Effect of Na+ and K+ channel blockade on baseline and anoxia-induced catecholamine release from rat carotid body

1994 ◽  
Vol 77 (6) ◽  
pp. 2606-2611 ◽  
Author(s):  
T. P. Doyle ◽  
D. F. Donnelly
Keyword(s):  
Carotid Body ◽  
K Channel ◽  
Channel Blockers ◽  
Nerve Activity ◽  
Sham Treatment ◽  
K Channels ◽  
Nerve Response ◽  
Carotid Bodies ◽  
Carotid Body Glomus Cells

Ionic membrane currents are hypothesized to play a major role in determining secretion from carotid body glomus cells, and increased secretion likely mediates the increase in nerve activity in response to hypoxia. The hypothesis that Na+ and K+ channels play an important role in determining secretion and nerve activity was tested by measuring single-fiber afferent nerve activity along with an estimate of free tissue catecholamine using Nafion-covered carbon-fiber micro-electrodes placed in rat carotid bodies in vitro. Baseline and anoxia-stimulated (1 min duration; PO2 of approximately 0 Torr at nadir) levels were quantified. Sham treatment had no significant effect. Tetrodotoxin (2 microns) ablated the nerve activity and reduced peak catecholamine (19.5 +/- 3.1 to 14.5 +/- 3.4 microM; P < 0.05). Cesium (10 microns) had no effect on catecholamine but reduced the nerve response (19.8 +/- 2.7 to 7.8 +/- 2.0 Hz; P < 0.05). 4-Aminopyridine (4 mM) significantly reduced the nerve response (17.2 +/- 3.7 to 4.9 +/- 1.9 Hz; P < 0.05) and increased the baseline (0.9 +/- 0.2 to 3.1 +/- 0.8 microM; P < 0.05) and reduced the peak catecholamine (10.0 to 4.3 +/- 0.8 microM; P < 0.05) levels. These results demonstrate that Na+ and K+ channels play an important role in modulating the secretory and nerve responses. However, channel blockers do not emulate severe hypoxia, suggesting that hypoxia transduction procedes, at least in part, through an alternate pathway.

Chemoreceptor nerve excitation may not be proportional to catecholamine secretion

1996 ◽  
Vol 81 (2) ◽  
pp. 657-664 ◽  
Author(s):  
D. F. Donnelly
Keyword(s):  
Carotid Body ◽  
Catecholamine Secretion ◽  
Nerve Activity ◽  
Peripheral Chemoreceptor ◽  
Carotid Bodies ◽  
Carbon Fiber Microelectrodes ◽  
S Peak ◽  
Nerve Excitation ◽  
Catecholamine Levels

Enhanced catecholamine secretion from the carotid body glomus cells is hypothesized to play an essential role in mediating the peripheral chemoreceptor response to hypoxia. To test aspects of this hypothesis, the relationship between catecholamine secretion and nerve activity was examined during repetitive hypoxia stimuli and after catecholamine depletion with reserpine. Single-fiber afferent serve activity was measured along with an estimate of free tissue catecholamine by using Nafion-coated carbon-fiber microelectrodes placed in rat carotid bodies in vitro. Baseline and stimulated nerve and catecholamine levels were quantified during repetitive stimulation (anoxia of 1-min duration; PO2 = 0 Torr at nadir, repeated each 200 s). Peak stimulated catecholamine progressively decreased from 26.4 +/- 2.6 microM for the first stimulus to 7.5 +/- 0.9 microM for the fifth stimulus (n = 15), but peak nerve activity was much less affected (23.0 +/- 1.9 Hz, first trial; 19.9 +/- 1.4 Hz, fifth trial). An exposure to moderate hypoxia (approximately 80 Torr) before the repetitive anoxia stimuli produced catecholamine levels comparable to those obtained during repetitive anoxia, but peak nerve activity was significantly less (22.5 +/- 3.4 vs. 12.7 +/- 2.1 Hz). Pretreatment with reserpine (1 mg/100 g) resulted in a large reduction in the average hypoxia-induced catecholamine response (1.4 +/- 0.3 microM, n = 9), but peak nerve activity was not different from nontreated controls. These results demonstrate an independence between carotid body catecholamine secretion and nerve activity, suggesting that nerve excitation is, at least, partially mediated through pathways independent of granule secretion.

Characteristics of carotid body chemosensitivity in NADPH oxidase-deficient mice

2002 ◽  
Vol 282 (1) ◽  
pp. C27-C33 ◽  
Author(s):  
L. He ◽  
J. Chen ◽  
B. Dinger ◽  
K. Sanders ◽  
K. Sundar ◽  
...  
Keyword(s):  
Tyrosine Hydroxylase ◽  
Nadph Oxidase ◽  
Carotid Body ◽  
Gene Knockout ◽  
Type I ◽  
Type I Cells ◽  
Carotid Bodies ◽  
Marker Antigen ◽  
I Cells

Various heme-containing proteins have been proposed as primary molecular O2 sensors for hypoxia-sensitive type I cells in the mammalian carotid body. One set of data in particular supports the involvement of a cytochrome b NADPH oxidase that is commonly found in neutrophils. Subunits of this enzyme have been immunocytochemically localized in type I cells, and diphenyleneiodonium, an inhibitor of the oxidase, increases carotid body chemoreceptor activity. The present study evaluated immunocytochemical and functional properties of carotid bodies from normal mice and from mice with a disrupted gp91 phagocytic oxidase (gp91 phox ) DNA sequence gene knockout (KO), a gene that codes for a subunit of the neutrophilic form of NADPH oxidase. Immunostaining for tyrosine hydroxylase, a signature marker antigen for type I cells, was found in groups or lobules of cells displaying morphological features typical of the O2-sensitive cells in other species, and the incidence of tyrosine hydroxylase-immunopositive cells was similar in carotid bodies from both strains of mice. Studies of whole cell K+currents also revealed identical current-voltage relationships and current depression by hypoxia in type I cells dissociated from normal vs. KO animals. Likewise, hypoxia-evoked increases in intracellular Ca2+ concentration were not significantly different for normal and KO type I cells. The whole organ response to hypoxia was evaluated in recordings of carotid sinus nerve activity in vitro. In these experiments, responses elicited by hypoxia and by the classic chemoreceptor stimulant nicotine were also indistinguishable in normal vs. KO preparations. Our data demonstrate that carotid body function remains intact after sequence disruption of the gp91 phox gene. These findings are not in accord with the hypothesis that the phagocytic form of NADPH oxidase acts as a primary O2 sensor in arterial chemoreception.

Ion channels in spinal cord astrocytes in vitro. I. Transient expression of high levels of Na+ and K+ channels

1992 ◽  
Vol 68 (4) ◽  
pp. 985-1000 ◽  
Author(s):  
H. Sontheimer ◽  
J. A. Black ◽  
B. R. Ransom ◽  
S. G. Waxman
Keyword(s):  
Spinal Cord ◽  
Membrane Potentials ◽  
Resting Potential ◽  
K Channel ◽  
Na Channels ◽  
Patch Clamp Recording ◽  
K Channels ◽  
Na Currents ◽  
Channel Expression

1. Na+ and K+ channel expression was studied in cultured astrocytes derived from P--0 rat spinal cord using whole cell patch-clamp recording techniques. Two subtypes of astrocytes, pancake and stellate, were differentiated morphologically. Both astrocyte types showed Na+ channels and up to three forms of K+ channels at certain stages of in vitro development. 2. Both astrocyte types showed pronounced K+ currents immediately after plating. Stellate but not pancake astrocytes additionally showed tetrodotoxin (TTX)-sensitive inward Na+ currents, which displayed properties similar to neuronal Na+ currents. 3. Within 4-5 days in vitro (DIV), pancake astrocytes lost K(+)-current expression almost completely, but acquired Na+ currents in high densities (estimated channel density approximately 2-8 channels/microns2). Na+ channel expression in these astrocytes is approximately 10- to 100-fold higher than previously reported for glial cells. Concomitant with the loss of K+ channels, pancake astrocytes showed significantly depolarized membrane potentials (-28.1 +/- 15.4 mV, mean +/- SD), compared with stellate astrocytes (-62.5 +/- 11.9 mV, mean +/- SD). 4. Pancake astrocytes were capable of generating action-potential (AP)-like responses under current clamp, when clamp potential was more negative than resting potential. Both depolarizing and hyperpolarizing current injections elicited overshooting responses, provided that cells were current clamped to membrane potentials more negative than -70 mV. Anode-break spikes were evoked by large hyperpolarizations (less than -150 mV). AP-like responses in these hyperpolarized astrocytes showed a time course similar to neuronal APs under conditions of low K+ conductance. 5. In stellate astrocytes, AP-like responses were not observed, because the K+ conductance always exceeded Na+ conductance by at least a factor of 3. Thus stellate spinal cord astrocyte membranes are stabilized close to EK as previously reported for hippocampal astrocytes. 6. It is concluded that spinal cord pancake astrocytes are capable of synthesizing Na+ channels at densities that can, under some conditions, support electrogenesis. In vivo, however, AP-like responses are unlikely to occur because the cells' resting potential is too depolarized to allow current activation. Thus the absence of electrogenesis in astrocytes may be explained by two mechanisms: 1) a low Na-to-K conductance ratio, as in stellate spinal cord astrocytes and in other previously studied astrocyte preparations; or, 2) as described in detail in the companion paper, a mismatch between the h infinity curve and resting potential, which results in Na+ current inactivation in spinal cord pancake astrocytes.

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.

Proarrhythmic and antiarrhythmic actions of ion channel blockers on arrhythmias in the heart: model study

1996 ◽  
Vol 271 (1) ◽  
pp. H329-H356 ◽  
Author(s):  
T. R. Chay
Keyword(s):  
Bifurcation Analysis ◽  
Slow Inward Current ◽  
K Channel ◽  
Inactivation Kinetics ◽  
High Threshold ◽  
Channel Blockers ◽  
Ring Size ◽  
Class Iii ◽  
Inward Current

We explain why 1) some class I and IV antiarrhythmia drugs could exert proarrhythmic action, 2) some class III drugs are effective in controlling reentrant arrhythmias, and 3) cycle length (CL) oscillation is involved in the termination or initiation of reentry. To explain these phenomena, we employ the following three means: bifurcation analysis, simulation, and model construction. Antiarrhythmia drugs are modeled by varying maximal conductances of Na+, Ca2+, and time-dependent delayed rectifying and time-independent inward rectifying K+ channels in the Beeler-Reuter model, where the model cells are arranged in a ring. Bifurcation analysis predicts that there is a critical ring size (CRS) at which infinite ring behavior suddenly breaks down. Channel blockers can affect CRS in different manners: Na+ and Ca2+ blockers shorten CRS, whereas delayed rectifying K+ channel blockers and the inward K+ channel blockers lengthen CRS. This differential explains why some antiarrhythmia drugs are proarrhythmic (i.e., shorten CRS) whereas others are antiarrhythmic (i.e., lengthen CRS). Simulation is then used to investigate how the drugs affect reentrant rhythms in the neighborhood of the CRS. We find that, in this region, CL, conduction velocity, and action potential duration become oscillatory. As ring size shrinks, the pattern of the oscillation becomes more complex. When the ring shrinks to a certain size, reentry can no longer be sustained, and it terminates after a few oscillatory cycles. To explain the basic mechanism involved in CL oscillation, we then construct a minimal model that contains a low-threshold fast inward current and a high-threshold slow inward current. With this model, we show that the two inward currents, with vastly different activation and inactivation kinetics, cause CL oscillations. Our results thus give theoretical explanations for the experimental finding of Frame's group in canine atrial tricuspid ring in vitro that class IC drugs can bring about stable reentry from nonsustained transient reentry, whereas class III drugs transform stable reentry to complex oscillations in CL. Our results also support the result of Frame's group, in that, in "adjustable" tricuspid rings, CL oscillation becomes more complex and its period becomes shorter as an excitable gap is shortened.

scholarly journals A Conserved Arginine Residue in the Pore Region of an Inward Rectifier K Channel (IRK1) as an External Barrier for Cationic Blockers

1997 ◽  
Vol 110 (6) ◽  
pp. 665-677 ◽  
Author(s):  
Ravshan Z. Sabirov ◽  
Tomoko Tominaga ◽  
Akiko Miwa ◽  
Yasunobu Okada ◽  
Shigetoshi Oiki
Keyword(s):  
Open Channel ◽  
Single Channel ◽  
K Channel ◽  
Channel Blockers ◽  
Channel Activity ◽  
Wild Type ◽  
K Channels ◽  
Blocking Rate ◽  
External Barrier ◽  
Kir2.1 Channel

The number, sign, and distribution of charged residues in the pore-forming H5 domain for inward-rectifying K channels (IRK1) are different from the otherwise homologous H5 domains of other voltage-gated K channels. We have mutated Arg148, which is perfectly conserved in all inward rectifiers, to His in the H5 of IRK1 (Kir2.1). Channel activity was lost by the mutation, but coexpression of the mutant (R148H) along with the wild-type (WT) mRNA revealed populations of channels with reduced single-channel conductances. Long-lasting and flickery sublevels were detected exclusively for the coexpressed channels. These findings indicated that the mutant subunit formed hetero-oligomers with the WT subunit. The permeability ratio was altered by the mutation, while the selectivity sequence (K+ &gt; Rb+ &gt; NH4+ &gt;&gt; Na+) was preserved. The coexpression made the IRK1 channel more sensitive to extracellular block by Mg2+ and Ca2+, and turned this blockade from a voltage-independent to a -dependent process. The sensitivity of the mutant channels to Mg2+ was enhanced at higher pH and by an increased ratio of mutant:WT mRNA, suggesting that the charge on the Arg site controlled the sensitivity. The blocking rate of open channel blockers, such as Cs+ and Ba2+, was facilitated by coexpression without significant change in the steady state block. Evaluation of the electrical distance to the binding site for Mg2+ or Ca2+ and that to the barrier peak for block by Cs+ or Ba2+ suggest that Arg148 is located between the external blocking site for Mg2+ or Ca2+ and the deeper blocking site for Cs+ or Ba2+ in the IRK1 channel. It is concluded that Arg148 serves as a barrier to cationic blockers, keeping Mg2+ and Ca2+ out from the electric field of the membrane.

Transformation of renal tubule epithelial cells by simian virus-40 is associated with emergence of Ca2+-insensitive K+ channels and altered mitogenic sensitivity to K+ channel blockers

1992 ◽  
Vol 151 (1) ◽  
pp. 113-125 ◽  
Author(s):  
Jacques Teulon ◽  
Pierre M. Ronco ◽  
Monique Geniteau-Legendre ◽  
B�atrice Baudouin ◽  
Simone Estrade ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Renal Tubule ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
K Channel ◽  
Channel Blockers ◽  
K Channels

scholarly journals The myth of scorpion suicide: are scorpions insensitive to their own venom?

1998 ◽  
Vol 201 (18) ◽  
pp. 2625-2636
Author(s):  
C Legros ◽  
MF Martin-Eauclaire ◽  
D Cattaert
Keyword(s):  
Action Potential ◽  
Procambarus Clarkii ◽  
Scorpion Venom ◽  
K Channel ◽  
Muscle Fibres ◽  
Channel Blockers ◽  
Na Channels ◽  
Nerve Fibres ◽  
K Channels ◽  
Voltage Gated

The resistance of the scorpion Androctonus australis to its own venom, as well as to the venom of other species, was investigated. A comparison of the electrical and pharmacological properties of muscle and nerve fibres from Androctonus australis with those from the crayfish Procambarus clarkii enabled us to understand the lack of effect of scorpion venom (110-180 microg ml-1) and purified toxins, which are active on voltage-gated Na+ and K+ channels, Ca2+-activated K+ channels, on scorpion tissues. Voltage-clamp experiments showed that peptide K+ channel blockers from scorpion and snake have no effect on currents in muscle and nerve fibres from either scorpions or crayfish. The scorpion toxin kaliotoxin (KTX), a specific blocker of Kv1.1 and Kv1.3 K+ channels, had no effect on muscle fibres of A. australis (2 micromol l-1) or P. clarkii (400 nmol l-1). Similarly, charybdotoxin (ChTX) had no effect on the muscle fibres of A. australis (10 micromol l-1) or P. clarkii (200 nmol l-1) and neither did the snake toxin dendrotoxin (DTX) at concentrations of 100 nmol l-1 in A. australis and 200 nmol l-1 in P. clarkii. These three toxins (KTX, ChTX and DTX) did not block K+ currents recorded from nerve fibres in P. clarkii. The pharmacology of the K+ channels in these two arthropods did not conform to that previously described for K+ channels in other species. Current-clamp experiments clearly indicated that the venom of A. australis (50 microg ml-1) had no effect on the shape of the action potential recorded from nerve cord axons from A. australis. At a concentration of 50 microg ml-1, A. australis venom greatly prolonged the action potential in the crayfish giant axon. The absence of any effect of the anti-mammal &lt;IMG src="/images/symbols/&agr ;.gif" WIDTH="9" HEIGHT="12" ALIGN="BOTTOM" NATURALSIZEFLAG="3"&gt;-toxin AaH II (100 nmol l-1) and the anti-insect toxin AaH IT1 (100 nmol l-1) on scorpion nerve fibres revealed strong pharmacological differences between the voltage-gated Na+ channels of scorpion and crayfish. We conclude that the venom from A. australis is pharmacologically inactive on K+ channels and on voltage-sensitive Na+ channels from this scorpion.

Vasorelaxant and Antihypertensive Effects of Neferine in Rats: An In Vitro and In Vivo Study

Planta Medica ◽  
2020 ◽  
Vol 86 (07) ◽  
pp. 496-504 ◽  
Author(s):  
Piyawadee Wicha ◽  
Amnart Onsa-ard ◽  
Waraluck Chaichompoo ◽  
Apichart Suksamrarn ◽  
Chainarong Tocharus
Keyword(s):  
Nitric Oxide ◽  
Thoracic Aorta ◽  
Antihypertensive Effect ◽  
Soluble Guanylyl Cyclase ◽  
K Channel ◽  
Channel Blockers ◽  
Organ Bath ◽  
Hypertensive Rats

AbstractThe present study was performed to examine the antihypertensive effect of neferine in hypertensive rats and its relaxant mechanisms in isolated rat thoracic aorta. The antihypertensive effect was evaluated by tail-cuff methods on NG-nitro-L-arginine methyl ester (L-NAME) (40 mg/kg BW) 4-week hypertensive-induced hypertensive rats. The vasorelaxant effect and its mechanisms were studied by the organ bath technique in the thoracic aorta isolated from normotensive rats. The results indicated that the treatment of neferine (1 mg/kg and 10 mg/kg) markedly decreased the systolic blood pressure (SBP) when compared with the hypertension group (137.75 ± 10.14 mmHg and 132.23 ± 9.5 mmHg, respectively, p < 0.001), without affecting the heart rate. Moreover, neferine (10−12 − 10−4 M) exhibited concentration-dependent vasorelaxation in endothelium-intact rings (Emax values = 98.95 ± 0.66% and pD2 = 7.93 ± 0.28) and endothelium-denuded rings (Emax values = 90.61 ± 1.91% and pD2 = 6.85 ± 0.36). The effects of neferine were reduced by pre-incubation with L-NAME and 1H-[1,2,4]oxadiazolo[4,3-a] quinoxalin-1-one (ODQ) but not with pre-incubation with indomethacin and K+channel blockers. Neferine attenuated the contractions induced by phenylephrine and caffeine in a Ca2+-free solution and also inhibited in CaCl2- and phenylephrine-induced contracted rings. Our study suggests that neferine exhibited hypertensive potential, induced vasorelaxation through the endothelium nitric oxide synthase (eNOS)/nitric oxide (NO)/soluble guanylyl cyclase (sGC) pathway and involved the modulation of Ca2+ influx through Ca2+ channels and intracellular Ca2+ release from the sarcoplasmic reticulum.

Apical K+ conductance in maturing rabbit principal cell

1997 ◽  
Vol 272 (3) ◽  
pp. F397-F404 ◽  
Author(s):  
L. M. Satlin ◽  
L. G. Palmer
Keyword(s):  
Reversal Potential ◽  
Principal Cell ◽  
K Channel ◽  
Postnatal Life ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
K Channels ◽  
Inward Currents ◽  
K Secretion

Net K+ secretion is not detected in cortical collecting ducts (CCDs) isolated from newborn rabbits and perfused in vitro. To establish whether a low apical K+ permeability of the neonatal principal cell limits K+ secretion early in life, we used the patch-clamp technique in split-open CCDs isolated from maturing rabbits to study the properties and density of conducting K+ channels in principal cells. With KCl in the pipette and a NaCl solution warmed to 37 degrees C in the bath, inward currents with a conductance of approximately 42 pS were observed in 0% (0 out of 13 or 0/13), 10% (2/21), 18% (5/28), 29% (4/14), and 56% (10/18) of cell-attached patches obtained in 1-, 2-, 3-, 4-, and 5-wk-old animals, respectively. The conductance and reversal potential of this channel led us to suspect that it represented the low-conductance K+ channel previously described in the rat CCD by L. G. Palmer, L. Antonian, and G. Frindt (J. Gen. Physiol. 104: 693-710, 1994). The mean number of open channels per patch (NPo) increased progressively (P < 0.05) after birth, from 0 at 1 wk, to 0.06 +/- 0.04 at 2 wk, to 0.40 +/- 0.18 at 3 wk, to 0.74 +/- 0.41 at 4 wk, and to 1.06 +/- 0.28 at 5 wk. The increase in NPo appeared to be due primarily to a developmental increase in N, which is the number of channels; open probability, Po, remained constant at approximately 0.5 for all channels identified after the 2nd wk of life. The increase in number of conducting K+ channels during postnatal life is likely to contribute to the maturational increase in net K+ secretion in the CCDs.

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