Tmem16a‐induced Cl
            Ca
            currents are regulated via phosphotransferase activity

1. Intracellular recording in the in vitro slice preparation and whole-cell, patch-clamp recording of acutely dissociated neurons from the rat lateral geniculate nucleus (LGN) were combined to study the Ca currents underlying their electrical responses. In slices from young animals (postnatal days 13-16), we found that dorsal LGN neurons have responses similar to those of adult preparations, including the presence of a low-threshold Ca spike (LTS). After enzymatic isolation of LGN neurons from the same animals, the firing properties appeared well preserved, as indicated by whole-cell, current-clamp recordings from dissociated multipolar cells (presumably geniculocortical relay neurons). 2. Two types of Ca currents were identified in voltage-clamped, isolated LGN neurons on the basis of their voltage dependency, pharmacology, and selectivity properties. These two currents resemble the low-voltage-activated (LVA) and high-voltage-activated (HVA) Ca channels found in rat sensory neurons (9). 3. The LVA current component required negative potentials (less than -80 mV) to deinactivate completely, started to activate around -60 mV and reached a plateau level around -25 mV. It peaked within 30-6 ms and decayed with a single time constant of approximately 24 ms at -20 mV. Its inactivation curve ranged from -100 to -40 mV, with a half-inactivation near -60 mV. The HVA current component could be isolated by holding the membrane potential positive to -60 mV, activated at potentials positive to -30 mV and peaked around +5 mV. The time-to-peak ranged from 30 to 6 ms in the voltage range from -30 to +35 mV and decayed very slowly with sustained depolarizing pulses (time constant ranged between 1,600 and 40 ms over the same voltage range). 4. The inactivation of LVA Ca current during depolarizing voltage steps was consistent with a voltage-dependent process. The recovery from inactivation after short (100 ms), inactivating prepulses displayed two exponential phases. The slower phase was predominant under conditions that induce large current flow through the membrane, suggesting a Ca-mediated mechanism. 5. The LVA current was preferentially blocked by 50 microM Ni2+, leaving the HVA currents almost unaltered. Fifty micromolars Cd2+, in contrast, seemed more effective in blocking the HVA component of the Ca current.(ABSTRACT TRUNCATED AT 400 WORDS)

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Intracellular Ca2+Dynamics During Spontaneous and Evoked Activity of Leech Heart Interneurons: Low-Threshold Ca Currents and Graded Synaptic Transmission

Journal of Neuroscience ◽

10.1523/jneurosci.20-13-04930.2000 ◽

2000 ◽

Vol 20 (13) ◽

pp. 4930-4943 ◽

Cited By ~ 38

Author(s):

Andrei I. Ivanov ◽

Ronald L. Calabrese

Keyword(s):

Synaptic Transmission ◽

Low Threshold ◽

Evoked Activity ◽

Ca Currents

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Effects of Ca2+ antagonists and antiepileptics on TTX-sensitive Ca currents in isolated rat hippocampal neurons.

The Japanese Journal of Pharmacology ◽

10.1016/s0021-5198(19)39230-3 ◽

1991 ◽

Vol 55 ◽

pp. 281

Author(s):

Kazuyoshi Takahashi ◽

Hiroyuki Kameda ◽

Mikiko Kataoka ◽

Norio Akaike

Keyword(s):

Hippocampal Neurons ◽

Ca Currents ◽

Isolated Rat

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Differential Sensitivity to Intracellular pH Among High- and Low-Threshold Ca2+ Currents in Isolated Rat CA1 Neurons

Journal of Neurophysiology ◽

10.1152/jn.1997.77.2.639 ◽

1997 ◽

Vol 77 (2) ◽

pp. 639-653 ◽

Cited By ~ 79

Author(s):

Geoffrey C. Tombaugh ◽

George G. Somjen

Keyword(s):

Intracellular Ph ◽

Differential Sensitivity ◽

Tetraacetic Acid ◽

Ca1 Neurons ◽

Hippocampal Ca1 Neurons ◽

Hippocampal Ca1 ◽

Internal Ph ◽

Low Threshold ◽

Ca Currents ◽

Isolated Rat

Tombaugh, Geoffrey C. and George G. Somjen. Differential sensitivity to intracellular pH among high- and low-threshold Ca2+ currents in isolated rat CA1 neurons. J. Neurophysiol. 77: 639–653, 1997. The effects of intracellular pH (pHi) on high-threshold (HVA) and low-threshold (LVA) calcium currents were examined in acutely dissociated rat hippocampal CA1 neurons with the use of the whole cell patch-clamp technique (21–23°C). Internal pH was manipulated by external exposure to the weak base NH4Cl or in some cases to the weak acid Na-acetate (20 mM) at constant extracellular pH (7.4). Confocal fluorescence measurements using the pH-sensitive dye SNARF-1 in both dialyzed and intact cells confirmed that NH4Cl caused a reversible alkaline shift. However, the external TEA-Cl concentration used during I Ca recording was sufficient to abolish cellular acidification upon NH4Cl wash out. With 10 mM N-2-hydroxyethylpiperazine- N′-2-ethanesulfonic acid (HEPES) in the pipette, NH4Cl exposure reversibly enhanced HVA currents by 29%, whereas exposure to Na-acetate markedly and reversibly depressed HVA Ca currents by 62%. The degree to which NH4Cl enhanced HVA currents was inversely related to the internal HEPES concentration but was unaffected when internal ethylene glycol-bis(β-aminoethyl ether)- N,N,N′,N′-tetraacetic acid (EGTA) was replaced by equimolar bis-( o-aminophenoxy)- N,N,N′,N′-tetraacetic acid (BAPTA). When depolarizing test pulses were applied shortly after break-in ( V h = −100 mV), NH4Cl caused a proportionally greater increase in the sustained current relative to the peak. The dihydropyridine Ca channel antagonist nifedipine (5 μM) blocked nearly all of this sustained current. A slowly inactivating nifedipine-sensitive (L-type) HVA current could be evoked from a depolarized holding potential of −50 mV; NH4Cl enhanced this current by 40 ± 3% (mean ± SE) and reversibly shifted the tail-current activation curve by +6–8 mV. L-type currents exhibited more rapid rundown than N-type currents; HVA currents remaining after prolonged cell dialysis, or in the presence of nifedipine, inactivated rapidly and were depressed by ω-conotoxin (GVIA). NH4Cl enhanced these N-type currents by 76 ± 9%. LVA Ca currents were observed in 32% of the cells and exhibited little if any rundown. These amiloride-sensitive currents activated at voltages negative to −50 mV, were enhanced by extracellular alkalosis and depressed by extracellular acidosis, but were unaffected by exposure to either NH4Cl or NaAC. These results demonstrate that HVA Ca currents in hippocampal CA1 neurons are bidirectionally modulated by internal pH shifts, and that N-type currents are more sensitive to alkaline shifts than are L- or T-type (N > L > T). Our findings strengthen the idea that distinct cellular processes governed by different Ca channels may be subject to selective modulation by uniform shifts in cytosolic pH.

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Voltage-clamp analysis of the ionic conductances in a leech neuron with a purely calcium-dependent action potential

Journal of Neurophysiology ◽

10.1152/jn.1987.58.6.1468 ◽

1987 ◽

Vol 58 (6) ◽

pp. 1468-1484 ◽

Cited By ~ 13

Author(s):

J. Johansen ◽

J. Yang ◽

A. L. Kleinhaus

Keyword(s):

Steady State ◽

Action Potential ◽

Time Course ◽

Outward Current ◽

Time Constants ◽

Exponential Time ◽

Calcium Dependent ◽

Voltage Dependent ◽

Ca Currents ◽

Single Exponential

1. The purely calcium-dependent action potential of the anterior lateral giant (ALG) cell in the leech Haementeria was examined under voltage clamp. 2. Analysis with ion substitutions showed that the ALG cell action potential is generated by only two time- and voltage-dependent conductance systems, an inward Ca-dependent current (ICa) and an outward Ca-dependent K current IK(Ca). 3. The kinetic properties of the inward current were examined both in Cs-loaded neurons with Ca as the current carrier as well as in Ba-containing Ringer solutions with Ba as the current carrier, since Ba effectively blocked all time- and voltage-dependent outward current. 4. During a maintained depolarization, Ba and Ca currents activated with a time constant tau m, they then inactivated with the decay following a single exponential time course with a time constant tau h. The time constants for decay of both Ba and Ca currents were comparable, suggesting that the mechanism of inactivation of ICa in the ALG cell is largely voltage dependent. In the range of potentials from 5 to 45 mV, tau m varied from 8 to 2 ms and tau h varied from 250 to 125 ms. 5. The activation of currents carried by Ba, after correction for inactivation, could be described reasonably well by the expression I'Ba = I'Ba(infinity) [1--exp(-t/tau m)]. 6. The steady-state activation of the Ba-conductance mBa(infinity) increased sigmoidally with voltage and was approximated by the equation mBa(infinity) = (1 + exp[(Vh-6)/3])-1. The steady-state inactivation hBa(infinity) varied with holding potential and could be described by the equation hBa(infinity) = [1 + exp(Vh + 10/7)]-1. Recovery from inactivation of IBa was best described by the sum of two exponential time courses with time constants of 300 ms and 1.75 s, respectively. 7. The outward current IK(Ca) developed very slowly (0.5–1 s to half-maximal amplitude) and did not inactivate during a 20-s depolarizing command pulse. Tail current decay of IK(Ca) followed a single exponential time course with voltage-dependent time constants of between 360 and 960 ms. The steady-state activation n infinity of IK(Ca) increased sigmoidally with depolarization as described by the equation n infinity = [1 + exp(Vh-13.5)/-8)]-1. 8. The reversal potentials of IK(Ca) tail currents were close to the expected equilibrium potential for potassium and they varied linearly with log [K]o with a slope of 51 mV. These results suggest a high selectivity of the conductance for K ions.(ABSTRACT TRUNCATED AT 400 WORDS)

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