Search PubMed⌕ Search

Biomedical subjects

K Dunlap

Publications and source records attributed to K Dunlap.

At least 55 records · Page 3Linked to original sources
PubMed1991

Interleukin-1 augments gamma-aminobutyric acidA receptor function in brain.

Interleukin-1 (IL-1), a cytokine involved in the acute phase reaction to injury and infection, has multiple effects in the central nervous system, including induction of fever and sleep and the release of several neuropeptides. We evaluated effects of IL-1 beta on inhibitory postsynaptic function at the gamma-aminobutyric acidA (GABAA) receptor. IL-1 (100 pg/ml to 10 ng/ml) augmented GABAA receptor function in cortical synaptic preparations. This effect of IL-1 was largely prevented by incubation with a specific IL-1 receptor antagonist. The related cytokines interleukin-6 and tumor necrosis factor did not augment GABA-dependent chloride transport. Similar enhancement of GABAA receptor function was observed in tissue prepared from mice previously injected intraperitoneally with IL-1 (1 microgram). Electrophysiological studies in cultured primary cortical neurons demonstrated that IL-1 enhanced the GABA-mediated increase in chloride permeability, whereas IL-1 alone produced no alterations in resting conductance. Behavioral studies indicated that IL-1 is similarly active in vivo; mice treated with IL-1 showed a decrease in open-field activity and an increase in the threshold for pentylenetetrazol-induced seizures. The interaction of IL-1 with GABAA receptors might account for the somnogenic and motor-depressant effects of this cytokine.

Animals↗
PubMed1989

Intercellular signaling as visualized by endogenous calcium-dependent bioluminescence.

Bioluminescence in the hydrozoan coelenterate Obelia results from calcium activation of a photoprotein contained in light-emitting cells (photocytes) scattered in the animal's endoderm. The influx of calcium into nonluminescent endodermal cells through conventional voltage-dependent calcium channels is required for the excitation-luminescence coupling. Our results suggest that the subsequent diffusion of this calcium, via gap junctions, into the neighboring photocytes triggers a localized luminescence response. Following intense stimulation, the local rise in calcium elicits a secondary wave of luminescence that is supported by a voltage-independent calcium permeability mechanism in the photocyte plasma membrane. These two mechanisms for elevating internal calcium in light-emitting cells can account for the spatial and temporal features of intracellular luminescence in Obelia.

Animals↗
PubMed1989

Specific inhibitors of protein kinase C block transmitter-induced modulation of sensory neuron calcium current.

Modulation of neuronal, voltage-dependent calcium current has been described for a number of transmitters and peptides, but the biochemical basis for this phenomenon has not been completely identified. In several cases protein kinase C (PKC) is thought to mediate transmitter inhibition of calcium current; however, a lack of specific PKC inhibitors has hampered a direct physiological test of this idea. We have used the whole-cell, tight-seal configuration of the patch-clamp technique to apply intracellularly two specific PKC inhibitors to the cell bodies of embryonic chick sensory neurons. Both inhibitors, a 17 kd protein purified from bovine brain and a synthetic 13 amino acid "pseudosubstrate" peptide, blocked inhibition of calcium current by either norepinephrine or an exogenously applied PKC activator. These results provide strong evidence that activation of PKC is a prerequisite for the modulation of sensory neuron calcium current by norepinephrine.

Animals↗
PubMed1989

G proteins couple alpha-adrenergic and GABAb receptors to inhibition of peptide secretion from peripheral sensory neurons.

Regulation of neuronal calcium channels by GTP-binding proteins (G proteins) is likely to be an important mechanism by which inhibitory transmitters influence excitation-secretion coupling in presynaptic nerve endings. Here, we report that in peripheral sensory neurons from embryonic chick dorsal root ganglia (DRG), the G protein-mediated inhibition of voltage-dependent calcium channels may best explain how norepinephrine (NE) and GABA inhibit the electrically evoked, calcium-dependent release of substance P (SP). As is the case for the previously reported inhibitory actions of these transmitters on DRG cell calcium channels, we demonstrate that NE and GABA inhibit peptide secretion through activation of alpha-adrenergic and GABAb receptors that are functionally coupled to pertussis toxin (PTX)-sensitive G proteins. Pretreatment of DRG cell cultures with PTX blocked the ability of NE and GABA to inhibit the release of SP, an action correlated with PTX-catalyzed ADP-ribosylation of membrane proteins with apparent molecular weight (Mr) of 40-41 kDa. Western immunoblot analysis of chick DRG cell membrane proteins using antisera directed against synthetic peptides corresponding to amino acid sequences predicted from cDNAs for PTX-sensitive G protein alpha subunits revealed a minimum of 2 Gi-like proteins (Mr 40 and 41 kDa) and a third Go-like protein (Mr 40 kD). Significantly, these findings implicate Gi- and/or Go-like GTP-binding proteins as mediators of presynaptic inhibition in peripheral sensory neurons.

Adenosine Diphosphate Ribose↗
PubMed1988

Characterization of the electrically evoked release of substance P from dorsal root ganglion neurons: methods and dihydropyridine sensitivity.

The mechanism by which dihydropyridines (DHPs) modulate the electrically evoked or KCI-induced release of substance P (SP) from embryonic chick dorsal root ganglion (DRG) neurons was investigated in the present study. The release of SP, as measured by radioimmunoassay (RIA), was characterized in terms of its dependence on extracellular calcium ion, its stimulus-response relationship, its sensitivity to the calcium-channel blocker omega conus toxin (omega-CgTx), and its modulation by the DHPs Bay K 8644 and nifedipine. Here it is reported that omega-CgTx (1 microM) blocked the electrically evoked release of SP. In contrast, the calcium-channel agonist Bay K 8644 (5 microM) facilitated the release of SP (by 45%), whereas the calcium-channel antagonist nifedipine (5 microM) was without effect. When the release of SP was triggered by depolarization of cultures with 60 mM KCI, the actions of the DHPs became much more pronounced. Under these conditions, Bay K 8644 facilitated (by 115%), whereas nifedipine inhibited (by 58%), peptide secretion. Voltage-clamp analysis of DRG cell calcium currents demonstrated that these actions of omega-CgTx, Bay K 8644, and nifedipine are explicable in terms of their effects on the slowly inactivating (L-type) calcium current. On the basis of these findings, it is suggested that the SP release mechanism exhibits DHP sensitivity due to the involvement of L-type calcium channels in the neurosecretory process. This model predicts that the voltage and time-dependent antagonist actions of nifedipine are sufficient to explain its failure to inhibit the electrically evoked release of SP.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1987

Dihydropyridine inhibition of neuronal calcium current and substance P release.

Dihydropyridine (DHP) calcium channel antagonists, which inhibit the slowly inactivating or L-type cardiac calcium (Ca) current, have been shown to be ineffective in blocking 45Ca influx and Ca-dependent secretion in a number of neuronal preparations. In the studies reported here, however, the antagonist DHP nifedipine inhibited both the L-type Ca current and potassium-evoked substance P (SP) release from embryonic chick dorsal root ganglion (DRG) neurons. These results suggest that, in DRG neurons, Ca entry through L-type channels is critical to the control of secretion. The inhibition of Ca current by nifedipine was both voltage and time-dependent, significant effects being observed only on currents evoked from relatively positive holding potentials maintained for several seconds. As expected from these results, nifedipine failed to inhibit L-type Ca current underlying the brief plateau phase of the action potential generated from the cell's normal resting potential; likewise, no significant effect of the drug was observed on action potential-stimulated SP release evoked by electrical field stimulation. The results of this work are discussed in terms of an assessment of the role of L-type Ca channels in neurosecretion.

Action Potentials↗
PubMed1986

A comparison of the cost of various treatment methods for early cancer of the prostate.

The relative costs have been determined for treating prostate cancer by radical prostatectomy, lymph node dissection with I125 implant, and external beam radiation in a large community practice. About 15% of patients were treated with the options involving surgery. The median cost of radical prostatectomy was $14,400, lymph dose dissection and I125 implant $12,000, and external beam radiation $6750 prior to October 1984 and $5600 after October 1984. None of the data indicate superior outcome by any one of these methods for Stage A or B prostate cancer. Therefore, the surgical approaches are usually not recommended except for the patient highly motivated to maintain potency who may select the I125 implant. In an era of diminishing funds for health care, the federal government, industry, and perceptive HMO's may elect to pay only for the less expensive method.

Brachytherapy↗
PubMed1986

Kinase C activator 1,2-oleoylacetylglycerol attenuates voltage-dependent calcium current in sensory neurons.

The diacylglycerol analogue 1,2-oleoylacetylglycerol (OAG) and the phorbol ester 12-deoxyphorbol 13-isobutyrate (DPB) were tested for their effects on the voltage-dependent calcium (Ca) current in embryonic chicken dorsal root ganglion neurons in vitro. OAG (0.6-60 microM) and DPB (0.01-50 microM) produced reversible decreases in Ca current. Neither drug affected resting membrane conductance, the voltage-dependent potassium current, or the Ca current-voltage relationship. The concentrations of OAG and DPB that reduced Ca current correlate well with those concentrations that have been shown, in other systems, to activate protein kinase C-dependent phosphorylation. The time course for OAG action on Ca current is also consistent with an involvement of kinase C. Incubation of dorsal root ganglion cells in 60 microM OAG prevented further reductions in Ca current by either 50 microM DPB or 10 microM norepinephrine, a known modulator of the voltage-dependent Ca channel in these cells. This evidence suggests that protein kinase C may play a role in modulating Ca channel function.

Animals↗
PubMed1985

Forskolin prolongs action potential duration and blocks potassium current in embryonic chick sensory neurons.

To determine if alterations in internal cyclic adenosine monophosphate (cAMP) play a role in modulation of voltage-dependent channels in embryonic chick sensory neurons in vitro, forskolin (a direct activator of adenylate cyclase) was tested on the cells. Forskolin, in concentrations between 1 and 100 microM, produced dose-dependent, reversible increases in action potential duration. This effect of forskolin was blocked by incubation of the neurons in 1 mM 2',5'-dideoxyadenosine, an inhibitor of forskolin-induced activation of cyclase in other cells. This suggests that the increase in action potential duration is likely to be mediated by activation of adenylate cyclase. Cholera toxin, another cyclase activator, also increased action potential duration when applied to the sensory neurons in a concentration of 10 micrograms/ml. Forskolin applied to voltage-clamped neurons decreased a voltage-dependent outward current, a result consistent with its effect on the action potential. These effects of forskolin are mimicked by capsaicin, but are in marked contrast to those previously reported for norepinephrine on the action potential and membrane currents (Dunlap and Fischbach 1981). Furthermore, forskolin does not block (or attenuate) the effects of norepinephrine, suggesting that increases in adenylate cyclase activity are most likely not involved in norepinephrine's action on the calcium channel.

Action Potentials↗
PubMed1984

Functional and pharmacological differences between two types of GABA receptor on embryonic chick sensory neurons.

Embryonic chick sensory neurons grown in dissociated cell culture exhibit two functional responses to GABA: an increase in resting membrane permeability to chloride (Cl) ions (resulting in membrane depolarization) and a decrease in voltage-dependent calcium (Ca) channel current (resulting in a decreased action potential duration). These two functional effects differ in a number of ways. (1) The increase in resting membrane permeability desensitizes in the maintained presence of GABA, while the decrease in action potential duration does not. (2) Muscimol is a selective agonist for the increase in resting conductance, while baclofen is a selective agonist for the decrease in action potential duration. (3) Bicuculline inhibits the GABA- or muscimol-induced increase in Cl permeability, but it does not block the GABA- or baclofen-induced decrease in action potential duration. These functional and pharmacological differences between the two effects of GABA suggest that two separate receptors are involved.

Animals↗
PubMed1984

Pharmacological characterization of amine receptors on embryonic chick sensory neurones.

The effects of noradrenaline, dopamine and 5-hydroxytryptamine were investigated on the duration of the action potential of embryonic chick sensory neurones in vitro. All three amines, like gamma-aminobutyric acid, decreased the duration of the action potential evoked by current injection. The onset of the noradrenaline-induced decrease in action potential duration was fast (less than 1s) and the recovery phase was dependent upon the dose of noradrenaline applied. Rapid washout of the noradrenaline revealed a minimum 30s recovery time which was independent of the initial noradrenaline concentration. Dopamine and 5-hydroxytryptamine could mimic the effects of noradrenaline on action potential duration. The ED50 for all three amines was approximately 1 microM. At a saturating concentration of 10 microM, noradrenaline was more potent than dopamine and 5-hydroxytryptamine. Saturating doses of noradrenaline and dopamine or 5-hydroxytryptamine were not additive. Responses to all three amines were affected similarly by antagonists: they were antagonized by yohimbine, phentolamine, haloperidol and mianserin but not by propranolol, prazosin, domperidone, spiperone or methysergide. Clonidine and xylazine (alpha 2-adrenoceptor agonists) were also without effect. In contrast to the amines, saturating concentrations of gamma-aminobutyric acid were additive with those of noradrenaline. Responses to GABA were not antagonized by the amine receptor antagonists. The evidence described here suggests that the amines and gamma-aminobutyric acid acid decrease sensory neurone action potential duration via pharmacologically-distinct membrane receptors. In addition, it is likely that the amines are acting via a single class of receptor whose pharmacology is different from classical adrenoceptors, dopamine receptors and 5-hydroxytryptamine receptors.

Action Potentials↗
PubMed1981

Two types of gamma-aminobutyric acid receptor on embryonic sensory neurones.

1 Embryonic sensory neurones of the chick grown in dissociated cell culture respond to application of low concentrations of gamma-aminobutyric acid (GABA) with a change in resting membrane resistance (R(in)) and/or a change in action potential duration (APD) (Dunlap & Fischbach, 1978; Choi & Fischbach, 1981). Intracellular microelectrode recording techniques were employed to determine if these two effects are mediated by the same, or different, GABA receptors.2 Cells responded, for the most part, with a change in either R(in) or APD, but 10% of the cells exhibited both effects. In the latter cells the two responses were clearly distinguishable as discussed below.3 The proportion of neurones exhibiting a GABA-induced decrease in R(in) declined during the first week in vitro while the proportion exhibiting a decrease in APD increased during that time.4 The two effects were pharmacologically distinct. Muscimol, a GABA analogue, produced only the change in R(in) (ED(50) = 5.5 muM) while baclofen, another analogue of GABA, produced only the change in APD (ED(50) = 1 muM). The analogues were approximately equipotent with GABA. Bicuculline, a GABA antagonist, blocked the muscimol-induced change in R(in) (but not the baclofen-induced change in APD) in a dose-dependent fashion with an ID(50) = 0.7 muM.5 The time courses of the two effects were different. The change in APD resulting from a brief application of GABA (or baclofen) was prolonged relative to the rapid return to control associated with the GABA- (or muscimol-) induced change in R(in).6 Desensitization of the two responses exhibited separate time courses. In the continual presence of the agonists, GABA- and muscimol-induced decreases in R(in) completely desensitized in ca. 10 s while GABA- and baclofen-induced decreases in APD persisted undiminished throughout a prolonged (1 min) application of the drugs and returned to control only after cessation of application.7 It is concluded that embryonic chick sensory neurones in culture exhibit two types of GABA receptor that differ in their functional and pharmacological properties. Implications of these results are discussed.

Action Potentials↗
PubMed1981

Neurotransmitters decrease the calcium conductance activated by depolarization of embryonic chick sensory neurones.

Several neurotransmitters including noradrenaline (NA), gamma-aminobutyric acid (GABA) and serotonin (5-HT), and also certain peptides, decrease the duration of the Na+-Ca2+ action potential recorded in cell bodies of embryonic chick dorsal root ganglion neurones maintained in cell culture. To determine if these agents decreased action potential duration by affecting Ca2+ channels (inward current) or K+ channels (outward current) membrane currents were recorded in voltage-clamped sensory neurone somata. 1. Depolarization produced a prominent inward Na+ current and a smaller and slower inward Ca2+ current (ICa). The inactivation of ICa was not simply dependent on membrane potential but apparently required prior entry of Ca2+. Two components of outward current, voltage-activated and Ca2+-activated, were evident in most cells. 2. The effect of NA, and also of GABA and 5-HT, was shown to result from a direct effect on ICa because: NA decreased the TTX-resistant tail current recorded at EK and also the inward current recorded in the presence of 125 mM-TEA and TTX (in which Na+ and K+ currents were blocked). 3. The decrease in ICa is most likely due to an effect on the number of available Ca2+ channels and/or the single Ca2+ channel conductance rather than to a shift in either the kinetics of channel activation or the Ca2+ equilibrium potential. 4. No effect of the several transmitters on the voltage-dependent Na+ and K+ currents was observed. 5. Implications of ICa modulation for the phenomenon of presynaptic inhibition are discussed.

Action Potentials↗
PubMed1981

Peptide and amine transmitter effect on embryonic chick sensory neurons in vitro.

It has been known for some time that NE and ACh can affect voltage-sensitive channels in the heart but it has only recently been appreciated that neurotransmitters (and certain peptides) can modulate voltage-sensitive channels in neurons. In addition to the effect on the action potential of embryonic chick sensory neurons described here, NE decreases the duration of spikes in rat superior cervical ganglion neurons (7). Serotonin prolongs action potentials recorded in Aplysia sensory neurons (9) and an as yet unidentified transmitter decreases an inward Ca++ current in the same cells (20). In the heart, one important consequence of the effect of NE and ACh on the action potential is a change in the strength and/or duration of contraction. In neurons, attention has been focused on the possibility that modulation of voltage-sensitive channels might result in a change in transmitter release. In Aplysia, the 5-HT induced prolongation of sensory neuron some spikes is associated with a dramatic augmentation of transmitter release at sensory nerve-motorneurone synapses (9) and the decrease in some inward Ca++ current is associated with presynaptic inhibition (20). Enkephalin, NE, GABA, and 5-HT can inhibit the evoked release of Substance P from cultured embryonic chick sensory neurons. These same drugs decrease ICa, apparently by decreasing the number of the conductance of voltage-sensitive Ca++ channels. The two phenomena may be related. It is significant in this regard that the same variability (between platings) in the ability of enkephalin to reduce Substance P release was also observed in the effect of enkephalin on action potential duration. Cells that released normal amounts of Substance P in the presence of enkephalin also exhibit spikes of normal duration in the presence of the peptide.

Acetylcholine↗
PubMed1978

Calcium-dependent repolarization in Paramecium.

1. Intracellular injection, recording and current-passing methods were used to investigate the role of intracellular Ca in the modulation of electrical behaviour in the ciliate Paramecium caudatum.2. Injection of EGTA converted graded regenerative responses ascribed to Ca inward current to all-or-none action potentials. The EGTA injection also caused a discontinuity in the steady state I-V relations to outward current, but had little effect on hyperpolarizing current-voltage responses.3. The overshoot of the all-or-none spike produced by the EGTA-injected cell followed an approximate 29 mV increase for a tenfold increase in external Ca concentration and was independent of changes in external K and Na concentrations.4. The EGTA-induced all-or-none action potential tended to produce plateaus that could last up to 20 sec. During the plateau the membrane slowly repolarized to a critical potential, upon which repolarization occurred precipitously.5. Injection of 10(-6)M-free Ca(2+) as a Ca-EGTA buffer hyperpolarized the membrane and decreased the potential shifts to inward current pulses. These responses are consistent with an increase in K conductance.6. During EGTA plateaus reversed beating of the cilia indicated a rise in intracellular Ca, and thus an inability of the EGTA to complex the Ca as rapidly as it entered the cilia. Reversal of the motile apparatus thus appears to be activated at lower concentrations of intracellular Ca than are required to activate the inferred Ca-dependent K system.7. In uninjected cells removal of the cilia, which results in a loss of the voltage-activated Ca channels (Dunlap, 1977), or addition of extracellular Ba both tended to linearize the steady state I-V relations.8. Injections of Cs and TEA tended to linearize the steady state I-V relations, but did not result in either a conversion to an all-or-none spike or a discontinuity in the depolarizing steady-state I-V relations.9. It is concluded that in Paramecium a Ca-activated K conductance short-circuits the inward current of the regenerative Ca response, preventing all-or-none behaviour. The occurrence of plateau spikes following EGTA injection indicates that the Ca conductance inactivates very slowly in face of a maintained depolarization. Such slow Ca-inactivation is consistent with the slow relaxation of Ca-dependent ciliary reversal that occurs during maintained depolarization.10. The possibility is discussed that injection of EGTA may also enhance the Ca conductance.

Action Potentials↗
PubMed1977

Localization of calcium channels in Paramecium caudatum.

1. Electrical recordings from Paramecium caudatum were made after removal of the cilia with chloral hydrate and during ciliary regrowth to study the electrical properties of that portion of the surface membrane enclosing the ciliary axoneme. 2. Removal of the somatic cilia (a 50% reduction in membrane surface area) results in an almost complete elimination of the regenerative Ca response, all-or-none Ba2+ spike, and delayed rectification. 3. A twofold increase in input resistance resulted from the 50% reduction in membrane surface area. 4. The electrical properties remained unchanged, despite prolonged exposure to the chloral hydrate, until the cilia were mechanically removed. 5. Restoration of the Ca response accompanied ciliary regrowth, so that complete excitability returns when the cilia regain their original lengths. 6. It is concluded that the voltage-sensitive Ca channels are localized to that portion of surface membrane surrounding the cilia. 7. Measurements of membrane constants before and after deciliation and estimations of the cable constants of a single cilium suggest that the cilia of Paramecium may be fully isopotential along their length and with the major cell compartment.

Action Potentials↗