Probability ◽  
Calcium Dependent ◽  
Channel Opening ◽  
Dependent Component ◽  
Calcium Activated Potassium Channels

Calcium-activated potassium channels from cultured rat skeletal muscle were treated with the protein-modifying reagent N-bromoacetamide (NBA) (0.3-1 mM) and studied in excised patches using patch-clamp techniques. After NBA treatment, channels opened only occasionally, and, in contrast to untreated channels, the open probability was no longer sensitive to intracellular surface calcium ions (1 nM to 100 microM). Channel activity did, however, exhibit a voltage dependence similar in direction and magnitude to that shown before NBA treatment (increasing e-fold with 19 mV depolarization). Distributions of open channel lifetimes revealed that NBA treatment virtually abolished openings of long duration, which suggests that this class of openings requires calcium sensitivity. These effects were not reversed by subsequent washing. Quantitatively similar open probability, voltage dependence, and open-interval distributions were observed in untreated channels in calcium-free medium. These results suggest that NBA removed a calcium-dependent component of channel opening, and that normal channels are able to open in the absence of significant intracellular calcium concentrations.

scholarly journals Microbial Quorum-Sensing Molecules Induce Acrosome Loss and Cell Death in Human Spermatozoa

2009 ◽  
Vol 77 (11) ◽  
pp. 4990-4997 ◽  
Author(s):  
Claudia Rennemeier ◽  
Torsten Frambach ◽  
Florian Hennicke ◽  
Johannes Dietl ◽  
Peter Staib
Keyword(s):  
Quorum Sensing ◽  
Communication Systems ◽  
Homoserine Lactone ◽  
Human Spermatozoa ◽  
Dependent Manner ◽  
Pathogenic Yeast ◽  
Calcium Dependent ◽  
Opportunistic Pathogenic ◽  
Apoptosis And Necrosis ◽  
Dose Dependent

ABSTRACT Infertility in men and women is frequently associated with genital contamination by various commensal or uropathogenic microbes. Since many microorganisms are known to release quorum-sensing signals in substantial amounts, we raised the question whether such molecules can directly affect human spermatozoa. Here we show that farnesol and 3-oxododecanoyl-l-homoserine lactone, employed by the opportunistic pathogenic yeast Candida albicans and the gram-negative bacterium Pseudomonas aeruginosa, respectively, induce multiple damage in spermatozoa. A reduction in the motility of spermatozoa coincided in a dose-dependent manner with apoptosis and necrosis at concentrations which were nondeleterious for dendritic cell-like immune cells. Moreover, sublethal doses of both signaling molecules induced premature loss of the acrosome, a cap-like structure of the sperm head which is essential for fertilization. Addressing their mechanism of action, we found that the bacterial molecule, but not the fungal molecule, actively induced the acrosome reaction via a calcium-dependent mechanism. This work uncovers a new facet in the interaction of microorganisms with human gametes and suggests a putative link between microbial communication systems and host infertility.

scholarly journals Inhibition of sodium currents by local anesthetics in chloramine-T-treated squid axons. The role of channel activation.

1987 ◽  
Vol 89 (4) ◽  
pp. 645-667 ◽  
Author(s):  
G K Wang ◽  
M S Brodwick ◽  
D C Eaton ◽  
G R Strichartz
Keyword(s):  
Local Anesthetics ◽  
Voltage Dependence ◽  
Time Dependent ◽  
Na Channel ◽  
Dependent Manner ◽  
Channel Activation ◽  
Channel Inactivation ◽  
Phasic Block ◽  
Na Currents ◽  
Chloramine T

In order to test the requirement of Na channel inactivation for the action of local anesthetics, we investigated the inhibitory effects of quaternary and tertiary amine anesthetics on normally inactivating and noninactivating Na currents in squid axons under voltage clamp. Either the enzymatic mixture pronase, or chloramine-T (CT), a noncleaving, oxidizing reagent, was used to abolish Na channel inactivation. We found that both the local anesthetics QX-314 and etidocaine, when perfused internally at 1 mM, elicited a "tonic" (resting) block of Na currents, a "time-dependent" block that increased during single depolarizations, and a "use-dependent" (phasic) block that accumulated as a result of repetitive depolarizations. All three effects occurred in both control and CT-treated axons. As in previous reports, little time-dependent or phasic block by QX-314 appeared in pronase-treated axons, although tonic block remained. Time-dependent block was greatest and fastest at large depolarizations (Em greater than +60 mV) for both the control and CT-treated axons. The recovery kinetics from phasic block were the same in control and CT-modified axons. The voltage dependence of the steady state phasic block in CT-treated axons differed from that in the controls; an 8-10% reduction of the maximum phasic block and a steepening and shift of the voltage dependence in the hyperpolarizing direction resulted from CT treatment. The results show that these anesthetics can bind rapidly to open Na channels in a voltage-dependent manner, with no requirement for fast inactivation. We propose that the rapid phasic blocking reactions in nerve are consequences primarily of channel activation, mediated by binding of anesthetics to open channels, and that the voltage dependence of phasic block arises directly from that of channel activation.

scholarly journals Insect cardioactive peptides. II. Neurohormonal control of heart activity by two cardioacceleratory peptides in the tobacco hawkmoth, Manduca sexta

1985 ◽  
Vol 114 (1) ◽  
pp. 381-395 ◽  
Author(s):  
N. J. Tublitz ◽  
J. W. Truman
Keyword(s):  
Heart Rate ◽  
Manduca Sexta ◽  
Gel Filtration ◽  
Dependent Manner ◽  
Heart Activity ◽  
High Potassium ◽  
Calcium Dependent ◽  
Dose Dependent Increase ◽  
Dose Dependent

The physiological characteristics of two cardioacceleratory peptides (CAPs) were analysed in the tobacco hawkmoth, Manduca sexta, to determine if either CAP functioned as a cardioregulatory neurohormone. In vivo heart recordings from pharate and newly emerged adults revealed a dramatic increase in heart rate associated with wing-spreading behaviour. Bioassay of whole blood taken from wing-spreading (WS) animals indicated the presence of a stage-specific, blood-borne cardioacceleratory factor(s). Gel filtration of WS blood identified two cardioacceleratory factors which co-eluted with the two CAPs. A depletion of the ventral nerve cord levels of both CAPs was observed during WS behaviour. Measurements of blood CAP levels showed that the peak CAP titres were coincident with the initiation of WS behaviour. Experimental manipulations that delayed the onset of WS behaviour also prevented CAP release. High potassium incubation evoked the release of both CAPs in a calcium-dependent manner. In vivo injections of CAP1 or CAP2 caused a dose-dependent increase in heart rate. These results confirm the hypothesis that both CAPs function as cardioregulatory neurohormones during wing-spreading behaviour in Manduca sexta.

scholarly journals Newly Discovered Action of HpTx3 from Venom of Heteropoda venatoria on Nav1.7 and Its Pharmacological Implications in Analgesia

Toxins ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 680
Author(s):  
Xinzhou Wu ◽  
Zhouquan Wang ◽  
Yu Chen ◽  
Dehong Xu ◽  
Peng Zhang ◽  
...  
Keyword(s):  
Voltage Dependence ◽  
Molecular Probe ◽  
Dependent Manner ◽  
Hot Plate ◽  
Current Voltage ◽  
Pain Models ◽  
Steady State Inactivation ◽  
Relationship Of ◽  
Dose Dependent ◽  
Pore Blocker

It has been reported that Heteropodatoxin3 (HpTx3), a peptidic neurotoxin purified from the venom of the spider species Heteropoda venatoria, could inhibit Kv4.2 channels. Our present study newly found that HpTx3 also has potent and selective inhibitory action on Nav1.7, with an IC50 of 135.61 ± 12.98 nM. Without effect on the current–voltage (I-V) relationship of Nav1.7, HpTx3 made minor alternation in the voltage-dependence of activation and steady-state inactivation of Nav1.7 (4.15 mV and 7.29 mV, respectively) by interacting with the extracellular S3–S4 loop (S3b–S4 sequence) in domain II and the domain IV of the Nav channel subtype, showing the characteristics of both pore blocker and gate modifier toxin. During the interaction of HpTx3 with the S3b–S4 sequence of Nav1.7, the amino acid residue D in the sequence played a key role. When administered intraperitoneally or intramuscularly, HpTx3 displayed potent analgesic activity in a dose-dependent manner in different mouse pain models induced by formalin, acetic acid, complete Freund’s adjuvant, hot plate, or spared nerve injury, demonstrating that acute, inflammatory, and neuropathic pains were all effectively inhibited by the toxin. In most cases HpTx3 at doses of ≥ 1mg/kg could produce the analgesic effect comparable to that of 1 mg/kg morphine. These results suggest that HpTx3 not only can be used as a molecular probe to investigate ion channel function and pain mechanism, but also has potential in the development of the drugs that treat the Nav1.7 channel-related pain.

scholarly journals Enhancement of desensitization of quisqualate-type glutamate receptor by the dissociative anaesthetic ketamine

1989 ◽  
Vol 141 (1) ◽  
pp. 73-86
Author(s):  
M. L. Ashford ◽  
P. Boden ◽  
R. L. Ramsey ◽  
P. N. Usherwood
Keyword(s):  
Glutamate Receptor ◽  
Dose Response ◽  
Concanavalin A ◽  
Rise Time ◽  
Voltage Dependence ◽  
Dependent Manner ◽  
Response Curves ◽  
Concomitant Reduction ◽  
The Right ◽  
Dose Dependent

Application of ketamine (10(−4)-10(−3)mol l-1) to locust retractor unguis muscle produced a reversible, dose-dependent reduction in neurally evoked twitches, and blocked agonist-induced contractions. With increasing ketamine concentration (5 × 10(−5)-10(−3) mol l-1), the amplitude of glutamate potentials was reduced and dose-response curves for ionophoresis of L-glutamate were shifted to the right, particularly after concanavalin A treatment. Ketamine (10(−4) mol l-1) enhanced the rate of desensitization to consecutive pulses of L-glutamate and this action was eliminated by concanavalin A. The amplitude of the excitatory postsynaptic current (EPSC) was reduced by ketamine (10(−5)-5 × 10(−4) mol l-1) in a dose-dependent manner but without a concomitant reduction in EPSC rise time. The decay phase of the EPSC was usually biphasic in the presence of ketamine (greater than 5 × 10(−5) mol l-1) but did not exhibit any voltage dependence. It is concluded that ketamine enhances desensitization and blocks the channel, particularly the closed form.

Modulation of cardiac Ca2+channels by isoproterenol studied in transgenic mice with altered SR Ca2+ content

1997 ◽  
Vol 273 (5) ◽  
pp. C1666-C1672 ◽  
Author(s):  
Hidenori Sako ◽  
Stuart A. Green ◽  
Evangelia G. Kranias ◽  
Atsuko Yatani
Keyword(s):  
Adrenergic Receptor ◽  
Voltage Dependence ◽  
Ventricular Myocytes ◽  
Dependent Manner ◽  
Wild Type ◽  
Decay Kinetics ◽  
Cardiac Contractile ◽  
Subsequent Application ◽  
Dose Dependent ◽  
Ca2 Channels

Phospholamban (PLB) ablation is associated with enhanced sarcoplasmic reticulum (SR) Ca2+ uptake and attenuation of the cardiac contractile responses to β-adrenergic agonists. In the present study, we compared the effects of isoproterenol (Iso) on the Ca2+ currents ( I Ca) of ventricular myocytes isolated from wild-type (WT) and PLB knockout (PLB-KO) mice. Current density and voltage dependence of I Ca were similar between WT and PLB-KO cells. However, I Ca recorded from PLB-KO myocytes had significantly faster decay kinetics. Iso increased I Ca amplitude in both groups in a dose-dependent manner (50% effective concentration, 57.1 nM). Iso did not alter the rate of I Ca inactivation in WT cells but significantly prolonged the rate of inactivation in PLB-KO cells. When Ba2+ was used as the charge carrier, Iso slowed the decay of the current in both WT and PLB-KO cells. Depletion of SR Ca2+ by ryanodine also slowed the rate of inactivation of I Ca, and subsequent application of Iso further reduced the inactivation rate of both groups. These results suggest that enhanced Ca2+ release from the SR offsets the slowing effects of β-adrenergic receptor stimulation on the rate of inactivation of I Ca.

Oxygen Consumption Mediated by M2 Muscarinic Receptors in Rat Salivary Glands

1987 ◽  
Vol 66 (9) ◽  
pp. 1435-1437 ◽  
Author(s):  
D. Stojić ◽  
M. Terzić
Keyword(s):  
Oxygen Consumption ◽  
Salivary Gland ◽  
Muscarinic Receptors ◽  
Dependent Manner ◽  
Major Salivary Gland ◽  
Sublingual Gland ◽  
Calcium Dependent ◽  
Rat Parotid ◽  
Dose Dependent ◽  
M2 Muscarinic Receptors

Carbachol and oxotremorine stimulated the consumption of oxygen in rat parotid, submandibular, and sublingual gland slices in a dose-dependent manner. Their actions were abolished by atropine and nifedipine but not by trihexyphenidyl. The findings suggest that carbachol and oxotremorine enhanced oxygen consumption in the major salivary gland slices by the activation of the calcium-dependent muscarinic M2 receptors.

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