High- and low-threshold calcium currents in neurons acutely isolated from rat sensorimotor cortex

1990 ◽  
Vol 120 (2) ◽  
pp. 175-178 ◽  
Author(s):  
R.J. Sayer ◽  
P.C. Schwindt ◽  
W.E. Crill
Keyword(s):  
Sensorimotor Cortex ◽  
Calcium Currents ◽  
Low Threshold

Protein kinase activator 1-oleoyl-2-acetyl-sn-glycerol inhibits two types of calcium currents in GH3 cells

1988 ◽  
Vol 254 (1) ◽  
pp. C206-C210 ◽  
Author(s):  
C. Marchetti ◽  
A. M. Brown
Keyword(s):  
Protein Kinase ◽  
Chick Embryo ◽  
Calcium Currents ◽  
Gh3 Cells ◽  
High Threshold ◽  
Pituitary Cells ◽  
Excitable Cells ◽  
Whole Cell ◽  
Whole Cell Patch Clamp ◽  
Low Threshold

Two types of Ca2+ currents, high-threshold, long-lasting, or L currents and low-threshold, transient, or T currents, are present in many excitable cells. L-type Ca2+ current is modulated by, among others, beta- and alpha-adrenoreceptors and intracellular Ca2+, but modulation of T-type Ca2+ current is less well established. 1-Oleoyl-2-acetyl-sn-glycerol (OAG), a synthetic activator of protein kinase C (PKC), modulates whole cell Ca2+ currents in a variety of excitable cells. Whether activators of PKC affect preferentially L and T types of Ca2+ currents is unknown. We tested OAGs effects on whole cell Ca2+ currents in the clonal GH3 line of anterior pituitary cells. The currents were measured using the whole cell patch-clamp method. Four to 60 microM OAG reversibly reduced Ca2+ currents produced by test potentials to 10 mV, and the inhibition was half maximal at approximately 25 microM. Such concentrations depress Ca2+ currents in chick embryo dorsal root ganglion (DRG) cells and clonal AtT-20 pituitary cells. To test whether OAG acted preferentially on L or T current, we separated the two using depolarizing prepulses to inactivate T current. OAG (40 microM) attenuated T currents by 60% and L currents by 50%. The current waveforms were not changed and were simply scaled, and the effects on both occurred approximately 15 s after OAG was applied. In chick embryo DRGs OAG inhibited the T current by 30% and the L current by 50%. We conclude that PKC modulates Ca2+ currents by acting on both L and T Ca2+ channels.

Low- and high-voltage-activated calcium currents in rat spinal dorsal horn neurons

1990 ◽  
Vol 63 (2) ◽  
pp. 273-285 ◽  
Author(s):  
P. D. Ryu ◽  
M. Randic
Keyword(s):  
Dorsal Horn ◽  
High Voltage ◽  
Calcium Current ◽  
Spinal Dorsal Horn ◽  
Calcium Currents ◽  
High Threshold ◽  
Dorsal Horn Neurons ◽  
Spinal Dorsal ◽  
Low Threshold ◽  
Spinal Dorsal Horn Neurons

1. Calcium currents in immature rat spinal dorsal horn neurons in transverse slices were studied with the single-electrode voltage-clamp technique. Using experimental conditions that minimized voltage-dependent Na+ and K+ currents, we distinguished low- and high-voltage-activated calcium currents on the basis of their voltage dependence and sensitivity to the Ca2(+)-channel agonist and antagonist drugs. 2. The low-voltage-activated transient calcium current is evoked with weak depolarizing voltage commands. It begins to activate at potentials positive to -70 mV and increases in amplitude and rate of decay with depolarization, the peak values being reached between -40 and -30 mV. The current is fully activated at a holding potential of about -110 mV. Steady-state inactivation is complete at potentials in the range of -60 to -50 mV. 3. The transient component of the high-threshold calcium current appears at membrane potentials close to -40 mV and slowly decays within several hundreds of milliseconds. The amplitude of the current increases with more negative holding potentials (-100 to -40 mV). 4. The sustained component of the high-threshold calcium current seems to activate at potentials positive to -40 mV and exhibits little inactivation during 0.3- to 0.5-s depolarizing commands. This component is better isolated at more depolarized holding potentials (between -40 and -30 mV) that inactivate the transient components of the low- and high-threshold calcium currents. 5. A rundown of calcium currents was seen in dorsal horn cells. The time stability of the transient and sustained components of the high-threshold calcium current was lower than that of the low-threshold transient current. The latter current seemed to be insensitive up to 1 h. 6. (-)-Bay K 8644 (1-10 microM), a dihydropyridine agonist, enhanced the high-threshold calcium current, in particular the sustained component, but not the transient low-threshold calcium current. The dihydropyridine antagonist nifedipine (5-50 microM) selectively reduced the sustained component of the high-threshold calcium current while having little or no effect on the transient components of the low- and high-threshold calcium currents. 7. Cadmium ions (60-100 microM) and cobalt ions (2 mM) markedly reduced both components of the high-threshold calcium current, and Cd2+ only slightly decreased the low-threshold transient current. However, all three components are indiscriminately blocked by higher concentrations of Cd2+ and Co2+.(ABSTRACT TRUNCATED AT 400 WORDS)

Transient enhancement of low-threshold calcium current in thalamic relay neurons after corticectomy

1993 ◽  
Vol 70 (1) ◽  
pp. 20-27 ◽  
Author(s):  
J. M. Chung ◽  
J. R. Huguenard ◽  
D. A. Prince
Keyword(s):  
Calcium Currents ◽  
High Threshold ◽  
Pharmacological Properties ◽  
Current Time ◽  
Cortical Ablation ◽  
Thalamic Relay ◽  
Low Threshold ◽  
Small Change ◽  
Thalamic Relay Neurons ◽  
Relay Neurons

1. The alterations of voltage-sensitive calcium currents produced in thalamic cells by injury were investigated under voltage clamp using patch-clamp recordings in the whole-cell configuration. 2. One day after unilateral cortical ablation in immature rats (postnatal day 7), low-threshold transient calcium (T) currents in acutely isolated thalamic relay neurons (RNs) were increased by 68% compared with contralateral controls (P < 0.001). Three days after the operation, T currents in injured neurons were at 44% of control levels (P < 0.001). On the other hand, high-threshold (L) calcium currents in RNs did not change over the same interval. 3. To investigate the mechanism for the increase of T current, both kinetics and voltage dependency of activation and inactivation were examined. At a test voltage of -40 mV, the activation time constant decreased from 4.1 to 3.2 ms (P < 0.05); however, this small change was insufficient to explain the large increase in T current. Time constants for both fast and slow inactivation did not change significantly, nor did voltage dependence of activation or inactivation of thalamic T currents. 4. Methyl-phenyl-succinimide (MPS, 1 mM), a compound known to block T currents, was used to examine possible alterations in the pharmacological properties of T channels after injury. MPS was more effective in reducing T currents in normal versus injured RNs (24 and 20% reductions, respectively; P < 0.05), suggesting that pharmacological properties of T channels in the injured RNs may be different from those of the normal RNs.(ABSTRACT TRUNCATED AT 250 WORDS)

The modulation of sensory transmission through the medullary dorsal horn during cortically driven mastication

1986 ◽  
Vol 64 (7) ◽  
pp. 999-1005 ◽  
Author(s):  
Joong Soo Kim ◽  
M. Catherine Bushnell ◽  
Gary H. Duncan ◽  
James P. Lund
Keyword(s):  
Dorsal Horn ◽  
Unit Activity ◽  
Sensorimotor Cortex ◽  
Dynamic Range ◽  
Cortical Stimulation ◽  
Motor Nucleus ◽  
Trigeminal Motor Nucleus ◽  
Sensory Transmission ◽  
Medullary Dorsal Horn ◽  
Low Threshold

During mastication, reflexes are modulated and sensory transmission is altered in interneurons and ascending pathways of the rostral trigeminal sensory complex. The current experiment examines the modulation of sensory transmission through the most caudal part of the trigeminal sensory system, the medullary dorsal horn, during fictive mastication produced by cortical stimulation. Extracellular single unit activity was recorded from the medullary dorsal horn, and multiple unit activity was recorded from the trigeminal motor nucleus in anesthetized, paralyzed rabbits. The masticatory area of sensorimotor cortex was stimulated to produce rhythmic activity in the trigeminal motor nucleus (fictive mastication). Activity in the dorsal horn was compared in the presence and absence of cortical stimulation. Fifty-two percent of neurons classified as low threshold and 83% of neurons receiving noxious inputs were influenced by cortical stimulation. The cortical effects were mainly inhibitory, but 21% of wide dynamic range and 6% of low threshold cells were excited by cortical stimulation. The modulation produced by cortical stimulation, whether inhibitory or excitatory, was not phasically related to the masticatory cycle. It is likely that, when masticatory movements are commanded by the sensorimotor cortex, the program includes tonic changes in sensory transmission through the medullary dorsal horn.

Calcium currents of cardiovascular neurons isolated from adult guinea pigs

1987 ◽  
Vol 252 (4) ◽  
pp. H867-H871
Author(s):  
D. L. Kunze
Keyword(s):  
Guinea Pigs ◽  
Action Potentials ◽  
Calcium Current ◽  
Threshold Current ◽  
Bipolar Cells ◽  
Calcium Currents ◽  
High Threshold ◽  
Calcium Dependent ◽  
Low Threshold ◽  
Patch Technique

A preparation of cells isolated from the medial and dorsal nuclei of the solitary tract of the medulla of adult guinea pigs was developed to examine the electrical properties of neurons isolated from an area of the central nervous system which is involved in the control of arterial pressure and heart rate. Bipolar cells of approximately 10 microns diameter were obtained on enzymatic dispersion. The cells were studied with the use of the patch technique for whole cell recording. Action potentials were elicited by depolarizing pulses in the presence of 10(-5) M tetrodotoxin which blocked a sodium-dependent current. These action potentials were calcium dependent and were eliminated by adding 1 mM Cd to the bath. In all cells studied, two voltage-dependent components to the calcium current were identified. In 10 mM Ca a high-threshold component activated at approximately -20 mV from holding potentials of -30 mV. A second lower threshold component was activated at -40 mV from more negative holding potentials of -80 mV. The low-threshold component was rapidly inactivating, whereas the high-threshold current slowly inactivated. The peak amplitudes of the two components were similar. Both components were blocked by 1 mM Cd. A role for the low-threshold calcium current in generating repetitive activity is postulated.

Calcium currents in acutely isolated human neocortical neurons

1993 ◽  
Vol 69 (5) ◽  
pp. 1596-1606 ◽  
Author(s):  
R. J. Sayer ◽  
A. M. Brown ◽  
P. C. Schwindt ◽  
W. E. Crill
Keyword(s):  
Pyramidal Neurons ◽  
Intractable Epilepsy ◽  
Pyramidal Cells ◽  
Cell Voltage ◽  
Threshold Current ◽  
Calcium Currents ◽  
High Threshold ◽  
Peak Current ◽  
Neocortical Neurons ◽  
Low Threshold

1. Ca2+ currents were investigated in neurons acutely isolated from adult human temporal neocortex. The aim was to compare the basic characteristics of the currents with those previously described in animals and to examine the effects of dihydropyridine Ca2+ antagonists and antiepileptic drugs. The tissue, obtained from patients undergoing temporal lobe surgery for medically intractable epilepsy, was sliced, incubated in papain, and triturated. 2. Most of the isolated neurons (34 of 36) were judged to be pyramidal cells by their morphology. Whole-cell voltage-clamp recordings revealed two components of Ca2+ current: 1) a low-threshold (T-type) current that was transient, small in amplitude, and required hyperpolarization more negative than -70 mV for removal of inactivation and 2) a high-threshold current that was slowly inactivating and was available for activation from more positive potentials. The characteristics of the Ca2+ currents were very similar to those in the neocortical neurons of young rats, although the low-threshold current was less prominent in the human cells. 3. Subcomponents of the high-threshold current were identified by pharmacology. About 20% of the peak current was blocked by omega-conotoxin GVIA (presumed N current) and 40-50% of the peak current was blocked by micromolar concentrations of the dihydropyridine Ca2+ antagonists nifedipine and nimodipine (presumed L current). In two neurons tested with a range of nimodipine concentrations, the threshold for suppression of the high-threshold current was approximately 10 nM. 4. The antiepileptic agents ethosuximide, carbamazepine, and valproate did not affect the Ca2+ currents at therapeutically relevant concentrations. Phenytoin marginally reduced the low- and high-threshold Ca2+ currents at 8 microM (a concentration corresponding to the upper therapeutic range). The results do not support the hypothesis that inhibition of Ca2+ currents in neocortical pyramidal neurons is a major action of these drugs.

Calcium current and inactivation in identified neurons in Hermissenda crassicornis

1994 ◽  
Vol 72 (5) ◽  
pp. 2196-2208 ◽  
Author(s):  
E. N. Yamoah ◽  
A. M. Kuzirian ◽  
J. V. Sanchez-Andres
Keyword(s):  
Time Course ◽  
Threshold Current ◽  
Calcium Currents ◽  
Identified Neurons ◽  
Tetraacetic Acid ◽  
Activation Kinetics ◽  
Inactivation Curve ◽  
Na Currents ◽  
Slope Factor ◽  
Low Threshold

1. N-type (omega-conotoxin sensitive) calcium currents (ICa) were recorded in identified neurons in Hermissenda crassicornis using low-resistance patch electrodes (0.7 +/- 0.3 M omega; n = 101) under conditions that eliminated inward Na+ currents (choline ions substitution) and suppressed outward K+ currents (Cs+, tetraethylammonium, and 4-AP). Step depolarization from a holding potential of -60 mV to potentials above -30 mV elicited ICa, which peaked approximately 20 mV and declined with increasing depolarizations. 2. Evidence for a low-threshold current was present. Step depolarization from a more hyperpolarizing potentials (e.g., -90 mV) revealed a small shoulder (< 100 pA) at -60 to -40 mV that was sensitive to Co2+ and Ni2+. However, under the conditions examined here (holding potential of -60 mV), the high-voltage-activated current predominated. 3. Barium (Ba2+) and strontium (Sr2+) permeate the Ca2+ channel with similar activation kinetics (ease of permeation; Ba2+ > Ca2+ > Sr2+). Steady-state activation of permeability versus membrane potentials for Ca2+, Ba2+, and Sr2+ as charge carriers could be fitted with the Boltzmann equation, with half-activation voltage and slope factor of 2.9 and 7.7 mV for ICa, -13.1 mV and 7.8 for Ba2+ current (IBa) and -2.3 mV and 7.8 for Sr2+ current (ISr). The time course of activation was monotonic with time constant (tau) for ICa ranging from 2 to 8 ms. 4. The inactivation profile was complex. At negative step potentials (e.g., -20 mV), inactivation of the current was slow. Depolarization steps to relatively positive voltages (e.g., 10 mV) showed more rapid inactivation than those at more positive potentials (e.g., 40 mV). When extracellular Ca2+ was raised from 5 to 10 mM, a biphasic decay (tau fast of 25 +/- 4 ms; and tau slow of 473 +/- 64 ms; mean +/- SD, n = 9) was seen. Such an observation suggested a current-mediated inactivation. 5. With a pulse duration of approximately 350 ms, ISr showed inactivation whereas Ba2+ virtually removed the decay. However, IBa turned off with more prolonged depolarization. 6. A twin-pulse protocol was used to assess the voltage dependence of inactivation: an incomplete U-shaped inactivation curve was observed for ICa, IBa, and ISr. Channels available for inactivation were increased in the presence of Ca2+ ions. 7. Inactivation was further studied with the Ca2+ chelators, ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid and bis(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA). With 10 mM of BAPTA, in the pipette, inactivation was reduced but not removed.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of Voltage-Activated Calcium Currents by Mechanical Stimulation in Rat Sensory Neurons

1998 ◽  
Vol 80 (4) ◽  
pp. 1647-1652 ◽  
Author(s):  
Yona Bouskila ◽  
Hugh Bostock
Keyword(s):  
Action Potential ◽  
Sensory Neurons ◽  
Mechanical Stimulation ◽  
Action Potential Duration ◽  
Calcium Currents ◽  
Dorsal Root Ganglion Neurons ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Low Threshold ◽  
Ganglion Neurons

Bouskila, Yona and Hugh Bostock. Modulation of voltage-activated calcium currents by mechanical stimulation in rat sensory neurons. J. Neurophysiol. 80: 1647–1652, 1998. We examined the effects of mechanical stress, induced by a stream of bath solution, on evoked action potentials, electrical excitability, and Ca2+ currents in rat dorsal root ganglion neurons in culture with the use of the whole cell patch-clamp technique. Action-potential duration was altered reversibly by flow in 39% of the 51 neurons tested, but membrane potential and excitability were unaffected. The flow-induced increases and decreases in action-potential duration were consistent with the different effects of flow on two types of Ca2+ channel, determined by voltage-clamp recordings of Ba2+ currents. Current through ω-conotoxin–sensitive (N-type) Ca2+ channels increased by an estimated 74% with flow, corresponding to 23% increase in the total high voltage–activated current, whereas current through low-threshold voltage-activated (T-type) channels decreased by 14%. We conclude that modulation of voltage-activated Ca2+ currents constitutes a route by which mechanical events can regulate Ca2+ influx in sensory neurons.

Area postrema voltage-activated calcium currents

1996 ◽  
Vol 75 (1) ◽  
pp. 133-141 ◽  
Author(s):  
M. Hay ◽  
E. M. Hasser ◽  
K. A. Lindsley
Keyword(s):  
Threshold Voltage ◽  
Area Postrema ◽  
Threshold Current ◽  
Calcium Currents ◽  
High Threshold ◽  
Patch Clamp Technique ◽  
Experimental Conditions ◽  
Nickel Ions ◽  
Transient Component ◽  
Low Threshold

1. Calcium currents in rabbit area postrema neurons were studied with the perforated patch-clamp technique. Experimental conditions eliminated Na+ and K+ currents and identified both low- and high-threshold voltage-activated calcium currents. 2. Low-threshold, T-type calcium currents were observed in 64% of the area postrema neurons recorded. This current activated near -60 mV and had an average peak amplitude of -36.2 +/- 5 pA (mean +/- SE) at -40 mV. This current began rapid inactivation near -95 mV, reached half-maximal inactivation at -71 mV and was totally inactivated by -40 mV. 3. A high-threshold transient current was recorded in all area postrema neurons, which consisted of both a transient and sustained component. This current was present at voltages greater than -40 mV and the transient component of this current was responsible for the majority of the total Ca2+ current. 4. Nickel ions (10 microM) effectively reduced both the T-type current and the high-threshold current. Cadmium ions (100 microM) effectively reduced the high-threshold current while having insignificant effects on the low-threshold current. 5. Application of the dihydropyridine antagonist nimodipine (1-10 microM) had no effect on either the low- or high-threshold voltage-activated calcium Ca2+ in area postrema neurons. In addition, application of omega-conotoxin-GVIA (2-10 microM) was also without effect on either the low- or high-threshold voltage-activated Ca2+ current, suggesting that area postrema neurons possess neither L- or N-type voltage-activated Ca2+ currents. 6. Application of omega-conotoxin MVIIC (10 microM) significantly inhibited the peak high-threshold Ca2+ current by 65.4% suggesting that area postrema neurons do possess a omega-conotoxin MVIIC-sensitive high-threshold Ca2+ channel. 7. Arg-vasopressin (150 nM) significantly increased the transient component of the high-threshold Ca2+ current but had little effect on either the low-threshold or the high-threshold sustained component.

Stimulatory effect of ouabain on T- and L-type calcium currents in guinea pig cardiac myocytes

1990 ◽  
Vol 258 (5) ◽  
pp. H1620-H1623 ◽  
Author(s):  
B. Le Grand ◽  
E. Deroubaix ◽  
A. Coulombe ◽  
E. Coraboeuf
Keyword(s):  
Steady State ◽  
Guinea Pig ◽  
Ventricular Myocytes ◽  
Calcium Currents ◽  
High Threshold ◽  
Inactivation Curve ◽  
Cell Recording ◽  
Steady State Inactivation ◽  
Low Threshold ◽  
Free Media

The effect of 10(-6) M ouabain on macroscopic low-threshold T-type Ca2+ and high-threshold L-type Ca2+ currents was studied by whole cell recording in isolated guinea pig ventricular myocytes superfused with K-free, Na-free media, i.e., after suppression of Na-K-ATPase activity and Na influx through the Na-Ca exchanger. Under such conditions, the amplitudes of the two currents were significantly increased by ouabain. In particular, the current occurring in the -50 to -20 mV range (T-type Ca2+) was increased two- to threefold by ouabain and suppressed by 40 microM Ni2+. Ouabain shifted by approximately 10 mV toward negative potentials the steady-state inactivation curve of the T-type Ca2+ current but not that of the L-type Ca2+ current. It is concluded that ouabain enhances not only L-type Ca2+ current but also T-type Ca2+ current possibly through different mechanisms.

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