scholarly journals Isoflurane Depresses the Response of Inspiratory Hypoglossal Motoneurons to Serotonin In Vivo 

2007 ◽  
Vol 106 (4) ◽  
pp. 736-745 ◽  
Author(s):  
Ivo F. Brandes ◽  
Edward J. Zuperku ◽  
Astrid G. Stucke ◽  
Francis A. Hopp ◽  
Danica Jakovcevic ◽  
...  
Keyword(s):  
Neuronal Response ◽  
Discharge Frequency ◽  
K Channel ◽  
Neuronal Membrane ◽  
Spontaneous Discharge ◽  
Channel Conductance ◽  
Membrane Hyperpolarization ◽  
K Channels ◽  
Hypoglossal Motoneurons

Background Endogenous serotonin (5-HT) provides important excitatory drive to inspiratory hypoglossal motoneurons (IHMNs). In vitro studies show that activation of postsynaptic 5-HT receptors decreases a leak K+ channel conductance and depolarizes hypoglossal motoneurons (HMNs). In contrast, volatile anesthetics increase this leak K+ channel conductance, which causes neuronal membrane hyperpolarization and depresses HMN excitability. Clinical studies show upper airway obstruction, indicating HMN depression, even at subanesthetic concentrations. The authors hypothesized that if anesthetic activation of leak K+ channels caused neuronal depression in vivo, this effect could be antagonized with serotonin. In this case, the neuronal response to picoejected serotonin would be greater during isoflurane than with no isoflurane. Methods Studies were performed in decerebrate, vagotomized, paralyzed, and mechanically ventilated dogs during hypercapnic hyperoxia. The authors studied the effect of approximately 0.3 minimum alveolar concentration (MAC) isoflurane on the spontaneous discharge frequency patterns of single IHMNs and on the neuronal response to picoejection of 5-HT. Results Normalized data (mean +/- SD, n = 19) confirmed that 0.3 +/- 0.1 MAC isoflurane markedly reduced the spontaneous peak discharge frequency by 48 +/- 19% (P < 0.001) and depressed the slope of the spontaneous discharge patterns. The increase in neuronal frequency in response to 5-HT was reduced by 34 +/- 22% by isoflurane (P < 0.001). Conclusion Subanesthetic concentrations of isoflurane strongly depressed canine IHMNs in vivo. The neuronal response to 5-HT was also depressed by isoflurane, suggesting that anesthetic activation of leak K+ channels, which is expected to result in a larger 5-HT response, was not a dominant mechanism in this depression.

Basolateral potassium channels in renal proximal tubule

1987 ◽  
Vol 253 (3) ◽  
pp. F476-F487 ◽  
Author(s):  
H. Sackin ◽  
L. G. Palmer
Keyword(s):  
Single Channel ◽  
Basolateral Membrane ◽  
K Channel ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
K Channels ◽  
Open Time ◽  
Excised Patches ◽  
The Mean ◽  
Inside Out

Potassium (K+) channels in the basolateral membrane of unperfused Necturus proximal tubules were studied in both cell-attached and excised patches, after removal of the tubule basement membrane by manual dissection without collagenase. Two different K+ channels were identified on the basis of their kinetics: a short open-time K+ channel, with a mean open time less than 1 ms, and a long open-time K+ channel with a mean open time greater than 20 ms. The short open-time channel occurred more frequently than the longer channel, especially in excised patches. For inside-out excised patches with Cl- replaced by gluconate, the current-voltage relation of the short open-time K+ channel was linear over +/- 60 mV, with a K+-Na+ selectivity of 12 +/- 2 (n = 12), as calculated from the reversal potential with oppositely directed Na+ and K+ gradients. With K-Ringer in the patch pipette and Na-Ringer in the bath, the conductance of the short open-time channel was 47 +/- 2 pS (n = 15) for cell-attached patches, 26 +/- 2 pS (n = 15) for patches excised (inside out) into Na-Ringer, and 36 +/- 6 pS (n = 3) for excised patches with K-Ringer on both sides. These different conductances can be partially explained by a dependence of single-channel conductance on the K+ concentration on the interior side of the membrane. In experiments with a constant K+ gradient across excised patches, large changes in Na+ at the interior side of the membrane produced no change in single-channel conductance, arguing against a direct block of the K+ channel by Na+. Finally, the activity of the short open-time channel was voltage gated, where the mean number of open channels decreased as a linear function of basolateral membrane depolarization for potentials between -60 and 0 mV. Depolarization from -60 to -40 mV decreased the mean number of open K+ channels by 28 +/- 8% (n = 6).

scholarly journals Low molecular weight poly(A)+ mRNA species encode factors that modulate gating of a non-Shaker A-type K+ channel.

1993 ◽  
Vol 102 (4) ◽  
pp. 713-728 ◽  
Author(s):  
L D Chabala ◽  
N Bakry ◽  
M Covarrubias
Keyword(s):  
Molecular Weight ◽  
Xenopus Oocytes ◽  
Membrane Potentials ◽  
K Channel ◽  
Low Molecular Weight ◽  
K Channels ◽  
Fourfold Increase ◽  
Mrna Species ◽  
Type K

Voltage-dependent K+ channels control repolarization of action potentials and help establish firing patterns in nerve cells. To determine the nature and role of molecular components that modulate K+ channel function in vivo, we coinjected Xenopus oocytes with cRNA encoding a cloned subthreshold A-type K+ channel (mShal1, also referred to as mKv4.1) and a low molecular weight (LMW) fraction (2-4 kb) of poly(A)+ mRNA (both from rodent brain). Coinjected oocytes exhibited a significant (fourfold) increase in the surface expression of mShal1 K+ channels with no change in the open-channel conductance. Coexpression also modified the gating kinetics of mShal1 current in several respects. Macroscopic inactivation of whole oocyte currents was fitted with the sum of two exponential components. Both fast and slow time constants of inactivation were accelerated at all membrane potentials in coinjected oocytes (tau f = 47.2 ms vs 56.5 ms at 0 mV and tau s = 157 ms vs 225 ms at 0 mV), and the corresponding ratios of amplitude terms were shifted toward domination by the fast component (Af/As = 2.71 vs 1.17 at 0 mV). Macroscopic activation was characterized in terms of the time-to-peak current, and it was found to be more rapid at all membrane potentials in coinjected oocytes (9.9 ms vs 13.5 ms at 0 mV). Coexpression also leads to more rapid recovery from inactivation (approximately 2.4-fold faster at -100 mV). The coexpressed K+ currents in oocytes resemble currents expressed in mouse fibroblasts (NIH3T3) transfected only with mShal1 cDNA. These results indicate that mammalian regulatory subunits or enzymes encoded by LMW mRNA species, which are apparently missing or expressed at low levels in Xenopus oocytes, may modulate gating in some native subthreshold A-type K+ channels.

scholarly journals Pharmacological and kinetic analysis of K channel gating currents.

1989 ◽  
Vol 93 (2) ◽  
pp. 263-283 ◽  
Author(s):  
S Spires ◽  
T Begenisich
Keyword(s):  
Channel Gating ◽  
K Channel ◽  
Na Channel ◽  
Gating Current ◽  
Channel Conductance ◽  
Gating Currents ◽  
Current Time ◽  
Time Constants ◽  
K Channels ◽  
Low Concentrations

We have measured gating currents from the squid giant axon using solutions that preserve functional K channels and with experimental conditions that minimize Na channel contributions to these currents. Two pharmacological agents were used to identify a component of gating current that is associated with K channels. Low concentrations of internal Zn2+ that considerably slow K channel ionic currents with no effect on Na channel currents altered the component of gating current associated with K channels. At low concentrations (10-50 microM) the small, organic, dipolar molecule phloretin has several reported specific effects on K channels: it reduces K channel conductance, shifts the relationship between channel conductance and membrane voltage (Vm) to more positive potentials, and reduces the voltage dependence of the conductance-Vm relation. The K channel gating charge movements were altered in an analogous manner by 10 microM phloretin. We also measured the dominant time constants of the K channel ionic and gating currents. These time constants were similar over part of the accessible voltage range, but at potentials between -40 and 0 mV the gating current time constants were two to three times faster than the corresponding ionic current values. These features of K channel function can be reproduced by a simple kinetic model in which the channel is considered to consist of two, two-state, nonidentical subunits.

Venoconstriction to endothelin-1 in humans: role of calcium and potassium channels

1993 ◽  
Vol 265 (5) ◽  
pp. H1676-H1681 ◽  
Author(s):  
W. G. Haynes ◽  
D. J. Webb
Keyword(s):  
Human Subjects ◽  
K Channel ◽  
K Channels ◽  
Endothelin 1 ◽  
Channel Opener ◽  
K Channel Opener ◽  
Ca2 Channels

Recent studies in vitro have suggested that there may be an interaction between endothelin-1 and ATP-sensitive K+ channels in vascular smooth muscle. Here we have investigated whether agents acting on membrane Ca2+ and K+ channels modulate endothelin-1-induced venoconstriction in vivo in human subjects. In a series of studies, six healthy subjects received, on separate occasions, local infusions into dorsal hand veins of endothelin-1 coinfused with 1) the ATP-sensitive K+ channel opener, cromakalim; 2) the dihydropyridine Ca2+ antagonist, nicardipine; 3) a control vasodilator, hydralazine; and 4) saline placebo. Endothelin-1 caused local venoconstriction with a maximum reduction in vein size of 66 +/- 4% at 60 min (P = 0.0001 vs. basal). Cromakalim prevented endothelin-1-induced venoconstriction (9 +/- 10% maximum constriction; P = 0.68 vs. basal). By contrast, nicardipine, in a dose sufficient to block depolarization-induced constriction caused by K+ infusion, had only a partial effect on endothelin-1-induced venoconstriction (35 +/- 8% maximum constriction; P = 0.001 vs. basal; P = 0.02 vs. endothelin-1), whereas a 10-fold higher dose of nicardipine had no additional effect and hydralazine had no effect. In further studies, cromakalim, but not nicardipine, reversed endothelin-1-induced venoconstriction. Cromakalim did not prevent constriction induced by norepinephrine. Although calcium entry through dihydropyridine-sensitive Ca2+ channels may account in part for the vasoconstrictor action of endothelin-1 in humans, the abolition of endothelin-1 responses by a K+ channel opener suggests additional mechanisms of action for endothelin-1.

Electrical characteristics of inward-rectifying K+ channels in isolated bullfrog oxyntic cells

1991 ◽  
Vol 261 (2) ◽  
pp. G206-G212 ◽  
Author(s):  
H. Mieno ◽  
G. Kajiyama
Keyword(s):  
Single Channel ◽  
Rana Catesbeiana ◽  
Basolateral Membrane ◽  
Inward Rectification ◽  
K Channel ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Open Probability ◽  
K Channels ◽  
Patch Clamp Method

The properties of K+ channels in the isolated oxyntic cells of the bullfrog (Rana catesbeiana) were investigated using the patch-clamp method. Two types of K+ channels on the basolateral membrane were identified on the basis of their electrophysiological and pharmacological properties. The K+ channel most frequently observed has a single-channel conductance of 61.0 +/- 2.9 pS (n = 10) and is activated by an increase in intracellular Ca2+. The other K+ channel has a single-channel conductance of 30.3 +/- 2.7 pS (n = 7), which is activated by adenosine 3',5'-cyclic monophosphate (cAMP). The physiological and pharmacological characteristics common to the two K+ channels are inward-going rectification with a high selectivity for K+ and indirect inhibition by omeprazole. The inward rectification is controlled by intracellular Mg2+ in such a way that the more Mg2+ is applied intracellularly, the more their inward-rectifying property is enhanced. The finding that bethanechol and cAMP increase the open probability of these K+ channels as well as activating the acid secretion indicates that there may be a relationship between these two processes in the oxyntic cells.

scholarly journals Trapping of a Methanesulfonanilide by Closure of the Herg Potassium Channel Activation Gate

2000 ◽  
Vol 115 (3) ◽  
pp. 229-240 ◽  
Author(s):  
John S. Mitcheson ◽  
Jun Chen ◽  
Michael C. Sanguinetti
Keyword(s):  
Single Channel ◽  
K Channel ◽  
Membrane Hyperpolarization ◽  
K Channels ◽  
Large Size ◽  
Channel Opening ◽  
Activated State ◽  
Activation Gate ◽  
Herg Channels ◽  
Positively Charged

Deactivation of voltage-gated potassium (K+) channels can slow or prevent the recovery from block by charged organic compounds, a phenomenon attributed to trapping of the compound within the inner vestibule by closure of the activation gate. Unbinding and exit from the channel vestibule of a positively charged organic compound should be favored by membrane hyperpolarization if not impeded by the closed gate. MK-499, a methanesulfonanilide compound, is a potent blocker (IC50 = 32 nM) of HERG K+ channels. This bulky compound (7 × 20 Å) is positively charged at physiological pH. Recovery from block of HERG channels by MK-499 and other methanesulfonanilides is extremely slow (Carmeliet 1992; Ficker et al. 1998), suggesting a trapping mechanism. We used a mutant HERG (D540K) channel expressed in Xenopus oocytes to test the trapping hypothesis. D540K HERG has the unusual property of opening in response to hyperpolarization, in addition to relatively normal gating and channel opening in response to depolarization (Sanguinetti and Xu 1999). The hyperpolarization-activated state of HERG was characterized by long bursts of single channel reopening. Channel reopening allowed recovery from block by 2 μM MK-499 to occur with time constants of 10.5 and 52.7 s at −160 mV. In contrast, wild-type HERG channels opened only briefly after membrane hyperpolarization, and thus did not permit recovery from block by MK-499. These findings provide direct evidence that the mechanism of slow recovery from HERG channel block by methanesulfonanilides is due to trapping of the compound in the inner vestibule by closure of the activation gate. The ability of HERG channels to trap MK-499, despite its large size, suggests that the vestibule of this channel is larger than the well studied Shaker K+ channel.

Pharmacological coupling and functional role for CGRP receptors in the vasodilation of rat pial arterioles

1996 ◽  
Vol 270 (1) ◽  
pp. H317-H323 ◽  
Author(s):  
K. W. Hong ◽  
S. E. Yoo ◽  
S. S. Yu ◽  
J. Y. Lee ◽  
B. Y. Rhim
Keyword(s):  
Channel Blocker ◽  
K Channel ◽  
Receptor Subtype ◽  
Camp Production ◽  
K Channels ◽  
Cranial Window ◽  
Pial Arterioles ◽  
Vasodilator Action

In this study, we investigated the signal transduction underlying the vasodilator action of calcitonin gene-related peptide (CGRP) in the rat pial arterioles. In an in vivo experiment, changes in pial arterial diameters (20.2 +/- 1.9 microns) were observed under suffusion with mock cerebrospinal fluid containing CGRP (10(-9)-10(-7) M) directly through a closed cranial window. Changes in intracellular adenosine 3',5'-cyclic monophosphate (cAMP) accumulation in response to CGRP and levcromakalim were measured in the pial arterioles in an in vitro experiment. CGRP-induced vasodilation and cAMP production were significantly inhibited by specific CGRP antibody serum and CGRP-(8-37) fragment, suggesting involvement of the CGRP1 receptor subtype. Vasodilation and increase in cAMP production evoked by CGRP were inhibited not only by glibenclamide (ATP-sensitive K+ channel blocker) but also by charybdotoxin (large-conductance Ca(2+)-activated K+ channel blocker), but this was not the case for the isoproterenol-induced vasodilation and cAMP production. These findings implicate the ATP-sensitive K+ channels and the large-conductance Ca(2+)-activated K+ channels in the CGRP receptor-coupled cAMP production for vasodilation. Further study is required to identify whether the cAMP-dependent K+ channel activation is related to CGRP-induced vasorelaxation of the rat pial arterioles.

scholarly journals PSD-95 and SAP97 Exhibit Distinct Mechanisms for Regulating K+ Channel Surface Expression and Clustering

2000 ◽  
Vol 148 (1) ◽  
pp. 147-157 ◽  
Author(s):  
Amanda M. Tiffany ◽  
Louis N. Manganas ◽  
Eunjoon Kim ◽  
Yi-Ping Hsueh ◽  
Morgan Sheng ◽  
...  
Keyword(s):  
Cell Surface ◽  
Ion Channel ◽  
Membrane Vesicles ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
K Channel ◽  
Neuronal Membrane ◽  
K Channels ◽  
Kv Channels ◽  
Abundance And Distribution

Mechanisms of ion channel clustering by cytoplasmic membrane-associated guanylate kinases such as postsynaptic density 95 (PSD-95) and synapse-associated protein 97 (SAP97) are poorly understood. Here, we investigated the interaction of PSD-95 and SAP97 with voltage-gated or Kv K+ channels. Using Kv channels with different surface expression properties, we found that clustering by PSD-95 depended on channel cell surface expression. Moreover, PSD-95–induced clusters of Kv1 K+ channels were present on the cell surface. This was most dramatically demonstrated for Kv1.2 K+ channels, where surface expression and clustering by PSD-95 were coincidentally promoted by coexpression with cytoplasmic Kvβ subunits. Consistent with a mechanism of plasma membrane channel–PSD-95 binding, coexpression with PSD-95 did not affect the intrinsic surface expression characteristics of the different Kv channels. In contrast, the interaction of Kv1 channels with SAP97 was independent of Kv1 surface expression, occurred intracellularly, and prevented further biosynthetic trafficking of Kv1 channels. As such, SAP97 binding caused an intracellular accumulation of each Kv1 channel tested, through the accretion of SAP97 channel clusters in large (3–5 μm) ER-derived intracellular membrane vesicles. Together, these data show that ion channel clustering by PSD-95 and SAP97 occurs by distinct mechanisms, and suggests that these channel-clustering proteins may play diverse roles in regulating the abundance and distribution of channels at synapses and other neuronal membrane specializations.

scholarly journals Involvement of BKCa and KV Potassium Channels in cAMP-Induced Vasodilatation: Their Insufficient Function in Genetic Hypertension

2014 ◽  
pp. 275-285
Author(s):  
M. PINTÉROVÁ ◽  
M. BEHULIAK ◽  
J. KUNEŠ ◽  
J. ZICHA
Keyword(s):  
No Synthase ◽  
K Channel ◽  
Spontaneously Hypertensive ◽  
K Channels ◽  
Wky Rats ◽  
Genetic Hypertension ◽  
Kv Channels ◽  
Adrenoceptor Agonist ◽  
Vasodilator Action

Spontaneously hypertensive rats (SHR) are characterized by enhanced sympathetic vasoconstriction, whereas their vasodilator mechanisms are relatively attenuated compared to their high BP. The objective of our in vivo study was to evaluate whether the impaired function of BKCa and/or KV channels is responsible for abnormal cAMP-induced vasodilatation in genetic hypertension. Using conscious SHR and normotensive WKY rats we have shown that under the basal conditions cAMP overproduction elicited by the infusion of β-adrenoceptor agonist (isoprenaline) caused a more pronounced decrease of baseline blood pressure (BP) in SHR compared to WKY rats. Isoprenaline infusion prevented BP rises induced by acute NO synthase blockade in both strains and it also completely abolished the fully developed BP response to NO synthase blockade. These cAMP-induced vasodilator effects were diminished by the inhibition of either BKCa or KV channels in SHR but simultaneous blockade of both K+ channel types was necessary in WKY rats. Under basal conditions, the vasodilator action of both K+ channels was enhanced in SHR compared to WKY rats. However, the overall contribution of K+ channels to cAMP-induced vasodilator mechanisms is insufficient in genetic hypertension since a concurrent activation of both K+ channels by cAMP overproduction is necessary for the prevention of BP rise elicited by acute NO/cGMP deficiency in SHR. This might be caused by less effective activation of these K+ channels by cAMP in SHR. In conclusion, K+ channels seem to have higher activity in SHR, but their vasodilator action cannot match sufficiently the augmented vasoconstriction in this hypertensive strain.

Ca(2+)-dependent and Ca(2+)-permeable ion channels in aortic endothelial cells

1992 ◽  
Vol 263 (6) ◽  
pp. H1827-H1838 ◽  
Author(s):  
B. N. Ling ◽  
W. C. O'Neill
Keyword(s):  
Endothelial Cells ◽  
Ion Channels ◽  
K Channel ◽  
Membrane Hyperpolarization ◽  
Aortic Endothelial Cells ◽  
K Channels ◽  
Initial Activation ◽  
Inwardly Rectifying ◽  
Inside Out ◽  
Aortic Endothelial

We investigated whether osmotic stress would activate specific ion channels in bovine aortic endothelial cells (BAECs). In isotonic medium (290 mosmol/kgH2O), cell-attached patch recordings contained both 165-pS K+ channels activated by depolarization and 40-pS K+ channels activated by 200 nM bradykinin. These inwardly rectifying K+ channels were activated by raising “cytoplasmic” Ca2+ in inside-out patches. BAEC exposed to hypotonic bath (220 mosmol/kg) exhibited a 20% decrease in intracellular K+ content within 5 min. Cell-attached patches revealed biphasic K+ channel activation with hypotonic exposure; initial activation of 165- and 40-pS K+ channels (1–3 min) was followed by a delayed but sustained reactivation of both K+ channels (> 5 min). The delayed reactivation phase was dependent on the presence of external Ca2+ and was attenuated by 10 microM gadolinium. A 28-pS nonselective cation channel (NSCC), which conducted inward Ca2+ current, was also detected during hypotonic exposure. This NSCC was stimulated by hyperpolarization and was blocked by 10 microM gadolinium. In BAEC 1) hypotonic exposure activates Ca(2+)-dependent, 165- and 40-pS K+ channels biphasically; 2) the initial phase is independent of external Ca2+, while the delayed phase requires external Ca2+; and 3) Ca(2+)-permeable, 28-pS NSCCs stimulated by membrane hyperpolarization provide a pathway for external Ca2+ influx.

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