The block of the expressed L‐type calcium channel is modulated by the β3 subunit

Lacinová, Ľubica; Ludwig, A.; Bosse, Eva; Flockerzi, Veit; Hofmann, Franz

doi:10.1016/0014-5793(95)01013-5

Cited by 31 publications

(19 citation statements)

References 24 publications

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“…13,14 Also, the peak ICa,L density is known to be increased by co-expression of the (Cacnb) auxiliary subunit, [14][15][16] although there have been contro- versial results reported for 3 (Cacnb3). 17 On the basis of these reports, the present electrophysiological observations would be explained simply by the decreased amount of the main subunit 1C (Cacna1c) (Cav1.2) in the atrium being compensated for by the increased auxiliary subunit 2 (Cacna2d), leading to similar ICa,L density in the atrium and the ventricle. In this consideration, the voltage dependence of inactivation and activation of ICa,L should show a hyperpolarized shift in the atrium through the increased 2 (Cacna2d), contradictory to our observation of a depolarized shift.…”

Section: Discussionmentioning

confidence: 54%

Molecular and Electrophysiological Differences in the L-Type Ca2+ Channel of the Atrium and Ventricle of Rat Hearts

Hatano

Yamashita

Sekiguchi

et al. 2006

Circ J

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he L-type Ca 2+ channel expressed in cardiac muscle plays an important role in determining the intracellular Ca 2+ and thus the action potential duration of cardiomyocytes. 1 Although Ca 2+ overload is a major cause of myocardial cell injury, 2 blocking this channel could be either beneficial or detrimental. In fact, the available L-type Ca 2+ channel blockers should be useful for treating several types of cardiac arrhythmias, but might cause negative inotropic effects that lead to pump failure. A T-type Ca 2+ channel blocker, mibefradil, has shown potential for preventing tachycardia-induced atrial fibrillation remodeling, 3 although its underlying mechanism of prevention remains unclear. Because the T-type Ca 2+ channel blockers are one of the "atrium specific Ca 2+ channel blockers", regional differences in the L-type Ca 2+ channel blocker, if any, would open a new paradigm for controlling regional intracellular Ca 2+ .The function of the L-type Ca 2+ channel is characterized by its main subunit, 1C (Cacna1c) (Cav1.2), and also the auxiliary subunits 2 (Cacna2d) and (Cacnb). However, there are few reports investigating regional differences in Ca 2+ channel composition. Because previous studies have focused on regional or developmental differences of a single subunit, 4,5 it would be inappropriate to discuss regional differences of the L-type Ca 2+ channel with special reference to the relative expression of the composite subunits. In the present study, to determine whether the composition of the L-type Ca 2+ channel is identical throughout the heart, we analyzed both the distribution of the mRNAs and proteins that comprise the L-type Ca 2+ channel and its electrophysiological properties in rat atria and ventricles. Methods mRNA Analysis and Ribonuclease Protection AssayHearts were harvested from 10-week-old female SpragueDawley (SD) rats. For mRNA analysis, the excised hearts were divided into the sinus-node, the right atrium, the left atrium, the intraventricular septum, the epicardial side of the left ventricular free wall, the endocardial side, the left Methods and ResultsTo determine whether the L-type Ca 2+ channel is identical throughout the heart, the distribution of the mRNAs and proteins comprising the L-type Ca 2+ channel and its electrophysiological properties were analyzed in rat atria and ventricles. The mRNA of 2 -2 (Cacna2d2) was more abundantly expressed in the atrium (~5-fold) than in the ventricle. In contrast, 1C (Cacna1c) (Cav1.2) mRNA was significantly less abundant in the atrium. The level of the 1C (Cacna1c) (Cav1.2) protein was decreased (~0.5-fold) and that of 2 -1 (Cacna2d1) was increased (~2-fold) in the atrium compared with the ventricle. Although the peak ICa,L density showed no significant differences, voltage dependence of inactivation and activation of the current showed a more depolarized shift in the atrium than in the ventricle. Conclusion These results indicate that in the rat heart the L-type Ca 2+ channel differs between the atrium and ventricle with regard to gene expre...

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Section: Discussionmentioning

confidence: 54%

Molecular and Electrophysiological Differences in the L-Type Ca2+ Channel of the Atrium and Ventricle of Rat Hearts

Hatano

Yamashita

Sekiguchi

et al. 2006

Circ J

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“…Faster inactivating Ca 2ϩ currents were found to be more efficiently blocked by PAA than more slowly inactivating Ba 2ϩ currents in cardiomyocytes (2). Heterologously expressed Ltype Ca 2ϩ channels are blocked to a larger extent by PAA when ␤ 3 -subunits, which accelerate current inactivation, are coexpressed with ␣ 1C (29).…”

Section: Resultsmentioning

confidence: 99%

Molecular mechanism of use-dependent calcium channel block by phenylalkylamines: Role of inactivation

Hering

Aczél

Kraus

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

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The role of channel inactivation in the molecular mechanism of calcium (Ca channel block by PAA is, however, still not understood. High affinity determinants of the PAA-receptor site of L-type Ca 2ϩ channels have recently been identified on transmembrane segment IVS6 by mutating putative pore-orientated amino acids and subsequent screening of the resulting mutants for PAA-sensitivity (8) or by transferring the responsible L-type amino acids into the ␣ 1A subunit of P͞Q-type channels thereby introducing PAA sensitivity (10, 11). The resulting highly PAA sensitive triple ␣ 1A mutant AL25 (11) displayed significantly faster inactivation kinetics than the wild-type channel. Furthermore, an even more rapid inactivation and higher apparent PAA sensitivity was induced into ␣ 1A if an additional phenylalanine in position 1,805 of AL25 was mutated to the corresponding L-type methionine in IVS6 suggesting a close link between inactivation properties of the channel and use-dependent block by PAA.However, because mutations of the PAA-receptor site itself or of closely located amino acids may not only affect channel inactivation but also the interaction of PAAs with their binding site on transmembrane segment IVS6, no unequivocal conclusions about the role of inactivation in channel block could be drawn (11). To answer this question we designed Ca 2ϩ channels that inactivate at different rates by site directed mutagenesis of segment IIIS6.We report here that substitutions of putative pore-lining amino acids that are highly conserved between ␣ 1A , ␣ 1S , and ␣ 1C gradually reduce the rate of channel inactivation while also gradually reducing use-dependent block by (Ϫ)D600. Our data indicate that changes in Ca 2ϩ channel inactivation induced by site directed mutagenesis modulate use-dependent Ca 2ϩ channel block by PAA. This suggests that channel inactivation is an important determinant of use-dependent Ca 2ϩ channel block by these drugs.

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“…First evidence for ␤-subunit-dependent PAA sensitivity was reported by Lacinova et al, 25 who observed a higher sensitivity of Ca v 1.2 for (-)gallopamil and verapamil when the ␣ 1 1.2-subunit was coexpressed together with the ␤ 3 -subunit compared with cells transfected solely with ␣ 1 1.2. We have later demonstrated that the PAA sensitivity of a mutant ␣ 1 2.1 construct is determined by ␤-subunitdependent inactivation properties (␣ 1A-PAA ).…”

Section: ␤-Subunit Composition Of Ca V 12 Affects Voltage-dependent mentioning

confidence: 89%

On the Role of Ca ²⁺ - and Voltage-Dependent Inactivation in Ca _v 1.2 Sensitivity for the Phenylalkylamine (-)Gallopamil

Sokolov¹,

Timin²,

Hering³

2001

Circulation Research

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Abstract-L-type calcium channels (Ca v 1.m) inactivate in response to elevation of intracellular Ca 2ϩ (Ca 2ϩ -dependent inactivation) and additionally by conformational changes induced by membrane depolarization (fast and slow voltage-dependent inactivation). Molecular determinants of inactivation play an essential role in channel inhibition by phenylalkylamines (PAAs). The relative impacts, however, of Ca 2ϩ -dependent and voltage-dependent inactivation in Ca v 1.2 sensitivity for PAAs remain unknown. In order to analyze the role of the different inactivation processes, we expressed Ca v 1.2 constructs composed of different ␤-subunits (␤ 1a -, ␤ 2a -, or ␤ 3 -subunit) in Xenopus oocytes and estimated their (-)gallopamil sensitivity by means of the two-microelectrode voltage clamp with either Ba 2ϩ or Ca 2ϩ as charge carrier. Ca v 1.2 consisting of the ␤ 2a -subunit displayed the slowest inactivation and the lowest apparent sensitivity for the PAA (-)gallopamil. A significantly higher apparent (-)gallopamil-sensitivity with Ca 2ϩ as charge carrier was observed for all 3 ␤-subunit compositions. The kinetics of Ca 2ϩ -dependent inactivation and slow voltage-dependent inactivation were not affected by drug. The higher sensitivity of the Ca v 1.2 channels for (-)gallopamil with Ca 2ϩ as charge carrier results from slower recovery ( rec,Ca Ϸ15 seconds versus rec,Ba Ϸ3 to 5 seconds) from a PAA-induced channel conformation. We propose a model where (-) antagonists, ie, phenylalkylamines (PAAs), benzothiazepines (ie, diltiazem) and 1,4-dihydropyridines (DHPs). [2][3][4][5] About 20 years ago, several groups demonstrated that Ca v 1.m inhibition by PAAs and diltiazem occurs predominately during membrane depolarizations ("use-dependent" action) when the channels are primarily in the open or inactivated conformation. [2][3][4]6 Since then, numerous studies in myocardial and smooth muscle cells have shown that Ca 2ϩ channel inhibition by these compounds, as well as by the new compound mibefradil, reflect a balance between channel shut-off during membrane depolarization and subsequent recovery at rest. [7][8][9][10][11] Over the last three years there has been substantial progress toward understanding the role of inactivation in Ca 2ϩ channel inhibition by Ca 2ϩ antagonists. Site directed mutagenesis enabled a detailed analysis of the impact of this process in PAA sensitivity. A comparison of the PAA sensitivities of Ca v 2.1 mutants and chimeric channel constructs inactivating at different rates revealed a strong correlation between the rates of fast voltage-dependent inactivation and apparent PAA sensitivities. 11-13 Similar findings were reported for Ca 2ϩ channel block by diltiazem. 11,14 Subsequently, the studies concentrated on the localization of inactivation determinants that are relevant for channel inhibition. Thus, inactivation determinants in the loop between domains I and II and ␤-subunit interaction have been shown to control PAA sensitivity of a Ca v 2.1 mutant 13 as well as the mibefradilsensitivity of wild ...

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The block of the expressed L‐type calcium channel is modulated by the β₃ subunit

Cited by 31 publications

References 24 publications

Molecular and Electrophysiological Differences in the L-Type Ca<sup>2+</sup> Channel of the Atrium and Ventricle of Rat Hearts

Molecular and Electrophysiological Differences in the L-Type Ca<sup>2+</sup> Channel of the Atrium and Ventricle of Rat Hearts

Molecular mechanism of use-dependent calcium channel block by phenylalkylamines: Role of inactivation

On the Role of Ca ²⁺ - and Voltage-Dependent Inactivation in Ca _v 1.2 Sensitivity for the Phenylalkylamine (-)Gallopamil

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The block of the expressed L‐type calcium channel is modulated by the β3 subunit

Cited by 31 publications

References 24 publications

Molecular and Electrophysiological Differences in the L-Type Ca<sup>2+</sup> Channel of the Atrium and Ventricle of Rat Hearts

Molecular and Electrophysiological Differences in the L-Type Ca<sup>2+</sup> Channel of the Atrium and Ventricle of Rat Hearts

Molecular mechanism of use-dependent calcium channel block by phenylalkylamines: Role of inactivation

On the Role of Ca 2+ - and Voltage-Dependent Inactivation in Ca v 1.2 Sensitivity for the Phenylalkylamine (-)Gallopamil

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The block of the expressed L‐type calcium channel is modulated by the β₃ subunit

On the Role of Ca ²⁺ - and Voltage-Dependent Inactivation in Ca _v 1.2 Sensitivity for the Phenylalkylamine (-)Gallopamil