Local Anesthetics Modulate Neuronal Calcium Signaling through Multiple Sites of Action

2003 ◽  
Vol 98 (5) ◽  
pp. 1139-1146 ◽  
Author(s):  
Fang Xu ◽  
Zayra Garavito-Aguilar ◽  
Esperanza Recio-Pinto ◽  
Jin Zhang ◽  
Thomas J. J. Blanck
Keyword(s):  
Local Anesthetics ◽  
K Channel ◽  
Na Channels ◽  
Channel Blockade ◽  
K Channels ◽  
Voltage Dependent ◽  
Sites Of Action ◽  
A Site ◽  
Ca2 Channels

Background Local anesthetics (LAs) are known to inhibit voltage-dependent Na+ channels, as well as K+ and Ca2+ channels, but with lower potency. Since cellular excitability and responsiveness are largely determined by intracellular Ca2+ availability, sites along the Ca2+ signaling pathways may be targets of LAs. This study was aimed to investigate the LA effects on depolarization and receptor-mediated intracellular Ca2+ changes and to examine the role of Na+ and K+ channels in such functional responses. Methods Effects of bupivacaine, ropivacaine, mepivacaine, and lidocaine (0.1-2.3 mm) on evoked [Ca2+](i) transients were investigated in neuronal SH-SY5Y cell suspensions using Fura-2 as the intracellular Ca2+ indicator. Potassium chloride (KCl, 100 mm) and carbachol (1 mm) were individually or sequentially applied to evoke increases in intracellular Ca2+. Coapplication of LA and Na+/K+ channel blockers was used to evaluate the role of Na+ and K+ channels in the LA effect on the evoked [Ca2+](i) transients. Results All four LAs concentration-dependently inhibited both KCl- and carbachol-evoked [Ca2+](i) transients with the potency order bupivacaine > ropivacaine > lidocaine >/= mepivacaine. The carbachol-evoked [Ca2+](i) transients were more sensitive to LAs without than with a KCl prestimulation, whereas the LA-effect on the KCl-evoked [Ca2+](i) transients was not uniformly affected by a carbachol prestimulation. Na+ channel blockade did not alter the evoked [Ca2+](i) transients with or without a LA. In the absence of LA, K+ channel blockade increased the KCl-, but decreased the carbachol-evoked [Ca2+](i) transients. A coapplication of LA and K+ channel blocker resulted in larger inhibition of both KCl- and carbachol-evoked [Ca2+](i) transients than by LA alone. Conclusions Different and overlapping sites of action of LAs are involved in inhibiting the KCl- and carbachol-evoked [Ca2+](i) transients, including voltage-dependent Ca2+ channels, a site associated with the caffeine-sensitive Ca2+ store and a possible site associated with the IP(3)-sensitive Ca2+ store, and a site in the muscarinic pathway. K+ channels, but not Na+ channels, seem to modulate the evoked [Ca2+](i) transients, as well as the LA-effects on such responses.

An active membrane model of the cerebellar Purkinje cell. I. Simulation of current clamps in slice

1994 ◽  
Vol 71 (1) ◽  
pp. 375-400 ◽  
Author(s):  
E. De Schutter ◽  
J. M. Bower
Keyword(s):  
Purkinje Cell ◽  
Ionic Channels ◽  
K Channel ◽  
Na Channels ◽  
Plateau Potentials ◽  
Spike Generation ◽  
K Channels ◽  
Voltage Dependent ◽  
P Type ◽  
Ca2 Channels

1. A detailed compartmental model of a cerebellar Purkinje cell with active dendritic membrane was constructed. The model was based on anatomic reconstructions of single Purkinje cells and included 10 different types of voltage-dependent channels described by Hodgkin-Huxley equations, derived from Purkinje cell-specific voltage-clamp data where available. These channels included a fast and persistent Na+ channel, three voltage-dependent K+ channels, T-type and P-type Ca2+ channels, and two types of Ca(2+)-activated K+ channels. 2. The ionic channels were distributed differentially over three zones of the model, with Na+ channels in the soma, fast K+ channels in the soma and main dendrite, and Ca2+ channels and Ca(2+)-activated K+ channels in the entire dendrite. Channel densities in the model were varied until it could reproduce Purkinje cell responses to current injections in the soma or dendrite, as observed in slice recordings. 3. As in real Purkinje cells, the model generated two types of spiking behavior. In response to small current injections the model fired exclusively fast somatic spikes. These somatic spikes were caused by Na+ channels and repolarized by the delayed rectifier. When higher-amplitude current injections were given, sodium spiking increased in frequency until the model generated large dendritic Ca2+ spikes. Analysis of membrane currents underlying this behavior showed that these Ca2+ spikes were caused by the P-type Ca2+ channel and repolarized by the BK-type Ca(2+)-activated K+ channel. As in pharmacological blocking experiments, removal of Na+ channels abolished the fast spikes and removal of Ca2+ channels removed Ca2+ spiking. 4. In addition to spiking behavior, the model also produced slow plateau potentials in both the dendrite and soma. These longer-duration potentials occurred in response to both short and prolonged current steps. Analysis of the model demonstrated that the plateau potentials in the soma were caused by the window current component of the fast Na+ current, which was much larger than the current through the persistent Na+ channels. Plateau potentials in the dendrite were carried by the same P-type Ca2+ channel that was also responsible for Ca2+ spike generation. The P channel could participate in both model functions because of the low-threshold K2-type Ca(2+)-activated K+ channel, which dynamically changed the threshold for dendritic spike generation through a negative feedback loop with the activation kinetics of the P-type Ca2+ channel. 5. These model responses were robust to changes in the densities of all of the ionic channels.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Role of Ca2+ and Na+ on luteinizing hormone release from the calf pituitary

1988 ◽  
Vol 255 (4) ◽  
pp. E469-E474
Author(s):  
J. P. Kile ◽  
M. S. Amoss
Keyword(s):  
Luteinizing Hormone ◽  
Ionophore A23187 ◽  
Channel Blockers ◽  
Hormone Release ◽  
Primary Cells ◽  
Rat Pituitary ◽  
Voltage Dependent ◽  
Lh Release ◽  
Ca2 Channels

It has been proposed that gonadotropin-releasing hormone (GnRH) stimulates Ca2+ entry by activation of voltage-independent, receptor-mediated Ca2+ channels in the rat gonadotroph. Little work has been done on the role of calcium in GnRH-induced luteinizing hormone (LH) release in species other than the rat. Therefore, this study was done to compare the effects of agents that alter Ca2+ or Na+ entry on LH release from calf anterior pituitary primary cells in culture. GnRH (100 ng/ml), Ca2+ ionophore A23187 (2.5 microM), and the depolarizing agent ouabain (0.1-10 microM) all produced significant increases (P less than 0.05) in LH release; these effects were significantly reduced when the cells were preincubated with the organic Ca2+ channel blockers nifedipine (1-10 microM) and verapamil (1-10 microM) and with Co2+ (0.01-1 mM). The effect of ouabain was inhibited by tetrodotoxin (TTX; 1-10 nM) as well as by nifedipine at 0.1-10 microM. In contrast to its effect on rat pituitary LH release, TTX significantly inhibited GnRH-stimulated LH release at 1-100 nM. These results suggest that GnRH-induced LH release may employ Ca2+ as a second messenger in bovine gonadotrophs and support recent speculation that GnRH-induced Ca2+ mobilization may in part be voltage dependent.

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.

Hyperexcitability at sites of nerve injury depends on voltage-sensitive Na+ channels

1994 ◽  
Vol 72 (1) ◽  
pp. 349-359 ◽  
Author(s):  
O. Matzner ◽  
M. Devor
Keyword(s):  
Nerve Injury ◽  
Duty Cycle ◽  
Firing Frequency ◽  
Na Channel ◽  
Channel Blockers ◽  
Na Channels ◽  
Experimental Conditions ◽  
K Channels ◽  
Inward Currents ◽  
Ca2 Channels

1. We used the tested fiber method to record from single myelinated afferents axons ending in a chronic nerve injury site (neuroma) in the rat sciatic nerve or L4,5 dorsal root. Axons were chosen for study that fired spontaneously with a stable tonic or interrupted (bursty) autorhythmic firing pattern. 2. Agents that block voltage-sensitive Na+ channels [tetrodotoxin (TTX), lidocaine], voltage-sensitive Ca2+ channels (Cd2+, Co2+, Ni2+, verapamil, D600, nifedipine, and fluarizine), volt-age-sensitive K+ channels [tetraethylammonium (TEA), 4-aminopyridine (4-AP)], and Ca(2+)-activated K+ channels (gK+Ca2+;quinidine, apamine) were applied topically to the neuroma. Effects on baseline rhythmogenesis and on the duty cycle of bursting were documented. Spike pattern analysis was used to determine whether changes in firing frequency were associated with changes in impulse initiation (electrogenesis), or resulted from (partial) block of impulse propagation downstream from the site of electrogenesis. Effects of veratridine were also noted. 3. Na+ channel blockers consistently quenched neuroma firing, and they did so by suppressing the process of impulse initiation. Only rarely was propagation block the dominant process. In bursty fibers the duration of on-periods shortened as the duration of off-periods lengthened, without a significant change in the baseline interspike interval (ISI). Veratridine accelerated firing, also via the impulse generating process. 4. Ca2+ channel blockers had essentially no effect on baseline firing rate (i.e., ISI). 5. Ca2+ channel blockers, as well as blockers of gK+Ca2+, had substantial, but inconsistent effects on burst pattern. It is not clear whether this reflects variability in the experimental conditions, or heterogeneity among the fibers sampled. 6. Blockade of K+ channels failed to evoke rhythmogenesis in acutely cut axons as it does in chronically injured axons, even in the presence of veratridine. This is consistent with other evidence that ectopic neuroma firing depends on postinjury remodeling of membrane electrical properties. 7. The data indicate that, in chronically injured axons, the inward currents that underly electrogenicity, enable ectopic discharge, and, together with outward K+ currents, set the fundamental firing rhythm (ISI), operate primarily with the use of voltage-sensitive Na+ rather than Ca2+ channels. 8. The on-off duty cycle in bursty fibers was affected by Na+ channel ligands and also, although less so, and less consistently by, Ca2+ channel ligands. This indicates that both may play a role in the slow modulations of membrane potential that presumably underly interrupted autorhythmicity.

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.

Essential role of oligodendrocytes in the formation and maintenance of central nervous system nodal regions

Development ◽  
2001 ◽  
Vol 128 (23) ◽  
pp. 4881-4890 ◽  
Author(s):  
Carole Mathis ◽  
Natalia Denisenko-Nehrbass ◽  
Jean-Antoine Girault ◽  
Emiliana Borrelli
Keyword(s):  
Na Channels ◽  
Myelinated Axons ◽  
K Channels ◽  
Protein Levels ◽  
Ankyrin G ◽  
Specific Proteins ◽  
Jimpy Mice ◽  
The Brain

The membrane of myelinated axons is divided into functionally distinct domains characterized by the enrichment of specific proteins. The mechanisms responsible for this organization have not been fully identified. To further address the role of oligodendrocytes in the functional segmentation of the axolemma in vivo, the distribution of nodal (Na+ channels, ankyrin G), paranodal (paranodin/contactin-associated-protein) and juxtaparanodal (Kv1.1 K+ channels) axonal markers, was studied in the brain of MBP-TK and jimpy mice. In MBP-TK transgenic mice, oligodendrocyte ablation was selectively induced by FIAU treatment before and during the onset of myelination. In jimpy mice, oligodendrocytes degenerate spontaneously within the first postnatal weeks after the onset of myelination. Interestingly, in MBP-TK mice treated for 1-20 days with FIAU, despite the ablation of more than 95% of oligodendrocytes, the protein levels of all tested nodal markers was unaltered. Nevertheless, these proteins failed to cluster in the nodal regions. By contrast, in jimpy mice, despite a diffused localization of paranodin, the formation of nodal clusters of Na+ channels and ankyrin G was observed. Furthermore, K+ channels clusters were transiently visible, but were in direct contact with nodal markers. These results demonstrate that the organization of functional domains in myelinated axons is oligodendrocyte dependent. They also show that the presence of these cells is a requirement for the maintenance of nodal and paranodal regions.

Ba2+, TEA+, and quinine effects on apical membrane K+ conductance and maxi K+ channels in gallbladder epithelium

1990 ◽  
Vol 259 (1) ◽  
pp. C56-C68 ◽  
Author(s):  
Y. Segal ◽  
L. Reuss
Keyword(s):  
Apical Membrane ◽  
Membrane Conductance ◽  
Membrane Resistance ◽  
K Channel ◽  
Dependent Manner ◽  
Gallbladder Epithelium ◽  
Concentration Dependent Manner ◽  
K Channels ◽  
Voltage Dependent ◽  
Channel Currents

The apical membrane of Necturus gallbladder epithelium contains a voltage-activated K+ conductance [Ga(V)]. Large-conductance (maxi) K+ channels underlie Ga(V) and account for 17% of the membrane conductance (Ga) under control conditions. We examined the Ba2+, tetraethylammonium (TEA+), and quinine sensitivities of Ga and single maxi K+ channels. Mucosal Ba2+ addition decreased resting Ga in a concentration-dependent manner (65% block at 5 mM) and decreased Ga(V) in a concentration- and voltage-dependent manner. Mucosal TEA+ addition also decreased control Ga (60% reduction at 5 mM). TEA+ block of Ga(V) was more potent and less voltage dependent that Ba2+ block. Maxi K+ channels were blocked by external Ba2+ at millimolar levels and by external TEA+ at submillimolar levels. At 0.3 mM, quinine (mucosal addition) hyperpolarized the cell membranes by 6 mV and reduced the fractional apical membrane resistance by 50%, suggesting activation of an apical membrane K+ conductance. At 1 mM, quinine both activated and blocked K(+)-conductive pathways. Quinine blocked maxi K+ channel currents at submillimolar concentrations. We conclude that 1) Ba2+ and TEA+ block maxi K+ channels and other K+ channels underlying resting Ga; 2) parallels between the Ba2+ and TEA+ sensitivities of Ga(V) and maxi K+ channels support a role for these channels in Ga(V); and 3) quinine has multiple effects on K(+)-conductive pathways in gallbladder epithelium, which are only partially explained by block of apical membrane maxi K+ channels.

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