Vasopressin-Induced Currents in Rat Neonatal Spinal Lateral Horn Neurons Are G-Protein Mediated and Involve Two Conductances

1998 ◽  
Vol 80 (4) ◽  
pp. 1900-1910 ◽  
Author(s):  
Miloslav Kolaj ◽  
Leo P. Renaud

Kolaj, Miloslav and Leo P. Renaud. Vasopressin-induced currents in rat neonatal spinal lateral horn neurons are G-protein mediated and involve two conductances . J. Neurophysiol. 80: 1900–1910, 1998. Arginine vasopressin (AVP) receptors are expressed early in the developing spinal cord. To characterize AVP-induced conductances in lower thoracic sympathetic preganglionic (SPN) and other lateral horn neurons, we used patch-clamp recording techniques in neonatal (11–21 days) rat spinal cord slices. Most (90%) of 273 neurons, including all 68 SPNs, responded to AVP with membrane depolarization and/or a V1 receptor-mediated, dose-dependent (0.01–1.0 μM) and tetrodotoxin (TTX)-resistant inward current. A role for G-proteins was indicated by persistence of this inward current after intracellular dialysis with GTP-γ-S or GMP-PNP, its marked reduction with GDP-β-S, and significant reduction, but not abolition, after preincubation with pertussis toxin or in the presence of N-ethylmaleimide. Analysis of individual current-voltage ( I- V) relationships in 57 cells indicated the presence of two different membrane conductances. In 21 cells, net AVP-induced currents reversed around −103 mV, reflecting reduction in one or more barium-sensitive potassium conductances; in 12 cells, net AVP-induced current reversed around −40 mV and was not significantly sensitive to several potassium channel blockers including barium, tetraethylammonium chloride (TEA), 4-aminopyridine (4AP), cesium, or glibenclamide, suggesting increase in a nonselective cationic conductance that was separate from I h; in 24 cells where I- V lines shifted in parallel, AVP-induced inward currents were significantly greater and probably involved both conductances. These data indicate that SPNs and a majority of unidentified neonatal lateral horn neurons possess functional G-protein–coupled V1-type vasopressin receptors. The wide distribution of AVP receptors in neonatal spinal lateral column cells suggests a role that may extend beyond involvement in regulation of autonomic nervous system function.

1997 ◽  
Vol 78 (3) ◽  
pp. 1726-1729 ◽  
Author(s):  
Miloslav Kolaj ◽  
Susan J. Shefchyk ◽  
Leo P. Renaud

Kolaj, Miloslav, Susan J. Shefchyk, and Leo P. Renaud. Two conductances mediate thyrotropin-releasing-hormone-induced depolarization of neonatal rat spinal preganglionic and lateral horn neurons. J. Neurophysiol. 78: 1726–1729, 1997. Thyrotropin-releasing hormone (TRH) has been recognized as a neuromodulator in several CNS regions, including the thoracolumbar spinal cord where an influence on cardiovascular autonomic function has been proposed. To identify the cellular mechanisms involved in the latter, whole cell patch-clamp recordings were obtained from 52 thoracolumbar lateral horn cells, including 17 sympathetic preganglionic neurons (SPNs), in spinal cord slices from neonatal rat (11–21 days). Under current clamp, bath applications of TRH (1–20 μM) induced a slowly rising and prolonged membrane depolarization in eight of nine cells tested. Under voltage clamp (holding potential −65 mV), 33 of 37 tested cells displayed a TRH-induced, tetrodotoxin-resistant inward current that was associated with either a reduction or an increase in membrane ion conductances. Current-voltage ( I-V) relationships in 28 cells suggested two conductances. In 9 cells the current reversed at about −107 mV; in 10 cells the I-V lines remained parallel, whereas in 9 cells the current reversed at around −40 mV. In three of three cells, addition of 2 mM barium was associated with an inward current, and the TRH-induced inward current was also suppressed, suggesting the presence of a resting barium- and TRH-sensitive potassium conductance. A residual barium-insensitive conductance was seen to reverse near −40 mV. Intracellular dialysis with guanosine 5′- o-(3-thiotriphosphate) significantly enhanced the duration of the TRH effect, indicating that G protein activation participates in the TRH response. These observations not only reveal a direct, G-protein-mediated depolarizing action of TRH on neonatal rat SPNs and lateral horn cells but also imply that two separate conductances may be involved in the TRH responses in some neurons.


Author(s):  
Ji Yeon Lee ◽  
Haifeng Zheng ◽  
Kenton M. Sanders ◽  
Sang Don Koh

We characterized the two types of voltage-dependent inward currents in murine antral SMC. The HVA and LVA inward currents were identified when cells were bathed in Ca2+-containing physiological salt solution. We examined whether the LVA inward current was due to: 1) T-type Ca2+ channels, 2) Ca2+-activated Cl- channels, 3) non-selective cation channels (NSCC) or 4) voltage-dependent K+ channels with internal Cs+-rich solution. Replacement of external Ca2+ (2 mM) with equimolar Ba2+ increased the amplitude of the HVA current but blocked the LVA current. Nicardipine blocked the HVA current, and in the presence of nicardipine, T-type Ca2+ blockers failed to block LVA. The Cl- channel antagonist had little effect on LVA. Cation-free external solution completely abolished both HVA and LVA. Addition of Ca2+ in cation-free solution restored only HVA currents. Addition of K+ (5 mM) to cation-free solution induced LVA current that reversed at -20 mV. These data suggest that LVA is not due to T-type Ca2+ channels, Ca2+-activated Cl- channels or NSCC. Antral SMC express A-type K+ currents (KA) and delayed rectifying K+ currents (KV) with dialysis of high K+ (140 mM) solution. When cells were exposed to high K+ external solution with dialysis of Cs+-rich solution in the presence of nicardipine, LVA was evoked and reversed at positive potentials. These HK-induced inward currents were blocked by K+ channel blockers, 4-aminopyridine and TEA. In conclusion, LVA inward currents can be generated by K+ influx via KA and KV channels in murine antral SMC when cells were dialyzed with Cs+-rich solution.


2007 ◽  
Vol 98 (3) ◽  
pp. 1108-1114 ◽  
Author(s):  
Murat Oz ◽  
Keun-Hang Yang ◽  
Toni S. Shippenberg ◽  
Leo P. Renaud ◽  
Michael J. O'Donovan

Reports of cholecystokinin (CCK) binding and expression of CCK receptors in neonatal rodent spinal cord suggest that CCK may influence neuronal excitability. In patch-clamp recordings from 19/21 ventral horn motoneurons in neonatal (PN 5–12 days) rat spinal cord slices, we noted a slowly rising and prolonged membrane depolarization induced by bath-applied sulfated CCK octapeptide (CCK-8s; 1 μM), blockable by the CCKB receptor antagonist L-365,260 (1 μM). Responses to nonsulfated CCK-8 or CCK-4 were significantly weaker. Under voltage clamp ( VH −65 mV), 22/24 motoneurons displayed a CCK-8s-induced tetrodotoxin-resistant inward current [peak: −136 ± 28 pA] with a similar time course, mediated via reduction in a potassium conductance. In 29/31 unidentified neurons, CCK-8s induced a significantly smaller inward current (peak: −42.8 ± 5.6 pA), and I-V plots revealed either membrane conductance decrease with net inward current reversal at 101.3 ± 4.4 mV ( n = 16), membrane conductance increase with net current reversing at 36.1 ± 3.8 mV ( n = 4), or parallel shift ( n = 9). Intracellular GTP-γ-S significantly prolonged the effect of CCK-8s ( n = 6), whereas GDP-β-S significantly reduced the CCK-8s response ( n = 6). Peak inward currents were significantly reduced after 5-min perfusion with N-ethylmaleimide. In isolated neonatal mouse spinal cord preparations, CCK-8s (30–300 nM) increased the amplitude and discharge of spontaneous depolarizations recorded from lumbosacral ventral roots. These observations imply functional postsynaptic G-protein-coupled CCKB receptors are prevalent in neonatal rodent spinal cord.


1999 ◽  
Vol 81 (3) ◽  
pp. 1424-1427 ◽  
Author(s):  
Diana L. Pettit ◽  
Matthew C. Helms ◽  
Psyche Lee ◽  
George J. Augustine ◽  
William C. Hall

Local excitatory circuits in the intermediate gray layer of the superior colliculus. We have used photostimulation and whole cell patch-clamp recording techniques to examine local synaptic interactions in slices from the superior colliculus of the tree shrew. Uncaging glutamate 10–75 μm from the somata of neurons in the intermediate gray layer elicited a long-lasting inward current, due to direct activation of glutamate receptors on these neurons, and brief inward currents caused by activation of presynaptic neurons. The synaptic responses occurred as individual currents or as clusters that lasted up to several hundred milliseconds. Excitatory synaptic responses, which reversed at membrane potentials near 0 mV, could be evoked by uncaging glutamate anywhere within 75 μm of an intermediate layer neuron. Our results indicate the presence of extensive local excitatory circuits in the intermediate layer of the superior colliculus and support the hypothesis that such intrinsic circuitry contributes to the development of presaccadic command bursts.


1998 ◽  
Vol 275 (5) ◽  
pp. C1201-C1206 ◽  
Author(s):  
Kouhei Inamura ◽  
Makoto Kashiwayanagi ◽  
Kenzo Kurihara

The effects of cGMP and sodium nitroprusside (SNP) on odor responses in isolated turtle olfactory neurons were examined. The inward current induced by dialysis of a mixture of 1 mM cAMP and 1 mM cGMP was similar to that induced by dialysis of 1 mM cAMP or 1 mM cGMP alone. After the neurons were desensitized by the application of 1 mM cGMP, 3 mM 8-(4-chlorophenylthio)-cAMP, a membrane-permeable cAMP analog, did not elicit any current, indicating that both cAMP and cGMP activated the same channel. Extracellular application of SNP, a nitric oxide (NO) donor, evoked inward currents in a dose-dependent manner. However, application of SNP did not induce any currents after desensitization of the cGMP-induced currents, suggesting that SNP-induced currents are mediated via the cGMP-dependent pathway. Application of the cAMP-producing odorants to the neurons induced a large inward current even after neurons were desensitized to a high concentration of cGMP or SNP. These results suggest that the transduction pathway independent of cAMP, cGMP, and NO also contributes to the generation of odor responses in addition to the cAMP-dependent pathway.


2001 ◽  
Vol 86 (5) ◽  
pp. 2173-2182 ◽  
Author(s):  
Abdallah Hayar ◽  
Phillip M. Heyward ◽  
Thomas Heinbockel ◽  
Michael T. Shipley ◽  
Matthew Ennis

The main olfactory bulb receives a significant modulatory noradrenergic input from the locus coeruleus. Previous in vivo and in vitro studies showed that norepinephrine (NE) inputs increase the sensitivity of mitral cells to weak olfactory inputs. The cellular basis for this action of NE is not understood. The goal of this study was to investigate the effect of NE and noradrenergic agonists on the excitability of mitral cells, the main output cells of the olfactory bulb, using whole cell patch-clamp recording in vitro. The noradrenergic agonists, phenylephrine (PE, 10 μM), isoproterenol (Isop, 10 μM), and clonidine (3 μM), were used to test for the functional presence of α1-, β-, and α2-receptors, respectively, on mitral cells. None of these agonists affected olfactory nerve (ON)–evoked field potentials recorded in the glomerular layer, or ON-evoked postsynaptic currents recorded in mitral cells. In whole cell voltage-clamp recordings, NE (30 μM) induced an inward current (54 ± 7 pA, n= 16) with an EC50 of 4.7 μM. Both PE and Isop also produced inward currents (22 ± 4 pA, n = 19, and 29 ± 9 pA, n = 8, respectively), while clonidine produced no effect ( n = 6). In the presence of TTX (1 μM), and blockers of excitatory and inhibitory fast synaptic transmission [gabazine 5 μM, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) 10 μM, and (±)-2-amino-5-phosphonopentanoic acid (APV) 50 μM], the inward current induced by PE persisted (EC50 = 9 μM), whereas that of Isop was absent. The effect of PE was also observed in the presence of the Ca2+ channel blockers, cadmium (100 μM) and nickel (100 μM). The inward current caused by PE was blocked when the interior of the cell was perfused with the nonhydrolyzable GDP analogue, GDPβS, indicating that the α1 effect is mediated by G-protein coupling. The current-voltage relationship in the absence and presence of PE indicated that the current induced by PE decreased near the equilibrium potential for potassium ions. In current-clamp recordings from bistable mitral cells, PE shifted the membrane potential from the downstate (−52 mV) toward the upstate (−40 mV), and significantly increased spike generation in response to perithreshold ON input. These findings indicate that NE excites mitral cells directly via α1 receptors, an effect that may underlie, at least in part, increased mitral cell responses to weak ON input during locus coeruleus activation in vivo.


2003 ◽  
Vol 94 (1) ◽  
pp. 301-313 ◽  
Author(s):  
Tom Karkanis ◽  
Ling DeYoung ◽  
Gerald B. Brock ◽  
Stephen M. Sims

Little is known of the excitatory mechanisms that contribute to the tonic contraction of the corpus cavernosum smooth muscle in the flaccid state. We used patch-clamp electrophysiology to investigate a previously unidentified inward current in freshly isolated rat and human corporal myocytes. Phenylephrine (PE) contracted cells and activated whole cell currents. Outward current was identified as large-conductance Ca2+-activated K+ current. The inward current elicited by PE was dependent on the Cl− gradient and was inhibited by niflumic acid, indicative of a Ca2+-activated Cl− (ClCa) current. Furthermore, spontaneous transient outward and inward currents (STOCs and STICs, respectively) were identified in both rat and human corporal myocytes and derived from large-conductance Ca2+-activated K+ and ClCa channel activity. STICs and STOCs were inhibited by PE and A-23187, and combined 8-bromoadenosine cAMP and 8-bromoadenosine cGMP decreased their frequency. When studied in vivo, chloride channel blockers transiently increased intracavernosal pressure and prolonged nerve-evoked erections. This report reveals for the first time ClCa current in rat and human corpus cavernosum smooth muscle cells and demonstrates its key functional role in the regulation of penile erection.


1994 ◽  
Vol 71 (5) ◽  
pp. 1935-1947 ◽  
Author(s):  
K. Kawa

1. In dentate gyrus of rat hippocampal slices two distinct types of neurons, principal excitatory neurons (granule cells) and local inhibitory neurons (basket cells), could be identified under Nomarski microscopy; I investigated the actions of serotonin using the whole-cell patch-clamp technique. The identification of the neurons was later confirmed by intracellular staining with Lucifer yellow. 2. In both basket cells and granule cells, whole-cell current recordings revealed spontaneous synaptic currents ranging from < 10 pA to > 200 pA in symmetrical Cl- conditions at a holding potential of -63 mV. These currents were blocked by 10 microM bicuculline, indicating that they resulted from the spontaneous activation of GABAergic inputs (which had been morphologically described in both types of neurons). 3. By focal application of serotonin (2–50 microM) to basket cells under current clamp I evoked a train of action potentials superimposed on a baseline membrane depolarization. Under voltage-clamp conditions serotonin evoked an inward current at a holding potential of -63 mV (currents were detectable in approximately 90% of basket cells studied). The inward current was accompanied by a multitude of small inward currents of short duration (< 100 ms) that were found to be due to the stimulation by serotonin of nearby GABAergic presynaptic neurons innervating the recorded neuron. 4. In granule cells (total of 11 cells) serotonin did not produce any responses under conditions similar to those used for basket cells. The occurrence of bicuculline-sensitive spontaneous synaptic current events seemed to increase during the application of serotonin; this phenomenon reflected the excitatory action of serotonin exclusively on GABAergic interneurons. 5. The serotonin-induced inward currents in basket cells were mediated by the 5-HT3 receptor subtype because 1) they were blocked by either metoclopramide (10 microM) or [3-alpha-tropanyl]-1H-indolecarboxylic acid ester (2 nM), the latter being a specific blocker for the 5-HT3 receptor subtype, and 2) almost similar currents were induced by the application of the selective 5-HT3 receptor agonist 2-methyl 5-HT (2–50 microM) or 1-(m-chlorophenyl)-biguanide (0.1–10 microM). 6. Current-voltage (I–V) relations of serotonin-induced currents in basket cells showed that the reversal potential was close to 0 mV in external standard saline and depended on the concentrations of monovalent cations. I–V relations of serotonin-induced currents revealed inward rectification at the membrane potential range of +30 to -60 mV.(ABSTRACT TRUNCATED AT 400 WORDS)


1993 ◽  
Vol 69 (2) ◽  
pp. 432-441 ◽  
Author(s):  
N. Hershkowitz ◽  
A. N. Katchman ◽  
S. Veregge

1. The effect of hypoxia on synaptic physiology was investigated in hippocampal slices from 16- to 23-day-old rats. CA1 pyramidal cells were examined by whole cell patch-clamp recording, and hypoxia was induced by switching perfusion of the slice from oxygenated artificial cerebrospinal fluid (ACSF) to ACSF saturated with 95% N2-5%CO2. Synaptic responses were assessed by stimulating the Schaffer collateral-commissural projection with an electrode in the stratum radiatum every 20 s. 2. Within 100-200 s of the onset of hypoxia, the orthrodromically elicited synaptic response of the CA1 cells was largely inhibited. In addition, a slow inward current was observed after the onset of hypoxia. A transient outward current, preceding the inward current, was observed in only 2 of 17 cells examined. The slow inward current culminated in an irreversible rapid inward current at approximately 140 s after hypoxia. This rapid inward current occurred simultaneously with spreading depression as measured by field potentials. Tetrodotoxin (TTX) had no effect on the onset of this current, whereas kynurenic acid significantly delayed its occurrence. 3. Before the onset of hypoxia, spontaneous transient inward currents were apparent. The frequency of these events increased by three- to fourfold after hypoxia. The transient inward currents persisted in slices incubated in TTX, but were almost completely inhibited in slices incubated with the mixed N-methyl-D-aspartate (NMDA)/non-NMDA antagonist kynurenic acid. This identified the spontaneous events that were increased in frequency by hypoxia as glutamatergic miniature excitatory postsynaptic currents (mEPSCs). 4. The mean amplitude of the mEPSCs was not affected by hypoxia at a time at which the orthodromically elicited synaptic response was almost completely inhibited by hypoxia. In addition, the response of the postsynaptic cell to pressure ejection of glutamate was not inhibited under conditions of nearly complete blocked the synaptic response. Thus, by two measures, the postsynaptic response was not affected by hypoxia, indicating that the site of hypoxia-induced synaptic failure was at the presynaptic terminal. 5. The orthodromically elicited synaptic response consisted of an EPSC followed closely by an inhibitory postsynaptic current (IPSC). The IPSC portion of the elicited postsynaptic response was more sensitive to inhibition by hypoxia than was the EPSC. In some cells the EPSC exhibited a monophasic decline in amplitude during hypoxia. However, in a majority of cells, an initial decline in the amplitude of the EPSC was followed by a transient increase and subsequent depression.(ABSTRACT TRUNCATED AT 400 WORDS)


2012 ◽  
Vol 303 (4) ◽  
pp. C376-C384 ◽  
Author(s):  
Qiu-Ju Xiong ◽  
Zhuang-Li Hu ◽  
Peng-Fei Wu ◽  
Lan Ni ◽  
Zhi-Fang Deng ◽  
...  

Acid-sensing ion channels (ASICs) have been reported to play a role in the neuronal dopamine pathway, but the exact role in neurotransmitter release remains elusive. Human neuroblastoma SH-SY5Y is a dopaminergic neuronal cell line, which can release monoamine neurotransmitters. In this study, the expression of ASICs was identified in SH-SY5Y cells to further explore the role of ASICs in vesicular release stimulated by acid. We gathered evidence that ASICs could be detected in SH-SY5Y cells. In whole cell patch-clamp recording, a rapid decrease in extracellular pH evoked inward currents, which were reversibly inhibited by 100 μM amiloride. The currents were pH dependent, with a pH of half-maximal activation (pH0.5) of 6.01 ± 0.04. Furthermore, in calcium imaging and FM 1-43 dye labeling, it was shown that extracellular protons increased intracellular calcium levels and vesicular release in SH-SY5Y cells, which was attenuated by PcTx1 and amiloride. Interestingly, N-type calcium channel blockers inhibited the vesicular release induced by acidification. In conclusion, ASICs are functionally expressed in SH-SY5Y cells and involved in vesicular release stimulated by acidification. N-type calcium channels may be involved in the increase in vesicular release induced by acid. Our results provide a preliminary study on ASICs in SH-SY5Y cells and neurotransmitter release, which helps to further investigate the relationship between ASICs and dopaminergic neurons.


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