Low-Threshold L-type Calcium Channels in Rat Dopamine Neurons

2004 ◽  
Vol 91 (3) ◽  
pp. 1450-1454 ◽  
Author(s):  
P. Durante ◽  
C. G. Cardenas ◽  
J. A. Whittaker ◽  
S. T. Kitai ◽  
R. S. Scroggs
Keyword(s):  
Ganglion Cells ◽  
Oscillatory Potentials ◽  
Dopamine Neurons ◽  
Substantia Nigra Pars Compacta ◽  
Whole Cell ◽  
Voltage Range ◽  
Channel Current ◽  
Whole Cell Patch Clamp ◽  
P Type ◽  
Dorsal Root Ganglion Cells

Ca2+ channel subtypes expressed by dopaminergic (DA) neurons in the substantia nigra pars compacta (SNc) were studied using whole cell patch-clamp recordings and blockers selective for different channel types (L, N, and P/Q). Nimodipine (Nim, 2 μM), ω-conotoxin GVIA (Ctx, 1 μM), or ω-agatoxin IVA (Atx, 50 nM) blocked 27, 36, and 37% of peak whole cell Ca2+ channel current, respectively, indicating the presence of L-, N-, and P-type channels. Nim blocked approximately twice as much Ca2+ channel current near activation threshold compared with Ctx or Atx, suggesting that small depolarizations preferentially opened L-type versus N- or P-type Ca2+ channels. N- and L-channels in DA neurons opened over a significantly more negative voltage range than those in rat dorsal root ganglion cells, recorded from using identical conditions. These data provide an explanation as to why Ca2+-dependent spontaneous oscillatory potentials and rhythmic firing in DA neurons are blocked by L-channel but not N-channel antagonists and suggest that pharmacologically similar Ca2+ channels may exhibit different thresholds for activation in different types of neurons.

Delayed rectification in single cells isolated from guinea pig sinoatrial node

1992 ◽  
Vol 262 (3) ◽  
pp. H921-H925 ◽  
Author(s):  
J. M. Anumonwo ◽  
L. C. Freeman ◽  
W. M. Kwok ◽  
R. S. Kass
Keyword(s):  
Guinea Pig ◽  
Sinoatrial Node ◽  
Single Cells ◽  
Equilibrium Potential ◽  
Delayed Rectifier ◽  
Experimental Conditions ◽  
Whole Cell ◽  
Voltage Range ◽  
Whole Cell Patch Clamp ◽  
Delayed Rectification

We have studied delayed rectifier K+ currents (IK) in cells isolated from the sinoatrial node (SAN) region of the guinea pig. Using whole cell patch-clamp procedures, we measured the voltage dependence of IK activation and IK kinetics and the IK equilibrium potential in 4.8 mM extracellular K concentration solutions. Experiments were designed to contrast properties of guinea pig SAN IK with those of IK recorded from SAN cells of the rabbit. We find that guinea pig SAN IK differs from IK recorded from single rabbit SAN cells in its activation threshold, and in the absence of inactivation of whole cell currents recorded over a wide voltage range. These results, along with the relative insensitivity of guinea pig SAN IK to E-4031 and lanthanum, suggest that under our experimental conditions, a strongly rectifying IK component (IK,r) is not the major component of delayed rectification in the guinea pig SAN, as it appears to be in SAN cells of the rabbit.

Possible contribution of long open state to noninactivating Ca2+ current in detrusor cells

1995 ◽  
Vol 269 (1) ◽  
pp. C48-C54 ◽  
Author(s):  
S. Nakayama ◽  
A. F. Brading
Keyword(s):  
Smooth Muscles ◽  
Activation Parameters ◽  
Patch Clamp Technique ◽  
Inactivation Curve ◽  
Voltage Range ◽  
Channel Current ◽  
Whole Cell Patch Clamp ◽  
Dependent Inactivation ◽  
Window Current ◽  
Isolated Smooth Muscle Cells

The whole cell patch-clamp technique was used to measure Ca2+ current in isolated smooth muscle cells from guinea pig urinary bladder. Noniactivating Ca2+ channel current was modeled incorporating the long open state of the Ca2+ channel. When inactivation was examined over a wide voltage range, a completely U-shaped curve was obtained. Lack of inactivation at +80 mV could be attributed to the long open state induced by large depolarization as well as to minimal Ca2+ influx and Ca(2+)-dependent inactivation. Activation parameters were obtained by comparing the amplitudes of conditioned (by +80 mV, 5 s) and unconditioned test potentials. With the use of the activation curve and the U-shaped inactivation curve, a noninactivating current that peaks around +20 mV was obtained. This current is composed of a so-called “window” current and a persistent current brought about by the long open state. Differences in the voltage dependence of the development of the long open state in various smooth muscles, as well as differences in the equilibrium constant between open and inactivated states, could underlie the different patterns of contractile behavior that characterize smooth muscles.

Calcium Currents in Retrogradely Labeled Pyramidal Cells From Rat Sensorimotor Cortex

2000 ◽  
Vol 83 (4) ◽  
pp. 2349-2354 ◽  
Author(s):  
Ansalan Stewart ◽  
Robert C. Foehring
Keyword(s):  
Pyramidal Neurons ◽  
Pyramidal Cells ◽  
Cell Types ◽  
Calcium Currents ◽  
Patch Clamp Technique ◽  
Whole Cell ◽  
Multiple Populations ◽  
Whole Cell Patch Clamp ◽  
The Mean ◽  
P Type

Our previous studies of calcium (Ca2+) currents in cortical pyramidal cells revealed that the percentage contribution of each Ca2+ current type to the whole cell Ca2+ current varies from cell to cell. The extent to which these currents are modulated by neurotransmitters is also variable. This study was directed at testing the hypothesis that a major source of this variability is recording from multiple populations of pyramidal cells. We used the whole cell patch-clamp technique to record from dissociated corticocortical, corticostriatal, and corticotectal projecting pyramidal cells. There were significant differences between the three pyramidal cell types in the mean percentage of L-, P-, and N-type Ca2+ currents. For both N- and P-type currents, the range of percentages expressed was small for corticostriatal and corticotectal cells as compared with cells which project to the corpus callosum or to the general population. The variance was significantly different between cell types for N- and P-type currents. These results suggest that an important source of the variability in the proportions of Ca2+ current types present in neocortical pyramidal neurons is recording from multiple populations of pyramidal cells.

Dihydropyridine- and Neurotoxin-Sensitive and -Insensitive Calcium Currents in Acutely Dissociated Neurons of the Rat Central Amygdala

1997 ◽  
Vol 77 (2) ◽  
pp. 690-701 ◽  
Author(s):  
Baojian Yu ◽  
Patricia Shinnick-Gallagher
Keyword(s):  
Calcium Current ◽  
Calcium Currents ◽  
Similar Proportion ◽  
Central Amygdala ◽  
Patch Clamp Recording ◽  
Whole Cell ◽  
Whole Cell Patch Clamp ◽  
Moderate Rate ◽  
Rate Of Decay ◽  
P Type

Yu, Baojian and Patricia Shinnick-Gallagher. Dihydropyridine- and neurotoxin-sensitive and -insensitive calcium currents in acutely dissociated neurons of the rat central amygdala. J. Neurophysiol. 77: 690–701, 1997. The central amygdala (CeA) is an area involved in emotional learning and stress, and identification of Ca2+ currents is essential to understanding interneuronal communication through this nucleus. The purpose of this study was to separate and characterize dihydropyridine (DHP)- and neurotoxin-sensitive and -resistant components of the whole cell Ca2+ current ( I Ca) in acutely dissociated rat CeA neurons with the use of whole cell patch-clamp recording. Saturating concentrations of nimodipine (NIM, 5 μM), a DHP antagonist, blocked 22% of I Ca; this NIM-sensitive (L-type) current was recorded in 68% of CeA neurons. The DHP agonist Bay K 8644 (5 μM) produced a 36% increase in I Ca in a similar proportion of CeA neurons (70%). ω-Conotoxin GVIA (CgTx GVIA, 1 μM) in saturating concentrations inhibited 30% of I Ca, whereas ω-agatoxin IVA (Aga IVA, 100 nM), in concentrations known to block P-type currents, did not affect I Ca. Higher concentrations of Aga IVA (1 μM) alone reduced I Ca by 34%, but in the presence of NIM (5 μM) and CgTx GVIA (1 μM) blocked only 18% of I Ca. ω-Conotoxin MVIIC (CgTx MVIIC, 250 nM) reduced I Ca by 13% in the presence of CgTx GVIA (1 μM). Application of NIM (5 mM), CgTx GVIA (1 μM), and Aga IVA (1 μM) blocked ∼67% of I Ca. A similar portion (63%) of Ca2+ current was blocked with CgTx MVIIC (250 nM) in the presence of NIM (5 μM) and CgTx GVIA (1 μM). The current resistant to NIM and the neurotoxins represented 37% of I Ca, whereas in neurons not having L-type currents the resistant current made up ∼53% of I Ca (49 ± 2%, mean ± SE). The resistant current activated at around −40 mV and peaked at ∼0 mV with half-activation and -inactivation potentials of −17 and −58 mV and slopes for activation and inactivation of −5 and 13 mV, respectively. The resistant current was sensitive to Cd2+ (IC50 = 2.5 μM) and Ni2+ (IC50 = 86 μM), was larger in Ca2+ than in Ba2+ (ratio = 1.31:1), and showed a moderate rate of decay. In summary, our results show that the high-voltage-activated calcium current in rat CeA neurons is composed of at least four pharmacologically distinct components: L-type current (NIM sensitive, 22%), N-type current (CgTx GVIA sensitive, 30%), Q-type current [Aga IVA (1 μM) and CgTx MVIIC sensitive, ∼13–18%], and a resistant current (Non-L, -N, and -Q current, 33 ∼ 37%), amounting to 37–53% of the total current. The resistant current has some electrophysiological and pharmacological characteristics in common with doe-1, α1E, and R-type calcium currents, but remains unclassified.

scholarly journals Modulation of Calcium Channels in Human Erythroblasts by Erythropoietin

Blood ◽  
1997 ◽  
Vol 89 (1) ◽  
pp. 92-100 ◽  
Author(s):  
Joseph Y. Cheung ◽  
Xue-Qian Zhang ◽  
Krister Bokvist ◽  
Douglas L. Tillotson ◽  
Barbara A. Miller
Keyword(s):  
Single Channel ◽  
Reversal Potential ◽  
Erythropoietin Receptor ◽  
Single Channels ◽  
Open Probability ◽  
Whole Cell ◽  
Voltage Range ◽  
Whole Cell Patch Clamp ◽  
Open Time ◽  
High Doses

Abstract Erythropoietin (Epo) induces a dose-dependent increase in intracellular free Ca2+ ([Ca2+]i ) in human erythroblasts, which is dependent on extracellular Ca2+ and blocked by high doses of nifedipine or Ni2+. In addition, pretreatment of human erythroblasts with mouse antihuman erythropoietin receptor antibody but not mouse immunopure IgG blocked the Epo-induced [Ca2+]i increase, indicating the specificity of the Ca2+ response to Epo stimulation. In this study, the erythropoietin-regulated calcium channel was identified by single channel recordings. Use of conventional whole cell patch-clamp failed to detect Epo-induced whole cell Ca2+ current. To minimize washout of cytosolic constituents, we next used nystatin perforated patch, but did not find any Epo-induced whole cell Ca2+ current. Using Ba2+ (30 mmol/L) as charge carrier in cell-attached patches, we detected single channels with unitary conductance of 3.2 pS, reversal potential of +72 mV, and whose unitary current (at +10 mV) increased monotonically with increasing Ba2+ concentrations. Channel open probability did not appreciably change over the voltage range (−50 to +30 mV) tested. Epo (2 U/mL) increased both mean open time (from 4.27 ± 0.75 to 11.15 ± 1.80 ms) and open probability (from 0.26 ± 0.06 to 2.56 ± 0.59%) of this Ba2+-permeable channel. Our data strongly support the conclusion that the Epo-induced [Ca2+]i increase in human erythroblasts is mediated via Ca2+ entry through a voltage-independent Ca2+ channel.

scholarly journals Modulation of Calcium Channels in Human Erythroblasts by Erythropoietin

Blood ◽  
1997 ◽  
Vol 89 (1) ◽  
pp. 92-100 ◽  
Author(s):  
Joseph Y. Cheung ◽  
Xue-Qian Zhang ◽  
Krister Bokvist ◽  
Douglas L. Tillotson ◽  
Barbara A. Miller
Keyword(s):  
Single Channel ◽  
Reversal Potential ◽  
Erythropoietin Receptor ◽  
Single Channels ◽  
Open Probability ◽  
Whole Cell ◽  
Voltage Range ◽  
Whole Cell Patch Clamp ◽  
Open Time ◽  
High Doses

Erythropoietin (Epo) induces a dose-dependent increase in intracellular free Ca2+ ([Ca2+]i ) in human erythroblasts, which is dependent on extracellular Ca2+ and blocked by high doses of nifedipine or Ni2+. In addition, pretreatment of human erythroblasts with mouse antihuman erythropoietin receptor antibody but not mouse immunopure IgG blocked the Epo-induced [Ca2+]i increase, indicating the specificity of the Ca2+ response to Epo stimulation. In this study, the erythropoietin-regulated calcium channel was identified by single channel recordings. Use of conventional whole cell patch-clamp failed to detect Epo-induced whole cell Ca2+ current. To minimize washout of cytosolic constituents, we next used nystatin perforated patch, but did not find any Epo-induced whole cell Ca2+ current. Using Ba2+ (30 mmol/L) as charge carrier in cell-attached patches, we detected single channels with unitary conductance of 3.2 pS, reversal potential of +72 mV, and whose unitary current (at +10 mV) increased monotonically with increasing Ba2+ concentrations. Channel open probability did not appreciably change over the voltage range (−50 to +30 mV) tested. Epo (2 U/mL) increased both mean open time (from 4.27 ± 0.75 to 11.15 ± 1.80 ms) and open probability (from 0.26 ± 0.06 to 2.56 ± 0.59%) of this Ba2+-permeable channel. Our data strongly support the conclusion that the Epo-induced [Ca2+]i increase in human erythroblasts is mediated via Ca2+ entry through a voltage-independent Ca2+ channel.

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