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PubMed1988

Expression of membrane currents in rat neocortical neurons in serum-free culture. II. Outward currents.

The timing of expression and properties of outward membrane currents in cultured neocortical pyramidal-shaped neurons have been investigated using the gigaseal whole-cell voltage clamp and single-channel recording techniques. Dissociated primary cultures of synchronized (same cell cycle), growth arrested (G1 phase) and birth-dated cells from fetal rat (E18) were maintained in a serum-free medium. The earliest appearing membrane current in the soma is a voltage-dependent outward current carried by K+. The current consists of two components, one rapidly rising component, resembling those associated with the transient outward current (IA) and the other similar to the delayed rectifier current (IK). The ratio between the peak IA and IK was about 0.3 at all membrane voltages. The magnitude of both IA and IK increased with time in culture but the ratio remained unchanged. Direct measurements of unitary currents showed the presence of two voltage-activated outward conductances, 32 pS and 120 pS. The small conductance channel was sparse. The large conductance channel is K+-selective and was sensitive to both voltage and internal Ca2+.

Animals↗
PubMed1994

Voltage-dependent ion channels in glial cells.

Glial cells, although non-excitable, express a wealth of voltage-activated ion channels that are typically characteristic of excitable cells. Since these channels are also observed in acutely isolated cells and in brain slices, they have to be considered functional in the intact brain. Numerous studies over the past 10 years have yielded detailed characterizations of glial channels permitting comparison of their properties to those of their neuronal counterparts. While for the most part such comparisons have demonstrated a high degree of similarity, they also provide evidence for the expression of some uniquely glial ion channels. An increasing number of studies indicate that the expression of "glial" channels is influenced by the cells' microenvironment. For example, the presence of neurons can induce or inhibit (depending on the preparation and type of channel studied) the expression of glial ion channels. Like ion channels in excitable cells, glial channels can be functionally regulated by activation of second-messenger pathways, allowing for short-term modulation of their membrane properties. Although the extent to which most of the characterized ion channels are involved in glial function is presently unclear, a growing body of data suggests that certain channels play an active role in glial function. Thus inwardly rectifying K+ channels in concert with delayed rectifying K+ channels are thought to be involved in the removal and redistribution of excess K+ in the brain, a process referred to as "spatial buffering". Glial K+ channels may also be crucial in modulating glial proliferation. Cl- channels and stretch-activated cation channels are believed to be involved in volume regulation. Na+ channels appear to be important in fueling the glial Na+/K(+)-pump, and Ca2+ channels are likely involved in numerous cellular events in which intracellular Ca2+ is a critical second messenger.

Animals↗
PubMed1997

Ionic basis of learning-correlated excitability changes in Hermissenda type A photoreceptors.

Repeated pairings of light and rotation (conditioning) result in persistent changes in excitability of Hermissenda type B and A photoreceptors, which are correlated with pairing-specific reductions in phototactic behavior. Although considerable attention has been devoted to characterization of conditioning-produced neurophysiological changes that occur in type B cells, less information is available concerning the changes produced in type A cells. Here we recorded from identified, synaptically isolated lateral and medial type A photoreceptors from conditioned, random-control, or untrained animals on retention days following conditioning. Type A photoreceptors from conditioned animals responded to light with a receptor potential that was significantly smaller than those of random-control or untrained animals, which did not differ. The phototactic suppression and type A cell light response magnitudes were negatively correlated for individual conditioned animals. Animals exhibiting strong phototactic suppression also showed small light responses. Expression of the training-associated light response difference was a calcium-dependent phenomenon: reducing extracellular calcium to < 1 microM enhanced the generator potential of A cells, regardless of conditioning history, and greatly reduced the differences in generator potential amplitude attributable to training. Voltage-clamp studies revealed that conditioning resulted in a two- to threefold increase in the amplitude of a voltage-dependent, sustained outward K+ current (I(Delayed)). I(Delayed) magnitudes were positively correlated with phototactic suppression for individual conditioned animals: type A cells of animals exhibiting strong phototactic suppression expressed large values of I(Delayed). I(Delayed) is a composite current, consisting of at least three separable components: 1) residual A current (I(A)); 2) slow, tetraethylammonium-sensitive calcium-activated K+ current (I(K-Ca)); and 3) a delayed-rectifier-type, voltage-dependent K+ current (I(K,v)). Analysis of these currents failed to reveal significant training-associated changes in I(A) or I(K-Ca). But I(K,v) was enhanced by approximately 60-150% in both lateral and medial cells and thus contributes to the conditioning-associated increase in I(Delayed).

Analysis of Variance↗
PubMed2003

Inhibition by fluoroquinolones of K(+) currents in rat dissociated hippocampal neurons.

The effects of four fluoroquinolones (sparfloxacin, fleroxacin, ofloxacin and levofloxacin) on K(+) currents were investigated in pyramidal neurons acutely isolated from rat hippocampus, to evaluate their relative potencies for inhibiting these channels. Using patch-clamp electrophysiological techniques, we found that all four compounds inhibited the delayed rectifier K(+) current (I(K)), but with different potencies. Sparfloxacin was the most potent compound, displaying an IC(50) value of 6.44 x 10(-4) M, followed by fleroxacin, ofloxacin and levofloxacin, their IC(50) values being 7.09 x 10(-3), 8.42 x 10(-3) and 1.10 x 10(-2) M, respectively. In contrast, the fast transient K(+) current (I(A)) was blocked only by sparfloxacin (IC(50)=2.86 x 10(-3) M) and fleroxacin (IC(50)=4.38 x 10(-3) M), but not by ofloxacin and levofloxacin even at concentrations up to 1 mM. The K(+) current inhibition was reversible after washout of the compounds. Further study is needed to clarify the possible involvement of this novel action in the adverse effects of fluoroquinolones in the central nervous system (CNS).

Animals↗
PubMedDate not supplied

[Comparative study of electrophysiological mechanisms of anti-arrhythmia III class agents, cardiocyclide, nibentan, and sotalol during experimental myocardial infarction and sympathetic stimulation].

Electrophysiological mechanisms of the action of cardiocyclide, nibentan, and sotalol--antiarrhythmic agents of class III--was studied in dogs with experimental myocardial infarction induced by a two-step occlusion of the coronary artery. Cardiocyclide exhibited the properties typical of the class III antiarrhythmics by prolonging the ventricular repolarization and increasing the effective refractory periods in the atrium and ventricles. The degree of manifestation of these antiarrhythmic effects of cardiocyclide is independent of the induced heart rate, which is related to the ability of this drug to block the slow activation component (IKs) of the delayed rectified potassium current. Nibentan elongates the QT interval and increases the effective atrial and ventricular refractory periods, but the effect was dependent of the stimulation frequency. Sotalol, which also exhibited the properties of a class III antiarrhythmogen possessing beta-blocking activity, produced more pronounced inhibiting action upon the sinus node function and conduction (in comparison with the analogous effects of cardiocyclide). This is probably related to the ability of sotalol to block the cardiac adrenoreceptors. The effect of sotalol is also frequency-dependent, which is related to the blocking of rapid activating component (IKr) of) of the delayed rectified potassium current. On the background of isoproterenol infusion, cardiocyclide completely retained the electrophysiological and antiarrhythmic effects. The efficacy of nibentan and sotalol with respect to the repolarization and refractoriness significantly decrease under the conditions of sympathetic nervous system activation. The ability of sotalol to suppress the sinus node function and conduction on the background of isoproterenol infusion is retained.

Adrenergic beta-Agonists↗
PubMed1997

The ionic mechanisms of early after depolarization in mouse ventricular myocytes: the role of IK1.

The occurrence of early after depolarization (EAD) in single mouse ventricular myocytes was observed and its ionic mechanisms were studied using the patch clamp technique. Under treatment with perfusion of Tyrode's solution containing 3 mM KCl and 3 mM CsCl, 3/6 cases exhibited EAD, while with 3 mM KCl or 3 mM CsCl alone, EAD was not induced. The background steady-state current-voltage (I-V) curves of the myocytes showed no negative slope, i.e., the slope in the range of 50 mV positive to the reversal potential was virtually flat and stayed at a low current level. Under perfusion of 3 mM KCl and 3 mM CsCl, the outward current in the above region decreased nearly to 0: in the myocytes which exhibited EAD, a net inward current (crossover) was displayed in the same region, which was abolished by 10 microM TTX and 10 microM nifedipine. The results of whole-cell inward rectifier current I-V curves were similar to the above background steady-state I-V curves. In mouse ventricular myocytes, transient outward current was very strong with a peak current density of 63 +/- 19 pA/pF, whereas low K+ and Cs+ had no significant effect. 11/30 cases showed obvious delayed rectifier current, but the tail current recorded by envelope method was relatively weak (1.19 +/- 0.35 pA/pF) and insensitive to CsCl or changing of the KCl concentration. The results suggest that under treatment with low K+ and Cs+, the inhibition of inward rectifier current is the basis of the formation of second plateau, while Na and Ca currents contribute to the generation of triggered bursts.

Animals↗
PubMed1987

Potassium currents evoked by brief depolarizations in bull-frog sympathetic ganglion cells.

1. Sympathetic neurones of the bull-frog Rana catesbeiana were subjected to a two-electrode voltage-clamp technique in order to investigate the K+ currents which can be elicited by action potentials or similar brief depolarizations. 2. Four separate K+ currents were observed (IC, IK, IAHP and IM). These could be separated on the basis of voltage sensitivity, Ca2+ dependence and deactivation kinetics. 3. Two of these currents, which were clearly activated by an action potential, were Ca2+ dependent. A voltage- and TEA (tetraethylammonium)-sensitive K+ current, IC, was activated within the first 1-2 ms of a depolarizing command. This current decayed on average with a time constant of 2.4 ms at -40 mV. The maximal conductance was outside the range which could be adequately voltage clamped but, as much as 2 muS could be activated by brief (2-3 ms) commands. Activation of IC during an action potential accounts for the Ca2+ dependence of the repolarization. IC did not exhibit a transient component. 4. A second Ca2+-dependent K+ current, IAHP, was also activated after as little as 1 ms depolarization but was not voltage sensitive and was much less sensitive to TEA. The current decayed with a time constant of around 150 ms at -40 mV. The maximal conductance was about 30 nS. 5. The voltage-sensitive delayed rectifying current, IK, made a contribution to the total K+ conductance of the cell similar to IC in magnitude; however, the current is not activated within the normal voltage range or time course of an action potential. The current decayed on average with a time constant of 21 ms at -40 mV. 6. IM, a muscarine- and voltage-sensitive current, is not activated to any significant degree by a single action potential. The data further imply that the rate of opening of the ion channels mediating IM is less voltage sensitive than the rate of closing. 7. Large changes in the K+ reversal potential occur following depolarizing commands which evoke large K+ currents. This is attributed to K+ accumulation within a restricted extracellular space. Extracellular K+ may double or even triple during a single action potential.

Action Potentials↗
PubMed1992

Effects of BRL 38227 on potassium currents in smooth muscle cells isolated from rabbit portal vein and human mesenteric artery.

1. Single smooth muscle cells were isolated from the rabbit portal vein and the human mesenteric artery and whole cell currents recorded at room temperature from either cell type by the whole cell voltage clamp technique. 2. In the rabbit portal vein cells addition of 10 microM BRL 38227 induced a quasi-instantaneous, voltage-insensitive and time-independent current which had a reversal potential of -75 mV under experimental conditions where the calculated EK was -83 mV. 3. Cells were held at 0 mV and BRL 38227 was added cumulatively to construct a dose-response relationship. BRL 38227 (0.03-10 microM) caused a dose-dependent outward shift in the holding current with an EC50 of 1.3 microM. 4. BRL 38227 (10 microM) had no effect on the delayed rectifier K+ current measured in the presence of 5 mM tetraethylammonium and no effect on the Ca(2+)-activated K+ current measured in the presence of 5 mM 4-aminopyridine. Similarly BRL 38227 had no effect on the Ca2+ current. 5. The BRL 38227-induced current was blocked by glibenclamide (10 microM) and phentolamine (100 microM), specific blockers of the ATP-sensitive K+ current in single cells. 6. In human isolated mesenteric artery cells, BRL 38227 (10 microM) induced a glibenclamide-sensitive current similar to, but smaller than, that observed in the rabbit portal vein. 7. We conclude that in these cells, BRL 38227 activates a potassium conductance which has the electrophysiological and pharmacological characteristics of ATP-sensitive K+ channels.

Animals↗
PubMed1991

Suppression of time-dependent outward current in guinea pig ventricular myocytes. Actions of quinidine and amiodarone.

Prolongation of cardiac action potentials may mediate some of the arrhythmia-suppressing and arrhythmia-aggravating actions of antiarrhythmic agents. In this study, suppression of time-dependent outward current by quinidine and amiodarone was assessed in guinea pig ventricular myocytes. The net time-dependent outward current contained at least two components: a slowly activating, La(3+)-resistant delayed rectifier current (IK) and a rapidly activating, La(3+)-sensitive current. Quinidine block of total time-dependent outward current during clamp steps to positive potentials was relieved as a function of time, whereas that induced by amiodarone was enhanced. In contrast, at negative potentials, suppression of current, whereas amiodarone reduced IK but not the La(3+)-sensitive current, suggesting that differential block of the two components of time-dependent current underlies the distinct effects of the two agents. In contrast to these disparate effects on total time-dependent outward current, steady-state reduction of IK by both drugs increased at positive voltages and saturated at approximately +40 mV; the voltage dependence of block by quinidine (17% per decade, +10 to +30 mV) was steeper than that by amiodarone (5% per decade, +10 to +20 mV). Block by quinidine was time dependent at negative potentials: on stepping from +50 to -30 mV, block initially increased very rapidly, and subsequent deactivation of IK was slowed. This effect was not seen with amiodarone. At -80 mV, quinidine block was relieved with a time constant of 40 +/- 15 msec (n = 4, twin-pulse protocol). The effects of quinidine on IK were compatible with neither a purely voltage-dependent model of quinidine binding nor a model incorporating both voltage- and state-dependent binding of quinidine to delayed rectifier channels having only one open state. The voltage- and time-dependent features of quinidine block were well described by a model in which quinidine has greater affinity for one of two open states of the channel. We conclude that the effects of quinidine and amiodarone on time-dependent outward current reflects block of multiple channels. Quinidine block of IK was far more voltage dependent than that produced by amiodarone, suggesting the drugs act by different mechanisms.

Action Potentials↗
PubMed1997

Electrophysiological actions of ryanodine on single rabbit sinoatrial nodal cells.

1. Effects of ryanodine on the action potentials and the ionic currents in spontaneously beating single rabbit sinoatrial (SA) nodal cells were examined using current-clamp and whole-cell voltage-clamp techniques. 2. Cumulative administrations of ryanodine (10(-8) to 10(-4) M) caused a negative chronotropic effect in a concentration-dependent manner; the effect was not modified by atropine (10(-7) M). At 10(-6) M, ryanodine increased the action potential amplitude and the maximum rate of depolarization, and prolonged the duration of action potentials, significantly. The maximum diastolic potential was unaffected. 3. No arrhythmia occurred in the presence of ryanodine (10(-6) M) alone, but addition of either caffeine (10 mM) or high Ca2+ (10.8 mM) elicited arrhythmias. The incidence increased with an increase in extracellular Ca2+ concentration. 4. Ryanodine, at 10(-6) M, enhanced the Ca2+ current but, at 10(-5) M, inhibited it. Ryanodine inhibited the delayed rectifier K+ current and the hyperpolarization-activated inward current in a concentration-dependent manner. 5. In addition, ryanodine actually elevated the cytosolic Ca2+ level in the SA nodal cells loaded with Ca(2+)-sensitive fluorescent dye (fura-2). 6. These results indicate that ryanodine modulates the ionic currents (presumably dependent on cellular Ca2+ concentration), suggesting similar pharmacological properties to caffeine.

Action Potentials↗
PubMed2006

MCP-1 enhances excitability of nociceptive neurons in chronically compressed dorsal root ganglia.

Previous experimental results from our laboratory demonstrated that monocyte chemoattractant protein-1 (MCP-1) depolarizes or increases the excitability of nociceptive neurons in the intact dorsal root ganglion (DRG) after a chronic compression of the DRG (CCD), an injury that upregulates neuronal expression of both MCP-1 and mRNA for its receptor CCR2. We presently explore the ionic mechanisms underlying the excitatory effects of MCP-1. MCP-1 (100 nM) was applied, after CCD, to acutely dissociated small DRG neurons with nociceptive properties. Under current clamp, the proportion of neurons depolarized was similar to that previously observed for CCD-treated neurons in the intact ganglion, although the magnitude of depolarization was greater. MCP-1 induced a decrease in rheobase by 44 +/- 10% and some cells became spontaneously active at resting potential. Action potential width at a voltage equal to 10% of the peak height was increased from 4.94 +/- 0.23 to 5.90 +/- 0.47 ms. In voltage clamp, MCP-1 induced an inward current in 27 of 50 neurons held at -60 mV, which increased with concentration over the range of 3 to 300 nM (EC(50) = 45 nM). The MCP-1-induced current was not voltage dependent and had an estimated reversal potential of -27 mV. In addition, MCP-1 inhibited a voltage-dependent, noninactivating outward current, presumably a delayed rectifier type K(+) conductance. We conclude that MCP-1 enhances excitability in CCD neurons by, at least, two mechanisms: 1) activation of a nonvoltage-dependent depolarizing current with characteristics similar to a nonselective cation conductance and 2) inhibition of a voltage-dependent outward current.

Action Potentials↗
PubMed1999

The effects of oxidizing and cysteine-reactive reagents on the inward rectifier potassium channels Kir2.3 and Kir1.1.

The inwardly rectifying potassium channel Kir2.3 possesses extracellular cysteine residues at positions 113, 140, and 145, as well as at position 79 near the outer membrane boundary. In this study, we have investigated the roles of these extracellular cysteine residues in mediating inhibition of the Kir2.3 channel by the cysteine-reactive reagents para-chloromercuribenzenesulphonate (PCMBS) and thimerosal, and the oxidizing agent hydrogen peroxide (H2O2). We have also compared the effects of these reagents with those on Kir1.1 channels (which do not possess cysteine residues equivalent to 140 and 79 in Kir2.3 channels). Mutant channels were made in which cysteine residues were mutated to serine by site-directed mutagenesis. Wild-type or mutant cRNA was injected into Xenopus oocytes and voltage-clamp recordings made 1-2 days later. Wild-type Kir2.3 currents were significantly inhibited by PCMBS, thimerosal and H2O2. Currents for mutants Kir2.3 C79S and C140S were also inhibited by PCMBS, thimerosal and H2O2. These mutations affected the time course of inhibition by all three reagents. For PCMBS, a slow component of inhibition was absent for the C79S mutation, and a fast component was absent for C140S. For the double mutation C79S/C140S, PCMBS no longer had any effect. For thimerosal, there was a slower time course for C140S, a faster time course for C79S, and a delayed onset for C79S/C140S. For H2O2, the main effect was a delayed onset for the double mutant. The reducing agent dithiothreitol (DTT) reversed the inhibition by both PCMBS and thimerosal of wild-type and mutant currents, but not the inhibition due to H2O2. Finally, wild-type Kir1.1 currents were not significantly inhibited by the applications of either PCMBS or thimerosal, while H2O2 produced small inhibition. The results taken together indicate that inhibition by the cysteine-reactive reagent PCMBS is mediated through cysteine residues 79 and 140 in Kir2.3 channels, with C79 mediating a slow component of inhibition and C140 a faster component, and that both residues are extracellularly exposed. The data indicate that these two cysteine residues are also main sites for inhibition by thimerosal and H2O2 but, unlike for PCMBS, an additional non-extracellular inhibitory site(s) must also be involved.

4-Chloromercuribenzenesulfonate↗
PubMed1994

Heterotetramer formation and charybdotoxin sensitivity of two K+ channels cloned from smooth muscle.

Delayed rectifier K+ channels are involved in the electrical activity of all excitable cells. The relationship between native K+ currents recorded from these cells and cloned K+ channel cDNAs has been difficult to ascertain partly because of contradictions in pharmacological characteristics between native and expressed currents. Through the study of the charybdotoxin (CTX) pharmacology of two cloned smooth muscle delayed rectifier K+ channels (cKv 1.2 and cKv1.5) expressed in oocytes, evidence for heterotetramer formation was obtained. We have shown that the presence of even a single CTX-insensitive subunit renders the heterotetrameric channel insensitive to CTX. The two K+ channel clones differ in an amino acid at the mouth of the pore region, which may be in a position to block the access of CTX to its binding site and hence determine CTX sensitivity of the heterotetrameric channel. These results may explain discrepancies reported between native and cloned smooth muscle K+ channels.

Amino Acid Sequence↗
PubMed1999

Investigation on SCH00013, a novel cardiotonic agent with Ca++ sensitizing action. 1st communication: phosphodiesterase III inhibitory effect and class III antiarrhythmic effect in guinea-pig heart.

In order to clarify the mechanism of action of 4,5-dihydro-6-[1-[2-hydroxy-2-(4-cyanophenyl)ethyl]-1,2,5,6- tetrahydropyrido-4-yl]pyridazin-3(2H)-one (SCH00013), a novel cardiotonic agent with Ca++ sensitizing action, its effects on contractile force, atrial rate and action potential, and on the activity of Na+, K(+)-ATPase and phosphodiesterase (PDE) I-IV were studied in the guinea-pig heart. SCH00013 exerted a positive inotropic effect (PIE) on isolated right ventricular papillary muscles in a concentration-dependent manner (EC50 = 9.2 mumol/l): the relative potency was milrinone > SCH00013 > vesnarinone. The PIE of SCH00013 was not influenced by propranolol, a beta-blocker, and SCH00013 did not affect the activity of cardiac Na+, K(+)-ATPase. The PIE of SCH00013 was partially inhibited by carbachol, a muscarinic receptor agonist, which implies a partial contribution of the cAMP-dependent mechanism to the PIE. SCH00013 inhibited the activity of PDE III selectively, but the potency was weak: the IC50 value was 64.9 mumol/l, which was 46 and 3.9 times less potent than those of milrinone and vesnarinone, respectively. SCH00013 and vesnarinone elicited a moderate decrease in the rate of beating of isolated right atria, while milrinone increased it. SCH00013 markedly prolonged the action potential duration and the effective refractory period with no change in the resting membrane potential and dV/dtmax, an indication that SCH00013 may suppress the activity of delayed rectifying K+ channels. These results indicate that SCH00013, that primarily acts as a Ca++ sensitizer, possesses a weak selective PDE III inhibitory effect. The potential positive chronotropic effect of SCH00013 due to PDE III inhibition may be offset by its effect on K+ channels.

Action Potentials↗
PubMed1995

Action potentials, ionic currents and cell water in guinea pig ventricular preparations exposed to dimethyl sulfoxide.

Superfusion of guinea pig papillary muscles with Tyrode's solution that contained 0.3% to 10% dimethyl sulfoxide (DMSO) caused a small hyperpolarization, a prolongation of the action potential (e.g., 4%, 15% and 33% prolongation with 1%, 5% and 10% DMSO, respectively) and a reduction (< or = 14%) in the maximal upstroke velocity (Vmax). Action potential prolongation was also induced by DMSO in muscles treated with the inorganic Ca++ channel blocker Co++ (5 mM) and in those depolarized with 24 mM K(+)-containing Tyrode's solution. In the latter case, there was no significant change in Vmax. In voltage-clamp experiments, superfusion of guinea pig ventricular myocytes with 0.1% to 10% DMSO solution had little effect on Ca++ and inward-rectifier K+ currents, moderately inhibited Cl- and Na+ currents, partially inhibited Na+ pump current and markedly depressed delayed-rectifier K+ current. The cell water shrinkages measured in muscles and myocytes superfused with DMSO solution appear to be only partially responsible for the solvent's effects. Other mechanisms that may be of greater importance in explaining the action of DMSO include direct block of channels by DMSO molecules and hindrance of channel hydration and opening related to osmotic stress.

Action Potentials↗
PubMed1993

Whole-cell recording of neuroblastoma x glioma cells during downregulation of a major substrate, 80K/MARCKS, of protein kinase C.

Differentiated neuroblastoma cells exhibit both the delayed rectifier potassium current (IK) and the M-current (IM). The present study was designed to determine the roles of protein kinase C (PKC) and of the calmodulin-binding protein 80K/MARCKS, a prominent substrate for PKC and possible regulator of these currents. Neuroblastoma x glioma (NG108-15) hybrid cells transfected with m1 muscarinic receptors were grown with 1% fetal bovine serum (FBS) without the prostaglandin E1 (PGE1) and isobutylmethylxanthine (IBMX) usually added in preparation for electrophysiological studies. Under these conditions, the usual pleomorphism was largely abolished, leaving two populations of small cells with stellate and spherically symmetrical geometries. Whole-cell patch clamping indicated that the two cell types had identical electrophysiological properties, displaying: IK, a small current through a "T-like" Ca2+ channel, and no M-current. Stimulation with carbachol shifted the distribution of cells to a more stellate morphology within 24 hr and later (after 48 hr) reduced the PKC substrate 80K/MARCKS by 22 +/- 7%. In contrast to the stimulation of IK observed with cardiac cells, PKC activation produced only a small inhibition of IK, which was independent of carbachol pretreatment. Thus, PKC and 80K/MARCKS can be dissociated from the regulation of IK in neuroblastoma cells.

Animals↗
PubMed2004

NGF-mediated sensitization of the excitability of rat sensory neurons is prevented by a blocking antibody to the p75 neurotrophin receptor.

Nerve growth factor (NGF) can play a causal role in the initiation of hyperalgesia. Recent work demonstrates that NGF can act directly on nociceptive sensory neurons to augment their sensitivity to a variety of stimuli. Based on the existing literature, it is not clear whether this sensitization is mediated by the high-affinity TrkA receptor or the low-affinity p75 neurotrophin receptor. We examined whether a blocking antibody to the p75 neurotrophin receptor can prevent the NGF-induced enhancement of excitability in capsaicin-sensitive small-diameter sensory neurons that have been isolated from the adult rat. In this report, pretreatment with the p75 blocking antibody completely prevents the NGF-induced increase in the number of action potentials evoked by a ramp of depolarizing current as well as the suppression of a delayed rectifier-type of potassium current(s) in these neurons. Although the sensitization by NGF was blocked, the antibody had no effect on the capacity of ceramide, a putative downstream signaling molecule, to either enhance the excitability or inhibit the potassium current. These results indicate that NGF can increase the excitability of nociceptive sensory neurons through activation of the p75 neurotrophin receptor and its consequent liberation of ceramide from neuronal sphingomyelins.

Action Potentials↗
PubMed2001

Effects of KRN2391 on ionic currents in rabbit femoral arterial myocytes.

The effects of KRN2391, an ATP-sensitive K+ channel opener (KCO) which also acts as a nitrate, on ionic membrane currents in rabbit femoral arterial myocytes were examined. Under whole-cell clamp conditions where cells were superfused with physiological salts solution containing 5.9 mM K+, KRN2391 elicited an outward current at a holding potential of -30 mV. KRN2391-induced current had a reversal potential of -78 mV and was abolished by glibenclamide (glib). KRN2391 was approximately 25 times more potent than nicorandil to activate an ATP-sensitive K+ current (I:(KATP)). On the other hand, 10 microM KRN2391 did not affect either voltage-dependent Ca(2+) or delayed rectifier K+ channel currents. In the inside-out patch configuration, KRN2391 activated 47 pS K+ channels in the presence of nucleotide diphosphates (NDPs) under the symmetrical 140 mM K+ conditions. Glib and intracellular ATP reversibly inhibited the activity of the 47 pS K+ channels. The 47 pS K+ channels activated by KRN2391 are similar in their conductance and other properties to NDP-sensitive K+ channels (K(NDP) channels) described in other smooth muscles and the cloned channels. KRN2391 is a potent activator of the 47 pS K+ channels and the activation can contribute to the KRN2391-induced vasodilation in arterial muscles.

Adenosine Diphosphate↗