A Complex of RIM2alpha and RIM-Binding Protein 2 Stabilizes Slow Voltage-Dependent Inactivation of Cochlear Inner Hair Cell Cav1.3 L-Type Ca2+ Channels

The whole cell version of the patch-clamp technique was used to characterize voltage-gated Ca2+ channels in the calcitonin-secreting rat thyroid C-cell line 6-23 (clone 6). Three types of Ca2+ channels could be distinguished based on differences in voltage dependence, kinetics, and pharmacological sensitivity. T-type current was half-maximal at -31 mV, showed steady-state voltage-dependent inactivation that was half-maximal at -57 mV, inactivated with a voltage-dependent time constant that reached a minimum of 20 ms at potentials positive to -20 mV, and deactivated with a single time constant of approximately 2 ms at -80 mV. Reactivation of inactivated channels occurred with a time constant of 1.26 s at -90 mV. T current was selectively blocked by Ni2+ at concentrations between 5 and 50 microM. La3+ and Y3+ blocked the T current at 10- to 20-fold lower concentrations. Dihydropyridine-sensitive L-type current was half-maximal at a test potential of -3 mV and was approximately doubled in size when Ba2+ replaced Ca2+ as the charge carrier. Unlike L-type Ca2+ current in many cells, this current in C-cells displayed little Ca(2+)-dependent inactivation. N-type current was composed of inactivating and sustained components that were inhibited by omega-conotoxin. The inactivating component was half-maximal at +9 mV and could be fitted by two exponentials with time constants of 22 and 142 ms. A slow inactivation of N current with a time constant of 24.9 s was observed upon switching the holding potential from -80 to -40 mV. These results demonstrate that, similar to other neural crest derived cells, thyroid C-cells express multiple Ca2+ channels, including one previously observed only in neurons.

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Ion-dependent Inactivation of Barium Current through L-type Calcium Channels

The Journal of General Physiology ◽

10.1085/jgp.109.4.449 ◽

1997 ◽

Vol 109 (4) ◽

pp. 449-461 ◽

Cited By ~ 86

Author(s):

Gonzalo Ferreira ◽

Jianxun Yi ◽

Eduardo Ríos ◽

Roman Shirokov

Keyword(s):

Ionic Current ◽

Reversal Potential ◽

Slow Phase ◽

Gating Currents ◽

Current Decay ◽

Gating Charge ◽

Long Duration ◽

Dependent Inactivation ◽

Voltage Dependent ◽

Ca2 Channels

It is widely believed that Ba2+ currents carried through L-type Ca2+ channels inactivate by a voltage- dependent mechanism similar to that described for other voltage-dependent channels. Studying ionic and gating currents of rabbit cardiac Ca2+ channels expressed in different subunit combinations in tsA201 cells, we found a phase of Ba2+ current decay with characteristics of ion-dependent inactivation. Upon a long duration (20 s) depolarizing pulse, IBa decayed as the sum of two exponentials. The slow phase (τ ≈ 6 s, 21°C) was parallel to a reduction of gating charge mobile at positive voltages, which was determined in the same cells. The fast phase of current decay (τ ≈ 600 ms), involving about 50% of total decay, was not accompanied by decrease of gating currents. Its amplitude depended on voltage with a characteristic U-shape, reflecting reduction of inactivation at positive voltages. When Na+ was used as the charge carrier, decay of ionic current followed a single exponential, of rate similar to that of the slow decay of Ba2+ current. The reduction of Ba2+ current during a depolarizing pulse was not due to changes in the concentration gradients driving ion movement, because Ba2+ entry during the pulse did not change the reversal potential for Ba2+. A simple model of Ca2+-dependent inactivation (Shirokov, R., R. Levis, N. Shirokova, and E. Ríos. 1993. J. Gen. Physiol. 102:1005–1030) robustly accounts for fast Ba2+ current decay assuming the affinity of the inactivation site on the α1 subunit to be 100 times lower for Ba2+ than Ca2+.

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Isolation of Voltage Dependent Calcium Current in Chick Inner Hair Cell

Korean Journal of Otorhinolaryngology - Head and Neck Surgery ◽

10.3342/kjorl-hns.2009.52.8.655 ◽

2009 ◽

Vol 52 (8) ◽

pp. 655

Author(s):

Seung Hwan Lee ◽

Myung Chul Shin ◽

Tae Hwan Ahn ◽

Ki Yong Kim ◽

Kuk Kim ◽

...

Keyword(s):

Hair Cell ◽

Calcium Current ◽

Inner Hair Cell ◽

Voltage Dependent

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

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1997.272.2.h606 ◽

1997 ◽

Vol 272 (2) ◽

pp. H606-H612 ◽

Cited By ~ 10

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.

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RIM-Binding Protein 2 Promotes a Large Number of CaV1.3 Ca2+-Channels and Contributes to Fast Synaptic Vesicle Replenishment at Hair Cell Active Zones

Frontiers in Cellular Neuroscience ◽

10.3389/fncel.2017.00334 ◽

2017 ◽

Vol 11 ◽

Cited By ~ 18

Author(s):

Stefanie Krinner ◽

Tanvi Butola ◽

SangYong Jung ◽

Carolin Wichmann ◽

Tobias Moser

Keyword(s):

Hair Cell ◽

Synaptic Vesicle ◽

Binding Protein ◽

Active Zones ◽

Ca2 Channels

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Splicing of an automodulatory domain in Cav1.4 Ca2+ channels confers distinct regulation by calmodulin

The Journal of General Physiology ◽

10.1085/jgp.201812140 ◽

2018 ◽

Vol 150 (12) ◽

pp. 1676-1687 ◽

Cited By ~ 2

Author(s):

Brittany Williams ◽

Françoise Haeseleer ◽

Amy Lee

Keyword(s):

Night Blindness ◽

Feedback Regulation ◽

Negative Feedback Regulation ◽

Visual Signaling ◽

Naturally Occurring ◽

Dependent Inactivation ◽

Voltage Dependent ◽

Normal Physiological Function ◽

Ca2 Channels

Ca2+ influx through Cav1.4 L-type Ca2+ channels supports the sustained release of glutamate from photoreceptor synaptic terminals in darkness, a process that is critical for vision. Consistent with this role, Cav1.4 exhibits weak Ca2+-dependent inactivation (CDI)—a negative feedback regulation mediated by Ca2+-bound calmodulin (CaM). CaM binds to a conserved IQ domain in the proximal C-terminal domain of Cav channels, but in Cav1.4, a C-terminal modulatory domain (CTM) disrupts interactions with CaM. Exon 47 encodes a portion of the CTM and is deleted in a Cav1.4 splice variant (Cav1.4Δex47) that is highly expressed in the human retina. Cav1.4Δex47 exhibits CDI and enhanced voltage-dependent activation, similar to that caused by a mutation that is associated with congenital stationary night blindness type 2, in which the CTM is deleted (K1591X). The presence of CDI and very negative activation thresholds in a naturally occurring variant of Cav1.4 are perplexing considering that these properties are expected to be maladaptive for visual signaling and result in night blindness in the case of K1591X. Here we show that Cav1.4Δex47 and K1591X exhibit fundamental differences in their regulation by CaM. In Cav1.4Δex47, CDI requires both the N-terminal (N lobe) and C-terminal (C lobe) lobes of CaM to bind Ca2+, whereas CDI in K1591X is driven mainly by Ca2+ binding to the C lobe. Moreover, the CaM N lobe causes a Ca2+-dependent enhancement of activation of Cav1.4Δex47 but not K1591X. We conclude that the residual CTM in Cav1.4Δex47 enables a form of CaM N lobe regulation of activation and CDI that is absent in K1591X. Interaction with the N lobe of CaM, which is more sensitive to global elevations in cytosolic Ca2+ than the C lobe, may allow Cav1.4Δex47 to be modulated by a wider range of synaptic Ca2+ concentrations than K1591X; this may distinguish the normal physiological function of Cav1.4Δex47 from the pathological consequences of K1591X.

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Voltage dependent Ca2+-channels are inhibited during the activation of PTX-sensitive GTP-binding protein

Neuroscience Research Supplements ◽

10.1016/0921-8696(91)90697-l ◽

1991 ◽

Vol 16 ◽

pp. 20

Author(s):

Hirobumi Higuchi ◽

Osamu Chiba ◽

Kazuhiko Sasaki ◽

Makoto Sato

Keyword(s):

Binding Protein ◽

Gtp Binding Protein ◽

Gtp Binding ◽

Voltage Dependent ◽

Ca2 Channels

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A Ca2+-induced Ca2+ Release Mechanism Involved in Asynchronous Exocytosis at Frog Motor Nerve Terminals

The Journal of General Physiology ◽

10.1085/jgp.112.5.593 ◽

1998 ◽

Vol 112 (5) ◽

pp. 593-609 ◽

Cited By ~ 63

Author(s):

K. Narita ◽

T. Akita ◽

M. Osanai ◽

T. Shirasaki ◽

H. Kijima ◽

...

Keyword(s):

Motor Nerve ◽

Ryanodine Receptors ◽

Pause Duration ◽

Release Mechanism ◽

Nerve Terminals ◽

Presynaptic Terminals ◽

Motor Nerve Terminals ◽

Dependent Inactivation ◽

Voltage Dependent ◽

Ca2 Channels

The extent to which Ca2+-induced Ca2+ release (CICR) affects transmitter release is unknown. Continuous nerve stimulation (20–50 Hz) caused slow transient increases in miniature end-plate potential (MEPP) frequency (MEPP-hump) and intracellular free Ca2+ ([Ca2+]i) in presynaptic terminals (Ca2+-hump) in frog skeletal muscles over a period of minutes in a low Ca2+, high Mg2+ solution. Mn2+ quenched Indo-1 and Fura-2 fluorescence, thus indicating that stimulation was accompanied by opening of voltage-dependent Ca2+ channels. MEPP-hump depended on extracellular Ca2+ (0.05–0.2 mM) and stimulation frequency. Both the Ca2+- and MEPP-humps were blocked by 8-(N,N-diethylamino)octyl3,4,5-trimethoxybenzoate hydrochloride (TMB-8), ryanodine, and thapsigargin, but enhanced by CN−. Thus, Ca2+-hump is generated by the activation of CICR via ryanodine receptors by Ca2+ entry, producing MEPP-hump. A short interruption of tetanus (<1 min) during MEPP-hump quickly reduced MEPP frequency to a level attained under the effect of TMB-8 or thapsigargin, while resuming tetanus swiftly raised MEPP frequency to the previous or higher level. Thus, the steady/equilibrium condition balancing CICR and Ca2+ clearance occurs in nerve terminals with slow changes toward a greater activation of CICR (priming) during the rising phase of MEPP-hump and toward a smaller activation during the decay phase. A short pause applied after the end of MEPP- or Ca2+-hump affected little MEPP frequency or [Ca2+]i, but caused a quick increase (faster than MEPP- or Ca2+-hump) after the pause, whose magnitude increased with an increase in pause duration (<1 min), suggesting that Ca2+ entry-dependent inactivation, but not depriming process, explains the decay of the humps. The depriming process was seen by giving a much longer pause (>1 min). Thus, ryanodine receptors in frog motor nerve terminals are endowed with Ca2+ entry-dependent slow priming and fast inactivation mechanisms, as well as Ca2+ entry-dependent activation, and involved in asynchronous exocytosis. Physiological significance of CICR in presynaptic terminals was discussed.

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