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M A Rogawski

Publications and source records attributed to M A Rogawski.

At least 91 records · Page 5Linked to original sources
PubMed1991

Glyburide-sensitive K+ channels in cultured rat hippocampal neurons: activation by cromakalim and energy-depleting conditions.

Previous studies in our laboratory have shown that cromakalim activates a tetraethylammonium-sensitive K+ current in cultured embryonic rat hippocampal neurons. This phenomenon was further characterized using whole-cell voltage-clamp and single-channel recording techniques. Glyburide (1-25 microM), an antagonist of ATP-sensitive K+ channels, produced a concentration-dependent depression of the cromakalim-activated current. In contrast, charybdotoxin (100 nM), an antagonist of some Ca(2+)-dependent and other K+ channels, not only failed to block the effect of cromakalim but actually produced a moderate enhancement of the cromakalim-activated K+ current. Neither glyburide nor charybdotoxin affected resting or voltage-activated K+ currents in the absence of cromakalim. Exposure of the cells to energy-depleting conditions (0.24 micrograms/ml oligomycin and 10 mM 2-deoxy-D-glucose) also activated an outward current. Single-channel recordings in the cell-attached configuration showed that cromakalim (100 microM) stimulated the opening of flickery single channels having a unitary conductance of approximately 26 pS and a prolonged burst duration (mean open time, approximately 131 msec); similar channel openings were observed in patches from cells exposed to energy-depleting conditions. In patches containing a single K+ channel, the open probability in the presence of cromakalim was approximately 0.6 and in the presence of energy-depleting conditions was approximately 0.8; in the absence of either of these treatments, channel openings were not observed. Glyburide produced a reversible inhibition of the channels activated by cromakalim and energy-depleting conditions. These data provide additional support for the existence of ATP-sensitive K+ channels in central neurons and indicate that the K+ channels whose opening is stimulated by cromakalim are likely to be of the ATP-sensitive type.

Adenosine Triphosphate↗
PubMed1991

Anticonvulsant activity of the low-affinity uncompetitive N-methyl-D- aspartate antagonist (+-)-5-aminocarbonyl-10,11-dihydro-5H- dibenzo[a,d]cyclohepten-5,10-imine (ADCI): comparison with the structural analogs dizocilpine (MK-801) and carbamazepine.

(+-)-5-Aminocarbonyl-10,11-dihydro-5H-dibenzo[a,d] [a,d]cyclohepten-5,10-imine (ADCI), a tricyclic compound structurally related to dizocilpine (MK-801) and carbamazepine, was a potent anticonvulsant in the mouse maximal electroshock seizure test when administered i.p. (ED50, 8.9 mg/kg) or p.o. (ED50, 23.5 mg/kg), but failed to cause motor impairment except at substantially higher doses (TD50 values, 49.2 mg/kg i.p. and 293 mg/kg p.o.). ADCI was also protective against chemically induced seizures in mice, including those produced by 4-aminopyridine (ED50, 7.1 mg/kg s.c.) and pentylenetetrazol (ED50, 37.4 mg/kg s.c.). In addition, ADCI antagonized the behavioral effects and lethality of s.c. administered N-methyl-D-aspartate (NMDA: ED50, 15.2 mg/kg), but was a weaker antagonist of kainate-induced clonic seizures (ED50, 33.0 mg/kg), indicating that the drug is a selective functional NMDA antagonist. In common with other NMDA antagonists, ADCI retarded the development of amygdaloid kindled seizures in rats, but failed to attenuate the afterdischarge duration in fully kindled animals. Whole cell voltage clamp recordings from cultured hippocampal neurons demonstrated that ADCI selectively blocks inward current responses to NMDA in a use-dependent fashion without affecting responses to kainate or quisqualate, indicating that ADCI is a selective open channel (uncompetitive) blocker of the NMDA receptor-ionophore complex. ADCI blocked NMDA-evoked inward current responses with a potency (IC50, 14 microM) similar to that with which it displaces [3H]-1-[1-(2-thienyl)-cyclohexyl]piperidine from binding to NMDA receptor channels in rat brain homogenates (IC50, 11.3 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1990

Synthesis and anticonvulsant activity of 1-phenylcyclohexylamine analogues.

Thirty-eight analogues of 1-phenylcyclohexylamine (PCA), a phencyclidine (PCP) derivative, were examined for their activities in the mouse maximal electroshock (MES) seizure test and in a motor-toxicity assay. In addition, we determined the binding affinities of the compounds for PCP acceptor sites in rat brain membranes labeled with [3H]-1-[1-(2-thienyl)cyclohexyl]piperidine. Many of the analogues were protective against MES seizures (ED50s of 5-41 mg/kg, ip) and all of these compounds caused motor toxicity. The potencies in the motor toxicity and MES seizure tests showed a moderate correlation with the affinities for PCP sites. Several analogues exhibited a greater separation of potencies in the motor toxicity and MES seizure tests than did the parent compound PCA. These were obtained by (i) 3-methylation of the cyclohexyl ring trans to the phenyl ring, (ii) methoxylation at the ortho position on the phenyl ring, and (iii) contraction of the cyclohexane ring to form the corresponding cyclopentane.

Animals↗
PubMed1989

BRL 34915 (cromakalim) enhances voltage-dependent K+ current in cultured rat hippocampal neurons.

The whole cell voltage-clamp recording technique was used to study the effects of the benzopyran antihypertensive agent BRL 34915 on voltage-dependent outward currents in cultured rat hippocampal neurons. Extracellular perfusion with BRL 34915 (10-500 microM) produced a dose-dependent increase in the sustained (minimally inactivating) voltage-dependent outward current without altering the transient outward current (IA) or producing a change in the resting current at -60 mV. One-half maximal facilitation of the sustained outward current occurred at 40 microM and maximal facilitation (59%) at 100 microM. The increase in outward current occurred at all potentials where hippocampal neurons exhibited outward rectification (greater than -30 mV). The effect of BRL 34915 was slow to develop (requiring as long as 5-15 min to achieve maximal effect) and persisted for at least 10-15 min after cessation of the drug superfusion. Like the sustained outward current recorded under control conditions, the outward current augmented by BRL 34915 was inhibited by the K+ channel blocker tetraethylammonium (20 mM). These results indicate that BRL 34915 can enhance the activity of sustained voltage-dependent K+ channels in mammalian CNS neurons.

Animals↗
PubMed1989

T-type calcium channels mediate the transition between tonic and phasic firing in thalamic neurons.

Thalamic neurons undergo a shift from tonic to phasic (burst) firing upon hyperpolarization. This state transition results from deinactivation of a regenerative depolarizing event referred to as the low-threshold spike. Isolated adult guinea pig thalamic (dorsal lateral geniculate) neurons exhibited low-threshold spikes that could be blocked by low concentrations of nickel but were unaffected by the dihydropyridine nimodipine. Whole-cell voltage-clamp recordings from these cells demonstrated a low-threshold, rapidly inactivating (T) Ca2+ current that manifested similar voltage dependency and time course as the low-threshold spike. Like low-threshold spikes, the T-type Ca2+ current was eliminated by nickel but was unaffected by nimodipine. In thalamic neurons, T-type Ca2+ channels underlie the low-threshold spike and, therefore, play a critical role in regulating the firing pattern of these cells.

Animals↗
PubMed1989

Cycloleucine blocks NMDA responses in cultured hippocampal neurones under voltage clamp: antagonism at the strychnine-insensitive glycine receptor.

1. Radioligand binding studies have demonstrated that the neutral amino acid cycloleucine may act as a competitive antagonist at the glycine modulatory site on the N-methyl-D-aspartate (NMDA) receptor complex. In the present study, we examined the effects of cycloleucine on NMDA-evoked inward current responses in dissociated hippocampal neuronal cultures using the whole cell voltage-clamp technique. 2. In the presence of 1 microM glycine, cycloleucine caused a reversible, dose-dependent inhibition of NMDA responses with an IC50 of 24 microM. An increase in glycine to 100 microM resulted in a shift to the right of the cycloleucine concentration-effect curve (IC50, 1.4 mM). However, with cycloleucine concentrations less than or equal to 100 microM, a fraction of the block could not be overcome by glycine even at concentrations as high as 1 mM. 3. The cycloleucine block was unaffected by shifts in the holding potential (-60 to +60 mV), and there was no effect of cycloleucine on the reversal potential of the NMDA-evoked current. 4. Cycloleucine failed to effect kainic acid- and quisqualic acid-evoked currents at concentrations which inhibited NMDA responses. 5. We conclude that cycloleucine is a potent and selective antagonist of NMDA-receptor mediated responses. Although this effect occurs in part via competitive antagonism at the glycine modulatory site, the cycloleucine block cannot be completely reversed by glycine indicating an interaction with an additional site on the receptor-channel complex.

Amino Acids↗
PubMed1989

Interaction of phencyclidine with voltage-dependent potassium channels in cultured rat hippocampal neurons: comparison with block of the NMDA receptor-ionophore complex.

Whole-cell voltage-clamp recording techniques were used to investigate the blockade of voltage-dependent K+ channels by phencyclidine (PCP) in cultured rat hippocampal neurons. All recordings were carried out in the presence of tetrodotoxin (1-2 microM) to eliminate Na+ currents. Step depolarization from a holding potential of -40 mV activated a slowly rising, minimally inactivating K+ current (IK). PCP (0.5-1000 microM) caused a reduction in the maximum conductance of IK [IC50(+30 mV), 22 microM] without altering its voltage dependency. The PCP block of IK diminished at depolarized potentials. Analysis according to the scheme of Woodhull (1973) suggested that block occurs via binding to an acceptor site (presumably within the channel pore) that senses 40-50% of the transmembrane electrostatic field. PCP had no effect on the kinetic properties of IK and the block failed to show use dependency, suggesting that PCP may bind to the IK channel via a hydrophobic mechanism not requiring open channels. For comparison, we also investigated the effect of PCP on the transient K+ current, IA, activated by step depolarization following a 200 msec prepulse to -90 mV (20 mM tetraethylammonium was present in the bathing solution to reduce IK). In contrast to the potent blocking action of PCP on IK, the drug only affected IA at high concentrations [IC50(+30 mV), 224 microM]. At concentrations causing substantial block (300-500 microM), PCP produced an acceleration in the IA inactivation rate, and, for brief (5-6 msec) depolarizing steps, the suppression of IA was use dependent. These observations suggest that PCP block of IA requires open channels. PCP reduced inward current responses induced by the excitatory amino acid agonist N-methyl-D-aspartate (NMDA) at substantially lower concentrations than those required for its effects on K+ channels [IC50(-60 mV), 0.45 microM]. The PCP-like dioxadrol stereoisomer dexoxadrol (10 microM) blocked NMDA-evoked inward current responses, while its behaviorally inactive enantiomer levoxadrol did not. Dexoxadrol and levoxadrol also blocked IK in a stereoselective fashion (IC50's, 73 and 260 microM, respectively), whereas the sigma ligands (+)- and (-)-SKF 10,047 and (+)-3-[3-hydroxyphenyl]-N-(1-propyl)piperidine [(+)-3-PPP] had little effect on the current (IC50's, greater than 300-500 microM). We conclude that PCP causes a selective, voltage-dependent block of IK in hippocampal neurons via a PCP- and not a sigma-type acceptor site.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Anticonvulsant activities of 1-phenylcyclohexylamine and its conformationally restricted analog 1,1-pentamethylenetetrahydroisoquinoline.

1-Phenylcyclohexylamine (PCA), an analog of phenyclidine (PCP) in which the piperidine ring is replaced by a primary amino group, and its conformationally restricted analog 1,1-pentamethylenetetrahydroisoquinoline (PM-THIQ) were potent anticonvulsants in the mouse maximal electroshock (MES) seizure test (ED50 values, 7.0 and 14.3 mg/kg, respectively). At higher doses, the drugs caused motor impairment (TD50 values, 16.3 and 43.0 mg/kg) and blocked the behavioral effects and lethality of i.p. injected N-methyl-D-aspartate (NMDA) (ED50 values, 36.3 and 127 mg/kg). The separation in potencies in the MES seizure and motor toxicity tests of PCA and PM-THIQ contrasts with PCP which was equally potent in both tests. Several compounds that were structurally related to PM-THIQ (N-ethyl-PCA, 2-methyl-PCA, N-methyl-PM-THIQ, tetrahydroisoquinoline and benzylamine) also blocked MES seizures and caused motor impairment, but failed to show as great a separation between MES anticonvulsant activity and motor toxicity. None of the compounds protected against seizures induced by the chemoconvulsant pentylenetetrazol at doses that lacked motor toxicity. The drugs were also evaluated for their ability to displace [3H]-1-[1-(2-thienyl)-cyclohexyl]piperidine from binding to high affinity acceptor sites (presumably on NMDA receptor-coupled channels) in rat brain homogenates. The rank order of potencies in the binding assay was similar to that in the behavioral tests, except for 2-methyl-PCA which was behaviorally more potent than expected.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Aminopyridines enhance opening of calcium-activated potassium channels in GH3 anterior pituitary cells.

The effects of aminopyridine analogs on Ca2+-activated K+ channels in GH3 clonal anterior pituitary cells were studied using whole-cell voltage-clamp and single-channel recording techniques. Step depolarization from a holding potential of -50 mV activated a noninactivating, tetraethylammonium- and Cd2+-sensitive outward current. Tail current analysis indicated that this sustained outward current is carried predominantly by K+ ions. Extracellular perfusion with 4-aminopyridine and 3,4-diaminopyridine (0.05-5 mM) caused a dose-dependent enhancement of the outward current by up to 100 and 170%, respectively. This effect typically occurred with prolonged depolarizations of greater than 1-2 sec. Patch-clamp recordings in the cell-attached configuration demonstrated that 4-aminopyridine (2 mM) promotes the activity of a large-conductance (150-175 pS; 50-135 mM external K+), tetraethylammonium-sensitive, Ca2+-activated K+ channel; the drug had no effect on these channels in excised patches. These results indicate that aminopyridines enhance the opening of Ca2+-activated K+ channels in GH3 cells. Several lines of evidence suggest that this effect may occur indirectly, possibly as a result of an increase in the effective intracellular free Ca2+ level.

Aminopyridines↗
PubMed1988

Phencyclidine selectively blocks the sustained voltage-dependent potassium conductance in PC12 cells.

We investigated the effects of phencyclidine (PCP), a psychotomimetic dissociative anesthetic, and several related drugs on voltage-dependent K+ currents in PC12 cells, a neuron-like clonal cell line derived from a rat pheochromocytoma. Whole-cell voltage clamp recordings demonstrated two kinetically distinct voltage-dependent outward (K+) current components in these cells: a rapidly activating and inactivating component, IA, that was selectively eliminated by 4-aminopyridine (2 mM) and a slowly activating, minimally inactivating (sustained) component, IK, that was specifically blocked by tetraethylammonium (20 mM). PCP (1-100 microM) produced a dose-dependent blockade of both IK and IA, however, at low doses the drug selectively reduced IK with little effect on IA; the IC50s for blockade of IK and IA were 4 and 25 microM, respectively. The blockade of IK was voltage-dependent so that the degree of block decreased with increasing depolarization, indicating that the blocking mechanism is likely one in which the positively charged PCP molecule is drawn into the channel pore. Several PCP related drugs also suppressed IK. Thienyl-PCP (TCP), a drug that is behaviorally more potent than PCP, partially blocked IK at low doses (31% at 1 microM), but even at high doses (25 microM) the degree of block was never as great as that produced by PCP. The optically active PCP congeners (+)-PCMP (1-(1-phenylcyclohexyl)-3-methyl-piperidine) and dexoxadrol were also potent blockers of IK. However, in contrast to the stereospecificity these compounds demonstrate in binding to high-affinity PCP receptors and in eliciting PCP-like behavioral responses, their enantiomers (-)-PCMP and levoxadrol showed similar potencies as the parent compounds in blocking IK. These results demonstrate that PCP and related drugs are powerful, selective blockers of IK in PC12 cells. The structure-activity studies indicate that this effect occurs at a site that is pharmacologically distinct from the behaviorally relevant PCP receptor. Blockade of K+ channels is unlikely to be responsible for the psychotomimetic or anti-convulsant properties of PCP, but could account for the convulsant potential of the drug.

Anesthetics↗
PubMed1988

Phencyclidine at low concentrations selectively blocks the sustained but not the transient voltage-dependent potassium current in cultured hippocampal neurons.

We studied the effects of phencyclidine (PCP) on voltage-dependent K+ currents in cultured embryonic rat hippocampal neurons. Whole cell voltage-clamp recordings were made in the presence of tetrodotoxin to block Na+ current. Depolarizing voltage steps activated two outward current components: (i) a rapidly activating and inactivating ('transient') component, IA, and (ii) a slowly activating, minimally inactivating ('sustained'), component, IK. At low concentrations (less than 50-100 microM), PCP produced a selective, reversible blockade of IK with minimal effect on IA; however, at higher concentrations both currents were suppressed. The IC50's for blockade of IK and IA were 36 and 310 microM, respectively.

Animals↗
PubMed1988

Transient outward current (IA) in clonal anterior pituitary cells: blockade by aminopyridine analogs.

Whole cell voltage-clamp recordings from GH3 cells, a clonal cell line derived from a rat anterior pituitary tumor, demonstrated a rapidly activating and inactivating ("transient") voltage-dependent outward current. This current, referred to as IA, was elicited by step depolarization from holding potentials negative to -50 mV, showed strong outward rectification at potentials positive to -30 mV, and exhibited steady state inactivation with V 1/2 near -64 mV. The current rose to a peak within less than 10-20 ms following depolarization and decayed in two exponential phases, IAf and IAs, with time constants of 30-50 and 500-700 ms, respectively. Both IA components exhibited similar voltage dependencies for activation and inactivation. Aminopyridines (2 mumol/1-5 mmol/l) produced a dose dependent, reversible blockade of IA (70% inhibition at 0.5 to 2 mmol/l) with the following rank order of potencies: 4-aminopyridine greater than 3,4-diaminopyridine = 3-aminopyridine greater than 2-aminopyridine. These drugs reduced the peak conductance of IA, and produced complex effects on its time-dependent decay. With submaximal degrees of block, there was an increase in the inactivation rate, suggesting that open channels are preferentially blocked by the drugs. It is concluded that GH3 pituitary cells possess an aminopyridine-sensitive transient outward current comparable to the A-current in neural cells. However, this cell line is unusual in that it expresses both rapidly and slowly decaying A-current components.

Aminopyridines↗
PubMed1988

A function for REM sleep: regulation of noradrenergic receptor sensitivity.

We hypothesize that REM sleep serves to upregulate and/or prevent downregulation of brain norepinephrine (NE) receptors. This hypothesis is based on the following observations: (1) NE neurons of the locus coeruleus (LC) are tonically active in waking and non-REM sleep, but the entire population of LC NE neurons is inactive during REM sleep. (2) Continuous presence of NE or adrenoceptor agonists downregulates NE receptors, while a reduction in NE availability upregulates these receptors. (3) The effects of REM sleep deprivation are similar to those of NE receptor downregulation. Recent biochemical studies of NE receptor sensitivity provide strong experimental support for this hypothesis. The functional consequence of enhanced NE receptor 'tone' brought about by REM sleep would be improved signal processing in diverse brain systems, thus endowing the organism with a selective advantage. This hypothesis makes a number of specific predictions which can be tested with currently available techniques, and suggests new ways of understanding the evolution and postnatal development of REM sleep.

Animals↗
PubMed1988

Vasopressin enhances a calcium current in human ACTH-secreting pituitary adenoma cells.

Arginine vasopressin (AVP) is a potent secretagogue for adrenocorticotropin (ACTH) release from normal corticotropes and from ACTH-secreting pituitary adenoma cells. To explore the mechanism underlying this action, we investigated the effects of AVP on Ca2+-dependent action potentials and Ca2+ currents in cultured human ACTH-containing pituitary tumor cells (hACTH adenoma cells). Pituitary adenoma fragments removed at surgery from two patients with Cushing's disease were dispersed, and the isolated cells were grown in monolayer culture. Most of the cells showed ACTH immunoreactivity that persisted even after as much as 2 months in culture. Current clamp and voltage clamp recordings were carried out using the patch-clamp technique in the whole cell configuration. AVP produced an increase in the amplitude and duration of action potentials in these cells, and substantially enhanced the transient after-hyperpolarization after each spike. Under voltage the transient after-hyperpolarization after each spike. Under voltage clamp, hACTH adenoma cells showed two Ca2+ current components: a low-threshold, rapidly inactivating (T-type) current; and a higher threshold, slowly inactivating (L-type) current. AVP markedly increased the amplitude of the L-type current without affecting the T-type current. These data suggest that AVP may enhance Ca2+ entry associated with action potentials by potentiating the activity of L-type Ca2+ channels. The resulting rise in cytosolic free Ca2+ may be a key link in the process by which AVP stimulates ACTH release in the pituitary.

Action Potentials↗
PubMed1988

A slow calcium-dependent chloride conductance in clonal anterior pituitary cells.

1. Whole cell voltage-clamp recordings were made from GH3 cells, a clonal cell line initially derived from a rat anterior pituitary tumor, using patch electrodes filled with CsCl or N-methylglucamine chloride (NMG Cl). The bathing medium contained tetraethylammonium chloride (TEA; 20 mM) and NaCl (120 mM) or NMG Cl (140 mM). These conditions resulted in substantial blockade of outward currents. 2. Depolarizing voltage steps from a holding potential of -50 mV activated transient (T-type) and sustained (L-type) inward Ca2+ currents. In addition, prolonged depolarization (greater than 1 s) invariably elicited a slowly activating inward current that persisted with maintained depolarization, and deactivated slowly on repolarization, resulting in a prominent inward tail current. 3. This tail current could be recorded under conditions where Ca2+ and Cl- were the only membrane-permeant ions (symmetrical NMG Cl). The tail current nulled near 0 mV with symmetrical Cl- and showed a negative reversal potential with nominally Cl--free internal solution. Ba2+ substituted for Ca2+ as a carrier of inward current, but no tail current was expressed. These observations indicate that Cl- is the charge carrier of the slow inward tail current. 4. The voltage dependence for activation of the slow tail current was U-shaped with a peak at approximately -10 mV. This closely paralleled the voltage dependency of the Ca2+ currents. Recordings with 5 mM internal ethylene glycol-bis(beta-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) to buffer intracellular Ca2+ to low nM levels exhibited slow inward tail currents that were of lower peak amplitude than with the usual 1.1 mM EGTA-containing pipette solution, but the kinetics of the currents were similar in both cases. In addition, the slow tail current was eliminated on superfusion with the Ca2+ channel blocker Cd2+ or with Ca2+-free medium. These results demonstrate that the current is dependent on Ca2+ influx; it is, therefore, referred to as ICl(Ca). 5. Activation of ICl(Ca) required depolarization of at least 1 s. More prolonged depolarizations activated progressively greater current, to a maximum with 6-s depolarization. In most cases, the decay of the tail current was described by a single exponential function with time constant approximately 0.8-0.9 s within the potential range -80 to -30 mV. At more depolarized potentials the decay was slower (increasing e-fold/20-mV change in membrane potential). 6. In a high proportion of cells, ICl(Ca) rapidly diminished in amplitude on repeated activation. This "rundown" occurred more rapidly than the rundown of the Ca2+ currents.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Tetrahydroaminoacridine blocks voltage-dependent ion channels in hippocampal neurons.

Tetrahydroaminoacridine (THA) is a centrally active anticholinesterase that may produce functional improvement in patients with Alzheimer's disease. Because of its structural similarity to the potassium channel (A-current) blocking drug 4-aminopyridine (4-AP), it has been speculated that some of the therapeutic benefit of THA might result from inhibition of potassium currents. In the present study, THA produced a dose-dependent, reversible block of the A-current in cultured hippocampal neurons (IC50, 30 microM). However, at similar concentrations it also inhibited other voltage-dependent currents.

Aminoacridines↗