Properties of inward calcium current in guinea pig ureteral myocytes

1997 ◽  
Vol 272 (2) ◽  
pp. C543-C549 ◽  
Author(s):  
J. L. Sui ◽  
C. Y. Kao
Keyword(s):  
Action Potentials ◽  
Calcium Current ◽  
Inactivation Kinetics ◽  
Slow Inactivation ◽  
Time Constants ◽  
Channel Inactivation ◽  
Steady State Inactivation ◽  
Window Current ◽  
Kinetics Of ◽  
Ca2 Channels

Ureteral myocytes of guinea pigs have L-type Ca2+ channels (I(Ca)). In 3 mM Ca2+, maximum I(Ca) was 3.38 microA/cm2. Voltage at which conductance is 50% of maximum (V0.5) of I(Ca) was -1.0 mV in 3 mM Ca2+ and +22 mV in 30 mM Ca2+, with slope factors of 8 mV. V0.5 of steady-state inactivation of I(Ca) was -16.2 and +1.1 mV in 3 and 30 mM Ca2+, respectively, with similar slope factors of about -6 mV. A window current reaching 20-25% of the maximum I(Ca) was active between -20 and 0 mV. I(Ca) inactivated very slowly, with time constants of 217.6 and 2,455.9 ms with no voltage dependency. When Ba2+ was used as the charge carrier, the amplitude and inactivation kinetics of the Ba2+ current were similar to those for I(Ca). These results indicate that the ureteral myocyte has little Ca2+-mediated Ca2+ channel inactivation, a feature significantly associated with the slow I(Ca) inactivation. The slow inactivation and the window current are essential for the sustained membrane depolarization during the plateau of ureteral action potentials.

scholarly journals Fast and Slow Inactivation Kinetics of the Ca2+Channels ECaC1 and ECaC2 (TRPV5 and TRPV6)

2002 ◽  
Vol 277 (34) ◽  
pp. 30852-30858 ◽  
Author(s):  
Bernd Nilius ◽  
Jean Prenen ◽  
Joost G. J. Hoenderop ◽  
Rudi Vennekens ◽  
Susan Hoefs ◽  
...  
Keyword(s):  
Inactivation Kinetics ◽  
Slow Inactivation ◽  
Kinetics Of ◽  
Ca2 Channels

scholarly journals Dependence of hormone secretion on activation-inactivation kinetics of voltage-sensitive Ca2+ channels in pituitary gonadotrophs.

1990 ◽  
Vol 87 (22) ◽  
pp. 8855-8859 ◽  
Author(s):  
S. S. Stojilkovic ◽  
T. Iida ◽  
M. A. Virmani ◽  
S. Izumi ◽  
E. Rojas ◽  
...  
Keyword(s):  
Hormone Secretion ◽  
Inactivation Kinetics ◽  
Kinetics Of ◽  
Ca2 Channels

Distinct kinetics of cloned T-type Ca2 +  channels lead to differential Ca2 +  entry and frequency-dependence during mock action potentials

1999 ◽  
Vol 11 (12) ◽  
pp. 4149-4158 ◽  
Author(s):  
Andrei S. Kozlov ◽  
Frank McKenna ◽  
Jung-Ha Lee ◽  
Leanne L. Cribbs ◽  
Edward Perez-Reyes ◽  
...  
Keyword(s):  
Frequency Dependence ◽  
Action Potentials ◽  
Kinetics Of ◽  
Ca2 Channels

Subthreshold Inactivation of Na+ and K+Channels Supports Activity-Dependent Enhancement of Back-Propagating Action Potentials in Hippocampal CA1

2001 ◽  
Vol 85 (2) ◽  
pp. 1013-1016 ◽  
Author(s):  
Enhui Pan ◽  
Costa M. Colbert
Keyword(s):  
Time Constant ◽  
Action Potentials ◽  
Pyramidal Neurons ◽  
Synaptic Activity ◽  
Inactivation Kinetics ◽  
Potential Range ◽  
Channel Inactivation ◽  
Type K ◽  
Dendritic Membrane ◽  
Hippocampal Ca1

Back-propagating action potentials in CA1 pyramidal neurons may provide the postsynaptic dendritic depolarization necessary for the induction of long-term synaptic plasticity. The amplitudes of back-propagating action potentials are not all or none but are limited in amplitude by dendritic A-type K+ channels. Previous studies of back-propagating action potentials have suggested that prior depolarization of the dendritic membrane reduces A-type channel availability through inactivation, resulting in an enhanced, or boosted, dendritic action potential. However, inactivation kinetics in the subthreshold potential range have not been directly measured. Furthermore, the corresponding rates of Na+channel inactivation with depolarization have not been considered. Here we report in cell-attached patches (150–220 μm from the soma, 32°C) that at 20-mV positive to rest, A-type K+channels inactivated with a single exponential time constant of 6 ms, whereas Na+ channels inactivated with a time constant of 37 ms. The ratio of available Na+ to K+ current increased as the duration of the depolarization increased. Thus the subthreshold properties of Na+ and A-type K+ channels provide a mechanism by which information about the level of synaptic activity may be encoded in the amplitude of back-propagating action potentials.

Phospholamban deficiency alters inactivation kinetics of L-type Ca2+ channels in mouse ventricular myocytes

1997 ◽  
Vol 272 (2) ◽  
pp. H606-H612 ◽  
Author(s):  
H. Masaki ◽  
Y. Sato ◽  
W. Luo ◽  
E. G. Kranias ◽  
A. Yatani
Keyword(s):  
Ventricular Myocytes ◽  
Mammalian Species ◽  
Cardiac Cells ◽  
Inactivation Kinetics ◽  
Compensatory Mechanism ◽  
Channel Inactivation ◽  
Dependent Inactivation ◽  
Voltage Dependent ◽  
Channel Currents ◽  
Ca2 Channels

Entry of Ca2+ through voltage-dependent L-type Ca2+ channels is critical for contraction in cardiac cells. In recent studies, cells from phospholamban (PLB) knockout (PLB-KO) mouse hearts showed significantly increased basal contractility with enhanced sarcoplasmic reticulum (SR) Ca2+ uptake. To test whether these effects of PLB ablation were associated with alterations of L-type Ca2+ channel function, we compared the properties of Ca2+ channel currents (I(Ca)) in ventricular myocytes isolated from wild-type (WT) and PLB-KO mouse hearts. L-type Ca2+ channels from mouse myocytes exhibited voltage-dependent gating and sensitivity to dihydropyridine drugs, similar to other mammalian species, and these properties were not altered by PLB ablation. I(Ca) from both WT and PLB-KO cells revealed two (fast and slow) components of inactivation kinetics. However, the proportion of the faster component was significantly larger in PLB-KO cells. Ryanodine (10 microM) reduced the rate of inactivation of I(Ca) for both WT and PLB-KO cells, but the reduction was more prominent in PLB-KO cells compared with WT cells. In contrast, the inactivation in a Ba2+ solution could be fitted by a single exponential similar to the slower component in Ca2+, and this was not altered in PLB-KO cells. The increase in the fast Ca2+-dependent inactivation component in PLB-KO cells supports the hypothesis that Ca2+ released from the SR regulates Ca2+ channel inactivation by affecting the levels of Ca2+ near the channel and suggests that this may be an important compensatory mechanism in the hyperdynamic PLB-KO heart.

scholarly journals Kinetics of the course of inactivation of aminoacylase by 1,10-phenanthroline

1992 ◽  
Vol 281 (1) ◽  
pp. 285-290 ◽  
Author(s):  
Z X Wang ◽  
H B Wu ◽  
X C Wang ◽  
H M Zhou ◽  
C L Tsou
Keyword(s):  
Enzyme Activity ◽  
Active Site ◽  
Inactivation Kinetics ◽  
Slow Inactivation ◽  
Phenanthroline Complex ◽  
Rapid Reaction ◽  
Kinetics Of ◽  
Active Site Conformation ◽  
Inhibited Enzyme ◽  
Substrate Competition

The kinetic theory of the substrate reaction during modification of enzyme activity previously described [Tsou (1988) Adv. Enzymol. Relat. Areas Mol. Biol. 61, 381-436] has been applied to a study on the kinetics of the course of inactivation of aminoacylase by 1,10-phenanthroline. Upon dilution of the enzyme that had been incubated with 1,10-phenanthroline into the reaction mixture, the activity of the inhibited enzyme gradually increased, indicating dissociation of a reversible enzyme–1,10-phenanthroline complex. The kinetics of the substrate reaction with different concentrations of the substrate chloroacetyl-L-alanine and the inactivator suggest a complexing mechanism for inactivation by, and substrate competition with, 1,10-phenanthroline at the active site. The inactivation kinetics are single phasic, showing that the initial formation of an enzyme-Zn(2+)-1,10-phenanthroline complex is a relatively rapid reaction, followed by a slow inactivation step that probably involves a conformational change of the enzyme. The presence of Zn2+ apparently stabilizes an active-site conformation required for enzyme activity.

scholarly journals A rapidly activating and slowly inactivating potassium channel cloned from human heart. Functional analysis after stable mammalian cell culture expression.

1993 ◽  
Vol 101 (4) ◽  
pp. 513-543 ◽  
Author(s):  
D J Snyders ◽  
M M Tamkun ◽  
P B Bennett
Keyword(s):  
Cell Lines ◽  
Time Course ◽  
Reversal Potential ◽  
Delayed Rectifier ◽  
Inactivation Kinetics ◽  
Constant Field ◽  
Slow Inactivation ◽  
Time Constants ◽  
K Concentration ◽  
External K

The electrophysiological properties of HK2 (Kv1.5), a K+ channel cloned from human ventricle, were investigated after stable expression in a mouse Ltk- cell line. Cell lines that expressed HK2 mRNA displayed a current with delayed rectifier properties at 23 degrees C, while sham transfected cell lines showed neither specific HK2 mRNA hybridization nor voltage-activated currents under whole cell conditions. The expression of the HK2 current has been stable for over two years. The dependence of the reversal potential of this current on the external K+ concentration (55 mV/decade) confirmed K+ selectivity, and the tail envelope test was satisfied, indicating expression of a single population of K+ channels. The activation time course was fast and sigmoidal (time constants declined from 10 ms to < 2 ms between 0 and +60 mV). The midpoint and slope factor of the activation curve were Eh = -14 +/- 5 mV and k = 5.9 +/- 0.9 (n = 31), respectively. Slow partial inactivation was observed especially at large depolarizations (20 +/- 2% after 250 ms at +60 mV, n = 32), and was incomplete in 5 s (69 +/- 3%, n = 14). This slow inactivation appeared to be a genuine gating process and not due to K+ accumulation, because it was present regardless of the size of the current and was observed even with 140 mM external K+ concentration. Slow inactivation had a biexponential time course with largely voltage-independent time constants of approximately 240 and 2,700 ms between -10 and +60 mV. The voltage dependence of slow inactivation overlapped with that of activation: Eh = -25 +/- 4 mV and k = 3.7 +/- 0.7 (n = 14). The fully activated current-voltage relationship displayed outward rectification in 4 mM external K+ concentration, but was more linear at higher external K+ concentrations, changes that could be explained in part on the basis of constant field (Goldman-Hodgkin-Katz) rectification. Activation and inactivation kinetics displayed a marked temperature dependence, resulting in faster activation and enhanced inactivation at higher temperature. The current was sensitive to low concentrations of 4-aminopyridine, but relatively insensitive to external TEA and to high concentrations of dendrotoxin. The expressed current did not resemble either the rapid or the slow components of delayed rectification described in guinea pig myocytes. However, this channel has many similarities to the rapidly activating delayed rectifying currents described in adult rat atrial and neonatal canine epicardial myocytes.(ABSTRACT TRUNCATED AT 400 WORDS)

A novel SCN5A mutation associated with long QT-3: altered inactivation kinetics and channel dysfunction

2002 ◽  
Vol 10 (3) ◽  
pp. 191-197 ◽  
Author(s):  
Ilaria Rivolta ◽  
Colleen E. Clancy ◽  
Michihiro Tateyama ◽  
Huajun Liu ◽  
Silvia G. Priori ◽  
...  
Keyword(s):  
Inactivation Kinetics ◽  
Long Qt ◽  
Α Subunit ◽  
Inactivation Curve ◽  
Recovery From Inactivation ◽  
Steady State Inactivation ◽  
Window Current ◽  
Rate Of Recovery ◽  
Sustained Inward Current ◽  
Congenital Long Qt Syndrome

Mutations in the gene ( SCN5A) encoding the α-subunit of the cardiac Na+ channel cause congenital long QT syndrome (LQT-3). Here we describe a novel LQT-3 mutation I1768V (I1768V) located in the sixth transmembrane spanning segment of domain IV. This mutation is unusual in that it is located within a transmembrane spanning domain and does not promote the typically observed sustained inward current corresponding to a gain of channel function (bursting). Rather, I1768V increases the rate of recovery from inactivation and increases the channel availability, observed as a positive shift of the steady-state inactivation curve (+7.6 mV). Using a Markovian model of the cardiac Na+ channel, we simulated these changes in gating behavior and demonstrated that a small increase in the rate of recovery from inactivation is sufficient to explain all of the experimentally observed current changes. The effect of these alterations in channel gating results in an increase in window current that may act to disrupt cardiac repolarization.

scholarly journals Endogenous intracellular calcium buffering and the activation/inactivation of HVA calcium currents in rat dentate gyrus granule cells.

1991 ◽  
Vol 98 (5) ◽  
pp. 941-967 ◽  
Author(s):  
G Köhr ◽  
I Mody
Keyword(s):  
Dentate Gyrus ◽  
Granule Cells ◽  
Calcium Currents ◽  
High Threshold ◽  
Single Class ◽  
Adult Rat ◽  
Channel Inactivation ◽  
Calbindin D28k ◽  
Kinetics Of ◽  
Ca2 Channels

Granule cells acutely dissociated from the dentate gyrus of adult rat brains displayed a single class of high-threshold, voltage-activated (HVA) Ca2+ channels. The kinetics of whole-cell Ca2+ currents recorded with pipette solutions containing an intracellular ATP regenerating system but devoid of exogenous Ca2+ buffers, were fit best by Hodgkin-Huxley kinetics (m2h), and were indistinguishable from those recorded with the nystatin perforated patch method. In the absence of exogenous Ca2+ buffers, inactivation of HVA Ca2+ channels was a predominantly Ca(2+)-dependent process. The contribution of endogenous Ca2+ buffers to the kinetics of inactivation was investigated by comparing currents recorded from control cells to currents recorded from neurons that have lost a specific Ca(2+)-binding protein, Calbindin-D28K (CaBP), after kindling-induced epilepsy. Kindled neurons devoid of CaBP showed faster rates of both activation and inactivation. Adding an exogenous Ca2+ chelator, 1,2-bis-(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), to the intracellular solution largely eliminated inactivation in both control and kindled neurons. The results are consistent with the hypothesis that endogenous intraneuronal CaBP contributes significantly to submembrane Ca2+ sequestration at a concentration range and time domain that regulate Ca2+ channel inactivation.

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