Group I mGluR Activation Causes Voltage-Dependent and -Independent Ca2+ Rises in Hippocampal Pyramidal Cells

1999 ◽  
Vol 81 (6) ◽  
pp. 2903-2913 ◽  
Author(s):  
Riccardo Bianchi ◽  
Steven R. Young ◽  
Robert K. S. Wong
Keyword(s):  
Metabotropic Glutamate Receptor ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Membrane Depolarization ◽  
Membrane Hyperpolarization ◽  
Voltage Gated ◽  
Group I ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
Hippocampal Pyramidal Cells

Group I mGluR activation causes voltage-dependent and -independent Ca2+ rises in hippocampal pyramidal cells. Application of the metabotropic glutamate receptor (mGluR) agonist (1 S,3 R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) or the selective group I mGluR agonist ( S)-3,5-dihydroxyphenylglycine (DHPG) depolarized both CA3 and CA1 pyramidal cells in guinea pig hippocampal slices. Simultaneous recordings of voltage and intracellular Ca2+ levels revealed that the depolarization was accompanied by a biphasic elevation of intracellular Ca2+ concentration ([Ca2+]i): a transient calcium rise followed by a delayed, sustained elevation. The transient [Ca2+]i rise was independent of the membrane potential and was blocked when caffeine was added to the perfusing solution. The sustained [Ca2+]i rise appeared when membrane depolarization reached threshold for voltage-gated Ca2+ influx and was suppressed by membrane hyperpolarization. The depolarization was associated with an increased input resistance and persisted when either the transient or sustained [Ca2+]i responses was blocked. mGluR-mediated voltage and [Ca2+]i responses were blocked by (+)-α-methyl-4-carboxyphenylglycine (MCPG) or ( S)-4-carboxy-3-hydroxyphenylglycine (4C3HPG). These data suggest that in both CA3 and CA1 hippocampal cells, activation of group I mGluRs produced a biphasic accumulation of [Ca2+]i via two paths: a transient release from intracellular stores, and subsequently, by influx through voltage-gated Ca2+ channels. The concurrent mGluR-induced membrane depolarization was not caused by the [Ca2+]i rise.

Group I mGluR Activation Turns on a Voltage-Gated Inward Current in Hippocampal Pyramidal Cells

2000 ◽  
Vol 83 (5) ◽  
pp. 2844-2853 ◽  
Author(s):  
Shih-Chieh Chuang ◽  
Riccardo Bianchi ◽  
Robert K. S. Wong
Keyword(s):  
Metabotropic Glutamate Receptor ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Calcium Currents ◽  
Resting Potential ◽  
Inward Current ◽  
Voltage Gated ◽  
Group I ◽  
Ionic Mechanisms ◽  
Ca3 Pyramidal Cells

A unique property of the group I metabotropic glutamate receptor (mGluR)-induced depolarization in hippocampal cells is that the amplitude of the depolarization is larger when the response is elicited at more depolarized membrane potentials. Our understanding of the conductance mechanism underlying this voltage-dependent response is incomplete. Through the use of current-clamp and single-electrode voltage-clamp recordings in guinea pig hippocampal slices, we examined the group I mGluR-induced depolarization in CA3 pyramidal cells. The group I mGluR agonists ( S)-3-hydroxyphenylglycine and ( S)-3,5-dihydroxyphenylglycine turned on a voltage-gated inward current ( I mGluR(V)), which was pharmacologically distinct from the voltage-gated sodium and calcium currents intrinsic to the cells. I mGluR(V)was a slowly activating, noninactivating current with a threshold at about −75 mV. In addition to the activation of I mGluR(V), group I mGluR stimulation also produced a voltage-independent decrease in the K+conductance. Our results suggest that the depolarization induced by group I mGluR activation is generated by two ionic mechanisms—a heretofore unrecognized voltage-gated inward current ( I mGluR(V)) that is turned on by depolarization and a voltage-insensitive inward current that results from a turn-off of the K+ conductance. The low-threshold and noninactivating properties of I mGluR(V)allow the current to play a significant role in setting the resting potential and firing pattern of CA3 pyramidal cells.

Requirement of Protein Synthesis for Group I mGluR-Mediated Induction of Epileptiform Discharges

1998 ◽  
Vol 80 (2) ◽  
pp. 989-993 ◽  
Author(s):  
Lisa R. Merlin ◽  
Peter J. Bergold ◽  
Robert K. S. Wong
Keyword(s):  
Protein Synthesis ◽  
Metabotropic Glutamate Receptor ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Progressive Increase ◽  
Protein Synthesis Inhibitors ◽  
Burst Frequency ◽  
Metabotropic Glutamate ◽  
Epileptiform Discharges ◽  
Group I

Merlin, Lisa R., Peter J. Bergold, and Robert K. S. Wong. Requirement of protein synthesis for group I mGluR-mediated induction of epileptiform discharges. J. Neurophysiol. 80: 989–993, 1998. Picrotoxin (50 μM) elicited rhythmic synchronized bursting in CA3 pyramidal cells in guinea pig hippocampal slices. Addition of the selective group I metabotropic glutamate receptor (mGluR) agonist ( S)-3,5-dihydroxyphenylglycine (25 μM) elicited an increase in burst frequency. This was soon followed by a slowly progressive increase in burst duration (BD), converting the brief 250–520 ms picrotoxin-induced synchronized bursts into prolonged discharges of 1–5 s in duration. BD was significantly increased within 60 min and reached a maximum after 2–2.5 h of agonist exposure. The protein synthesis inhibitors anisomycin (15 μM) or cycloheximide (25 μM) significantly impeded the mGluR-mediated development of the prolonged bursts; 90–120 min of agonist application failed to elicit the expected burst prolongation. By contrast, the mGluR-mediated enhancement of burst frequency progressed unimpeded. Furthermore, protein synthesis inhibitors had no significant effect on the frequency or duration of fully developed mGluR-induced prolonged discharges. These results suggest that the group I mGluR-mediated prolongation of synchronized bursts has a protein synthesis-dependent mechanism.

Metabotropic Glutamate Receptor Agonists Alter Neuronal Excitability and Ca2+ Levels via the Phospholipase C Transduction Pathway in Cultured Purkinje Neurons

1997 ◽  
Vol 78 (1) ◽  
pp. 63-75 ◽  
Author(s):  
Jeffrey G. Netzeband ◽  
Kathy L. Parsons ◽  
Dan D. Sweeney ◽  
Donna L. Gruol
Keyword(s):  
Phospholipase C ◽  
Glutamate Receptor ◽  
Neuronal Excitability ◽  
Metabotropic Glutamate Receptor ◽  
Purkinje Neurons ◽  
Transduction Pathway ◽  
Electrophysiological Response ◽  
Metabotropic Glutamate ◽  
Group I ◽  
Intracellular Ca

Netzeband, Jeffrey G., Kathy L. Parsons, Dan D. Sweeney, and Donna L. Gruol. Metabotropic glutamate receptor agonists alter neuronal excitability and Ca2+ levels via the phospholipase C transduction pathway in cultured Purkinje neurons. J. Neurophysiol. 78: 63–75, 1997. Selective agonists for metabotropic glutamate receptor (mGluR) subtypes were tested on mature, cultured rat cerebellar Purkinje neurons (≥21 days in vitro) to identify functionally relevant mGluRs expressed by these neurons and to investigate the transduction pathways associated with mGluR-mediated changes in membrane excitability. Current-clamp recordings (nystatin/perforated-patch method) were used to measure the membrane response of Purkinje neurons to brief microperfusion pulses (1.5 s) of the group I (mGluR1/mGluR5) agonists (1 S,3 R)-1-aminocyclopentane-1,3-dicarboxylic acid (300 μM), quisqualate (5 μM), and ( R,S)-3,5-dihydroxyphenylglycine (50–500 μM). All group I mGluR agonists elicited biphasic membrane responses and burst activity in the Purkinje neurons. In addition, the group I mGluR agonists produced alterations in the active membrane properties of the Purkinje neurons and depressed the off response after hyperpolarizing current injection. In parallel microscopic Ca2+ imaging experiments, application of the group I mGluR agonists to fura-2-loaded cells elicited increases in intracellular Ca2+ in both the somatic and dendritic regions. The group II (mGluR2/mGluR3) agonist (2 S,3 S,4 S)-α-(carboxycyclopropyl)-glycine (10 μM) and the group III (mGluR4/mGluR6/mGluR7/mGluR8) agonists l(+)-2-amino-4-phosphonobutyric acid (1 mM) and O-phospho-l-serine (200 μM) had no effect on the membrane potential or intracellular Ca2+ levels of the Purkinje neurons. The cultured Purkinje neurons, but not granule neurons or interneurons, showed immunostaining for mGluR1α in both the somatic and dendritic regions. All effects of the group I mGluR agonists were blocked by (+)-α-methyl-4-carboxyphenylglycine (1 mM), an mGluR antagonist. Furthermore, the phospholipase C inhibitor 1-[6-((17β-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-1H-pyrrole-2,5-dione (2 μM) blocked the group I mGluR agonist-mediated electrophysiological response and greatly attenuated the Ca2+ signal elicited by group I mGluR agonists, particularly in the dendrites. The inactive analogue1-[6-((17β-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]2,5-pyrrolidine-dione (2 μM) was relatively ineffective against the electrophysiological response and Ca2+ signal. These results indicate that functional group I mGluRs (but not group II or III mGluRs) can be activated on mature Purkinje neurons in culture and result in changes in neuronal excitability and intracellular Ca2+ mediated through phospholipase C. These data obtained from a defined neuronal type, the Purkinje neuron, confirm biochemical and molecular studies on the transduction mechanisms of group I mGluRs and show that this transduction pathway is linked to neuronal excitability and intracellular Ca2+ release in the Purkinje neurons.

Analysis of voltage-gated and synaptic conductances contributing to network excitability defects in the mutant mouse tottering

1994 ◽  
Vol 71 (1) ◽  
pp. 1-10 ◽  
Author(s):  
S. A. Helekar ◽  
J. L. Noebels
Keyword(s):  
Gabaa Receptor ◽  
Pyramidal Neurons ◽  
Hippocampal Slices ◽  
Channel Blockers ◽  
Gamma Aminobutyric Acid ◽  
Voltage Gated ◽  
Voltage Dependent ◽  
Prolonged Duration ◽  
Ca3 Pyramidal Neurons ◽  
The Difference

1. Intracellular current- and voltage-clamp recordings were carried out in CA3 pyramidal neurons from hippocampal slices of adult tg/tg mice and their coisogenic C57BL/6J (+/+) controls with the use of the single-electrode switch-clamp technique. The principal aim of this study was to investigate the mechanisms responsible for the tg gene-linked prolongation (mean 60%) of a giant synaptic response, the potassium-induced paroxysmal depolarizing shift (PDS) at depolarized membrane potentials (Vm -47 to -54 mV) during synchronous network bursting induced by 10 mM potassium ([K+]o). 2. To examine the role of intrinsic voltage-dependent conductances underlying the mutant PDS prolongation, neurons were voltage clamped by the use of microelectrodes filled with 100 mM QX-314 or QX-222 chloride (voltage-gated sodium channel blockers) and 2 M cesium sulphate (potassium channel blocker). The whole-cell currents active during the PDS showed a significantly prolonged duration (mean 34%) at depolarized Vms in tg/tg compared with +/+ cells, indicating that a defect in voltage-dependent conductances is unlikely to completely account for the mutant phenotype. 3. Bath application of 40 microM (DL)-2-aminophosphonovalerate (DL-APV) produced a 30% reduction in PDS duration in both genotypes but failed to significantly alter the tg gene-linked prolongation compared with the wild type. These data indicate that the mutant PDS abnormality does not result from a selective increase of the N-methyl-D-aspartate (NMDA) receptor-mediated excitatory synaptic component. 4. Blockade of gamma-aminobutyric acid-A (GABAA) transmission with picrotoxin (50 microM) or bicuculline (1–5 microM) completely eliminated the difference in PDS duration between the genotypes. Furthermore, although both GABAA receptor antagonists increased the mean PDS duration in +/+ neurons, they did not significantly alter it in tg/tg neurons. These findings are consistent with a reduction in GABAA receptor-mediated synaptic inhibition during bursting in the tg CA3 hippocampal network. 5. To test this hypothesis, bursting CA3 pyramidal neurons were loaded intracellularly with chloride by the use of KCl-filled microelectrodes to examine the effect of reversing the hyperpolarizing chloride-dependent GABAA receptor-mediated inhibitory postsynaptic component of the PDS. Chloride loading prolonged PDS duration in both genotypes, but the increase was greater in +/+ than in tg/tg neurons, indicating that a smaller GABAA inhibitory postsynaptic potential (IPSP) component was reversed in the mutant.(ABSTRACT TRUNCATED AT 400 WORDS)

Hippocampal pyramidal cells: significance of dendritic ionic conductances for neuronal function and epileptogenesis

1979 ◽  
Vol 42 (2) ◽  
pp. 476-496 ◽  
Author(s):  
R. D. Traub ◽  
R. Llinas
Keyword(s):  
Hot Spots ◽  
Potassium Conductance ◽  
Pyramidal Cells ◽  
Calcium Currents ◽  
Membrane Properties ◽  
Repetitive Firing ◽  
Published Data ◽  
Neuronal Responses ◽  
Voltage Dependent ◽  
Hippocampal Pyramidal Cells

1. Starting with published data derived mainly from hippocampal slice preparations, we have used computer-modeling techniques to study hippocampal pyramidal cells (HPCs). 2. The dendrites of the HPC apparently have a short electrotonic length. Calcium spikes are apparently generated by a voltage-dependent mechanism whose kinetics are slow in comparison with those generating sodium spikes of the soma. Inward calcium currents are assumed to trigger a long-lasting potassium conductance. This slow calcium-potassium system, which in our model is located predominantly on the dendrites, provides a heuristic model to describe the mechanism for a) the after-depolarization following an HPC soma (sodium) spike, b) the long afterhyperpolarization following repetitive firing, c) bursts of spikes that sometimes occur after orthodromic or antidromic stimulation, and d) the buildup of the "depolarizing shift" during the strong synaptic input presumed to occur during seizures. 3. Fast prepotentials or d-spikes are shown to arise most probably from dendritic "hot spots" of sodium-regenerative membrane. The limited amplitude and short duration of these prepotentials imply that the hot spots are located on small dendrites. 4. Dendritic electroresponsiveness, first postulated for the HPC by Spencer and Kandel (52), is analyzed quantitatively here and is shown to provide rich integrative possibilities for this cell. Our model suggests that, for these nerve cells, alterations in specific membrane properties, particularly calcium electroresponsiveness, can lead to bursting behavior that resembles epileptogenic neuronal responses.

Group I mGluRs Increase Excitability of Hippocampal CA1 Pyramidal Neurons by a PLC-Independent Mechanism

2002 ◽  
Vol 88 (1) ◽  
pp. 107-116 ◽  
Author(s):  
David R. Ireland ◽  
Wickliffe C. Abraham
Keyword(s):  
Metabotropic Glutamate Receptors ◽  
Pyramidal Neurons ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Receptor Subtypes ◽  
Ca1 Pyramidal Neurons ◽  
Group I ◽  
Hippocampal Ca1 ◽  
Group I Mglurs ◽  
Induced Changes

Previous studies have implicated phospholipase C (PLC)-linked Group I metabotropic glutamate receptors (mGluRs) in regulating the excitability of hippocampal CA1 pyramidal neurons. We used intracellular recordings from rat hippocampal slices and specific antagonists to examine in more detail the mGluR receptor subtypes and signal transduction mechanisms underlying this effect. Application of the Group I mGluR agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) suppressed slow- and medium-duration afterhyperpolarizations (s- and mAHP) and caused a consequent increase in cell excitability as well as a depolarization of the membrane and an increase in input resistance. Interestingly, with the exception of the suppression of the mAHP, these effects were persistent, and in the case of the sAHP lasting for more than 1 h of drug washout. Preincubation with the specific mGluR5 antagonist, 2-methyl-6-(phenylethynyl)-pyridine (MPEP), reduced but did not completely prevent the effects of DHPG. However, preincubation with both MPEP and the mGluR1 antagonist LY367385 completely prevented the DHPG-induced changes. These results demonstrate that the DHPG-induced changes are mediated partly by mGluR5 and partly by mGluR1. Because Group I mGluRs are linked to PLC via G-protein activation, we also investigated pathways downstream of PLC activation, using chelerythrine and cyclopiazonic acid to block protein kinase C (PKC) and inositol 1,4,5-trisphosphate-(IP3)-activated Ca2+ stores, respectively. Neither inhibitor affected the DHPG-induced suppression of the sAHP or the increase in excitability nor did an inhibitor of PLC itself, U-73122. Taken together, these results argue that in CA1 pyramidal cells in the adult rat, DHPG activates mGluRs of both the mGluR5 and mGluR1 subtypes, causing a long-lasting suppression of the sAHP and a consequent persistent increase in excitability via a PLC-, PKC-, and IP3-independent transduction pathway.

Zn2+ Blocks the NMDA- and Ca2+-Triggered Postexposure Current I pe in Hippocampal Pyramidal Cells

1998 ◽  
Vol 79 (2) ◽  
pp. 1124-1126 ◽  
Author(s):  
Qiang X. Chen ◽  
Katherine L. Perkins ◽  
Robert K. S. Wong
Keyword(s):  
Divalent Cations ◽  
Pyramidal Cells ◽  
Cell Voltage ◽  
Continuous Growth ◽  
Ca1 Pyramidal Cells ◽  
Cation Current ◽  
Hippocampal Ca1 ◽  
Intracellular Ca ◽  
Hippocampal Pyramidal Cells

Chen, Qiang X., Katherine L. Perkins, and Robert K. S. Wong. Zn2+ blocks the NMDA- and Ca2+-triggered postexposure current I pe in hippocampal pyramidal cells. J. Neurophysiol. 79: 1124–1126, 1998. Whole cell voltage-clamp recordings from acutely isolated hippocampal CA1 pyramidal cells from adult guinea pigs were used to evaluate divalent cations as possible blockers of the postexposure current ( I pe). I pe is a cation current that is triggered by the rise in intracellular Ca2+ concentration that occurs after the application of a toxic level of N-methyl-d-aspartate (NMDA). Once triggered, I pe continues to grow until death of the neuron occurs. I pe may be a critical link between transient NMDA exposure and cell death. I pe was blocked by micromolar concentrations of Zn2+. The Zn2+ effect had an IC50 of 64 μM and saturated at 500 μM. Prolonged Zn2+ block of I pe revealed that the maintenance of a steady I pe is not dependent on I pe-mediated Ca2+ influx but that the continuous growth in I pe is dependent on I pe-mediated Ca2+ influx. The availability of an effective blocker of I pe should facilitate the investigation of the intracellular activation pathway of I pe and the role of I pe in neuronal death.

Modulation of Multiple Potassium Currents by Metabotropic Glutamate Receptors in Neurons of the Hypothalamic Supraoptic Nucleus

1997 ◽  
Vol 78 (6) ◽  
pp. 3428-3437 ◽  
Author(s):  
L. A. Schrader ◽  
J. G. Tasker
Keyword(s):  
Glutamate Receptors ◽  
Supraoptic Nucleus ◽  
Metabotropic Glutamate Receptors ◽  
Metabotropic Glutamate Receptor ◽  
Outward Current ◽  
Magnocellular Neurons ◽  
Inward Current ◽  
Voltage Gated ◽  
Metabotropic Glutamate ◽  
Group I

Schrader, L. A. and J. G. Tasker. Modulation of multiple potassium currents by metabotropic glutamate receptors in neurons of the hypothalamic supraoptic nucleus. J. Neurophysiol. 78: 3428–3437, 1997. We studied the effects of activation of the metabotropic glutamate receptors on intrinsic currents of magnocellular neurons of the supraoptic nucleus (SON) with whole cell patch-clamp and conventional intracellular recordings in coronal slices (400 μm) of the rat hypothalamus. Trans-(±)-1-amino-1,3-cyclopentane dicarboxylic acid ( trans-ACPD, 10–100 μM), a broad-spectrum metabotropic glutamate receptor agonist, evoked an inward current (18.7 ± 3.45 pA) or a slow depolarization (7.35 ± 4.73 mV) and a 10–30% decrease in whole cell conductance in ∼50% of the magnocellular neurons recorded at resting membrane potential. The decrease in conductance and the inward current were caused largely by the attenuation of a resting potassium conductance because they were reduced by the replacement of intracellular potassium with an equimolar concentration of cesium or by the addition of potassium channel blockers to the extracellular medium. In some cells, trans-ACPD still elicited a small inward current after blockade of potassium currents, which was abolished by the calcium channel blocker, CdCl2. Trans-ACPD also reduced voltage-gated and Ca2+-activated K+ currents in these cells. Trans-ACPD reduced the transient outward current ( I A) by 20–70% and/or the I A-mediated delay to spike generation in ∼60% of magnocellular neurons tested. The cells that showed a reduction of I A generally also showed a 20–60% reduction in a voltage-gated, sustained outward current. Finally, trans-ACPD attenuated the Ca2+-dependent outward current responsible for the afterhyperpolarization ( I AHP) in ∼60% of cells tested. This often revealed an underlying inward current thought to be responsible for the depolarizing afterpotential seen in some magnocellular neurons. (RS)-3,5-dihydroxyphenylglycine, a group I receptor-selective agonist, mimicked the effects of trans-ACPD on the resting and voltage-gated K+ currents. (RS)-α-methyl-4-carboxyphenylglycine, a group I/II metabotropic glutamate receptor antagonist, blocked these effects. A group II receptor agonist, 2S,1′S,2′S-2carboxycyclopropylglycine and a group III receptor agonist, l(+)-2-amino-4-phosphonobutyric acid, had no effect on the resting or voltage-gated K+ currents, indicating that the reduction of K+ currents was mediated by group I receptors. About 80% of the SON cells that were labeled immunohistochemically for vasopressin responded to metabotropic glutamate receptor activation, whereas only 33% of labeled oxytocin cells responded, suggesting that metabotropic receptors are expressed preferentially in vasopressinergic neurons. These data indicate that activation of the group I metabotropic glutamate receptors leads to an increase in the postsynaptic excitability of magnocellular neurons by blocking resting K+ currents as well as by reducing voltage-gated and Ca2+-activated K+ currents.

Inhibition of Na+/H+exchange stimulates CCK secretion in STC-1 cells

1998 ◽  
Vol 275 (4) ◽  
pp. G689-G695
Author(s):  
Veronica Prpic ◽  
J. Gregory Fitz ◽  
Yu Wang ◽  
John R. Raymond ◽  
Maria N. Garnovskaya ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Cell Metabolism ◽  
Hormone Secretion ◽  
Membrane Depolarization ◽  
Ph Sensitive ◽  
Extracellular Medium ◽  
Voltage Dependent ◽  
Effects Of Ph ◽  
Intracellular Ca ◽  
Cck Release

It has been demonstrated that K+ channel regulation of membrane potential is critical for control of CCK secretion. Because certain K+ channels are pH sensitive, it was postulated that pH affects K+channel activity in the CCK-secreting cell line STC-1 and may participate in regulating CCK secretion. The present study examines the role of electroneutral Na+/H+exchange on extracellular acidification and hormone secretion. Treatment of STC-1 cells with the amiloride analog ethylisopropyl amiloride (EIPA) to inhibit Na+/H+exchange inhibited Na+-dependent H+ efflux and increased basal CCK secretion. Substituting choline for NaCl in the extracellular medium elevated basal intracellular Ca2+concentration and stimulated CCK release. Stimulatory effects on hormone secretion were blocked by the L-type Ca2+ channel blocker diltiazem, indicating that secretion was dependent on the influx of extracellular Ca2+. To determine whether the effects of EIPA and Na+ depletion were due to membrane depolarization, we tested graded KCl concentrations. The ability of EIPA to increase CCK secretion was inhibited by depolarization induced by 10–50 mM KCl in the bath. Maneuvers to lower intracellular pH (pHi), including reducing extracellular pH (pHo) to 7.0 or treatment with sodium butyrate, significantly increased CCK secretion. To examine whether pH directly affects membrane K+ permeability, we measured outward currents carried by K+, using whole cell patch techniques. K+ current was significantly inhibited by lowering pHo to 7.0. These effects appear to be mediated through changes in pHi, because intracellular dialysis with acidic solutions nearly eliminated current activity. These results suggest that Na+/H+exchange and membrane potential may be functionally linked, where inhibition of Na+/H+exchange lowers pHi and depolarizes the membrane, perhaps through inhibition of pH-sensitive K+ channels. In turn, K+ channel closure and membrane depolarization open voltage-dependent Ca2+ channels, leading to an increase in cytosolic Ca2+ and CCK release. The effects of pHi on K+ channels may serve as a potent stimulus for hormone secretion, linking cell metabolism and secretory functions.

Bombesin-evoked gastrin release and calcium signaling in human antral G cells in culture

1999 ◽  
Vol 276 (1) ◽  
pp. G227-G237 ◽  
Author(s):  
Paul E. Squires ◽  
R. Mark Meloche ◽  
Alison M. J. Buchan
Keyword(s):  
Cell Culture ◽  
Calcium Signaling ◽  
Gastrin Release ◽  
Voltage Gated ◽  
Gastrin Releasing Peptide ◽  
G Cells ◽  
Peptide Family ◽  
Inositol 1,4,5 Trisphosphate ◽  
Voltage Dependent ◽  
Intracellular Ca

Amplification of mRNA from a human antral cell culture preparation demonstrated the presence of two receptors of the bombesin and gastrin-releasing peptide family, GRPR-1 and BRS-3. Single cell microfluorometry demonstrated that most cells that exhibited bombesin-evoked changes in intracellular Ca2+ concentration were gastrin immunoreactive, indicating that antral G cells express the GRPR subtype. There were two components to the intracellular Ca2+ response: an initial nitrendipine-insensitive mobilization followed by a sustained phase that was inhibited by removal of extracellular Ca2+ and 20 mM caffeine and was partially inhibited by 10 μM nitrendipine. Preexposure of cells to thapsigargin and caffeine prevented the response to bombesin, indicating activation of inositol 1,4,5-trisphosphate (IP3)-sensitive stores. Gastrin release could be partially reversed by removal of extracellular Ca2+ and blockade of L-type voltage-dependent Ca2+ channels, indicating that a component of the secretory response to bombesin was dependent on Ca2+ influx. These data demonstrated that bombesin-stimulated gastrin release from human antral G cells resulted from activation of GRPRs and involved both release of intracellular Ca2+ and influx of extracellular Ca2+through a combination of L-type voltage-gated and IP3-gated Ca2+ channels.

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