Stereoselective modulation of ryanodine-sensitive calcium channels by the δ isomer of hexachlorocyclohexane (δ-HCH)

Isaac N Pessah, Frederick C Mohr, M. Schiedt, R. M. Joy

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

δ-Hexachlorocyclohexane (δ-HCH) is shown to be 30-fold more potent as a positive inotropic with rat atrial strips compared with lindane (γ-HCH). Threshold and ED50 values for enhanced contractile force at a pacing frequency of 0.5 Hz are <1 μM and 2.2 μM for δ-HCH and 40 μM and 63 μM for γ-HCH, respectively. Contracture developed in atria exposed to >4 μM δ-HCH (ED50 = 11 μM) but not in atria exposed to γ-HCH. Uptake and release of Ca++ measured from actively loaded cardiac sarcoplasmic reticulum (SR) vesicles is measured with antipyrylazo III. Although δ-HCH (30 μM) decreases Ca++-dependent ATPase by 20%, it does not significantly alter Ca++ loading in the presence of ruthenium red. Addition of δ-HCH (5- 50 μM) after loading is complete causes rapid, dose-dependent release of Ca++ from SR. Ca++ release induced by δ-HCH is markedly stereoselective. Compared with γ-HCH (50 μM), δ-HCH (50 μM) induces a nearly 20-fold higher initial rate of Ca++ release (4.3 nmol of Ca++/mg/sec). Studies with [3H]ryanodine demonstrate that δ-HCH sharply inhibits Ca++- or daunorubicin-activated radioligand binding (IC50 = 37 and 25 μM, respectively, logit slope = 2). Inhibition of [3H]ryanodine-binding by δ- HCH is stereoselective inasmuch as IC50 values for α, β and γ isomers are >100 μM. The δ-HCH modified Ca++ channel appears to proceed by a noncompetitive mechanism (reducing B(max) in equilibrium experiments) with respect to the conformationally sensitive binding site for [3H]ryanodine. The mechanism is more complex, however, because δ-HCH significantly enhances the observed association rate constant of the remaining sites, and pretreatment of SR induces persistent, concentration-dependent activation or inactivation of [3H]ryanodine-binding sites. The effects of δ-HCH on the ryanodine-sensitive Ca++ channel of cardiac SR is also observed with the brain receptor, suggesting existence of a common mechanism by which chlorinated hydrocarbons can modify Ca++ homeostasis and cell excitability.

Original languageEnglish (US)
Pages (from-to)661-669
Number of pages9
JournalJournal of Pharmacology and Experimental Therapeutics
Volume262
Issue number2
StatePublished - 1992

Fingerprint

Lindane
Ryanodine
Calcium Channels
Sarcoplasmic Reticulum
Inhibitory Concentration 50
Binding Sites
Chlorinated Hydrocarbons
Ruthenium Red
Daunorubicin
Adenosine Triphosphatases
Homeostasis
Brain

ASJC Scopus subject areas

  • Pharmacology

Cite this

@article{dd9614e85f11430d8a691e2eec53f2f7,
title = "Stereoselective modulation of ryanodine-sensitive calcium channels by the δ isomer of hexachlorocyclohexane (δ-HCH)",
abstract = "δ-Hexachlorocyclohexane (δ-HCH) is shown to be 30-fold more potent as a positive inotropic with rat atrial strips compared with lindane (γ-HCH). Threshold and ED50 values for enhanced contractile force at a pacing frequency of 0.5 Hz are <1 μM and 2.2 μM for δ-HCH and 40 μM and 63 μM for γ-HCH, respectively. Contracture developed in atria exposed to >4 μM δ-HCH (ED50 = 11 μM) but not in atria exposed to γ-HCH. Uptake and release of Ca++ measured from actively loaded cardiac sarcoplasmic reticulum (SR) vesicles is measured with antipyrylazo III. Although δ-HCH (30 μM) decreases Ca++-dependent ATPase by 20{\%}, it does not significantly alter Ca++ loading in the presence of ruthenium red. Addition of δ-HCH (5- 50 μM) after loading is complete causes rapid, dose-dependent release of Ca++ from SR. Ca++ release induced by δ-HCH is markedly stereoselective. Compared with γ-HCH (50 μM), δ-HCH (50 μM) induces a nearly 20-fold higher initial rate of Ca++ release (4.3 nmol of Ca++/mg/sec). Studies with [3H]ryanodine demonstrate that δ-HCH sharply inhibits Ca++- or daunorubicin-activated radioligand binding (IC50 = 37 and 25 μM, respectively, logit slope = 2). Inhibition of [3H]ryanodine-binding by δ- HCH is stereoselective inasmuch as IC50 values for α, β and γ isomers are >100 μM. The δ-HCH modified Ca++ channel appears to proceed by a noncompetitive mechanism (reducing B(max) in equilibrium experiments) with respect to the conformationally sensitive binding site for [3H]ryanodine. The mechanism is more complex, however, because δ-HCH significantly enhances the observed association rate constant of the remaining sites, and pretreatment of SR induces persistent, concentration-dependent activation or inactivation of [3H]ryanodine-binding sites. The effects of δ-HCH on the ryanodine-sensitive Ca++ channel of cardiac SR is also observed with the brain receptor, suggesting existence of a common mechanism by which chlorinated hydrocarbons can modify Ca++ homeostasis and cell excitability.",
author = "Pessah, {Isaac N} and Mohr, {Frederick C} and M. Schiedt and Joy, {R. M.}",
year = "1992",
language = "English (US)",
volume = "262",
pages = "661--669",
journal = "Journal of Pharmacology and Experimental Therapeutics",
issn = "0022-3565",
publisher = "American Society for Pharmacology and Experimental Therapeutics",
number = "2",

}

TY - JOUR

T1 - Stereoselective modulation of ryanodine-sensitive calcium channels by the δ isomer of hexachlorocyclohexane (δ-HCH)

AU - Pessah, Isaac N

AU - Mohr, Frederick C

AU - Schiedt, M.

AU - Joy, R. M.

PY - 1992

Y1 - 1992

N2 - δ-Hexachlorocyclohexane (δ-HCH) is shown to be 30-fold more potent as a positive inotropic with rat atrial strips compared with lindane (γ-HCH). Threshold and ED50 values for enhanced contractile force at a pacing frequency of 0.5 Hz are <1 μM and 2.2 μM for δ-HCH and 40 μM and 63 μM for γ-HCH, respectively. Contracture developed in atria exposed to >4 μM δ-HCH (ED50 = 11 μM) but not in atria exposed to γ-HCH. Uptake and release of Ca++ measured from actively loaded cardiac sarcoplasmic reticulum (SR) vesicles is measured with antipyrylazo III. Although δ-HCH (30 μM) decreases Ca++-dependent ATPase by 20%, it does not significantly alter Ca++ loading in the presence of ruthenium red. Addition of δ-HCH (5- 50 μM) after loading is complete causes rapid, dose-dependent release of Ca++ from SR. Ca++ release induced by δ-HCH is markedly stereoselective. Compared with γ-HCH (50 μM), δ-HCH (50 μM) induces a nearly 20-fold higher initial rate of Ca++ release (4.3 nmol of Ca++/mg/sec). Studies with [3H]ryanodine demonstrate that δ-HCH sharply inhibits Ca++- or daunorubicin-activated radioligand binding (IC50 = 37 and 25 μM, respectively, logit slope = 2). Inhibition of [3H]ryanodine-binding by δ- HCH is stereoselective inasmuch as IC50 values for α, β and γ isomers are >100 μM. The δ-HCH modified Ca++ channel appears to proceed by a noncompetitive mechanism (reducing B(max) in equilibrium experiments) with respect to the conformationally sensitive binding site for [3H]ryanodine. The mechanism is more complex, however, because δ-HCH significantly enhances the observed association rate constant of the remaining sites, and pretreatment of SR induces persistent, concentration-dependent activation or inactivation of [3H]ryanodine-binding sites. The effects of δ-HCH on the ryanodine-sensitive Ca++ channel of cardiac SR is also observed with the brain receptor, suggesting existence of a common mechanism by which chlorinated hydrocarbons can modify Ca++ homeostasis and cell excitability.

AB - δ-Hexachlorocyclohexane (δ-HCH) is shown to be 30-fold more potent as a positive inotropic with rat atrial strips compared with lindane (γ-HCH). Threshold and ED50 values for enhanced contractile force at a pacing frequency of 0.5 Hz are <1 μM and 2.2 μM for δ-HCH and 40 μM and 63 μM for γ-HCH, respectively. Contracture developed in atria exposed to >4 μM δ-HCH (ED50 = 11 μM) but not in atria exposed to γ-HCH. Uptake and release of Ca++ measured from actively loaded cardiac sarcoplasmic reticulum (SR) vesicles is measured with antipyrylazo III. Although δ-HCH (30 μM) decreases Ca++-dependent ATPase by 20%, it does not significantly alter Ca++ loading in the presence of ruthenium red. Addition of δ-HCH (5- 50 μM) after loading is complete causes rapid, dose-dependent release of Ca++ from SR. Ca++ release induced by δ-HCH is markedly stereoselective. Compared with γ-HCH (50 μM), δ-HCH (50 μM) induces a nearly 20-fold higher initial rate of Ca++ release (4.3 nmol of Ca++/mg/sec). Studies with [3H]ryanodine demonstrate that δ-HCH sharply inhibits Ca++- or daunorubicin-activated radioligand binding (IC50 = 37 and 25 μM, respectively, logit slope = 2). Inhibition of [3H]ryanodine-binding by δ- HCH is stereoselective inasmuch as IC50 values for α, β and γ isomers are >100 μM. The δ-HCH modified Ca++ channel appears to proceed by a noncompetitive mechanism (reducing B(max) in equilibrium experiments) with respect to the conformationally sensitive binding site for [3H]ryanodine. The mechanism is more complex, however, because δ-HCH significantly enhances the observed association rate constant of the remaining sites, and pretreatment of SR induces persistent, concentration-dependent activation or inactivation of [3H]ryanodine-binding sites. The effects of δ-HCH on the ryanodine-sensitive Ca++ channel of cardiac SR is also observed with the brain receptor, suggesting existence of a common mechanism by which chlorinated hydrocarbons can modify Ca++ homeostasis and cell excitability.

UR - http://www.scopus.com/inward/record.url?scp=0026713455&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0026713455&partnerID=8YFLogxK

M3 - Article

VL - 262

SP - 661

EP - 669

JO - Journal of Pharmacology and Experimental Therapeutics

JF - Journal of Pharmacology and Experimental Therapeutics

SN - 0022-3565

IS - 2

ER -