Effects of thapsigargin and cyclopiazonic acid on twitch force and sarcoplasmic reticulum Ca2+ content of rabbit ventricular muscle

Stéphane Baudet, Rayan Shaoulian, Donald M Bers

Research output: Contribution to journalArticle

66 Citations (Scopus)

Abstract

Thapsigargin (TG) and cyclopiazonk acid (CPA) are reported to be specific high-affinity inhibitors of the sarcoplasmic reticulum (SR) Ca2+ pump in isolated membranes and cells, with TG causing complete pump inhibition at nanomolar concentrations. To evaluate the effectiveness of TG and CPA in small multicellular cardiac preparations, we used rapid cooling contractures (RCCs) to assess the SR Ca2+ load. In contrast to observations in single myocytes, TG caused remarkably slow and incomplete SR Ca2+ depletion in multicellular preparations. A 45-minute exposure to 500 μM TG at 30°C and 0.5-Hz stimulation only decreased RCCs by 76±5% (and 100 μM CPA reduced RCCs by 59±10% [mean±SEM]). In contrast, 10 minutes with 20 mM caffeine completely abolished RCCs. This confirms that there was still a caffeine-sensitive pool of Ca2+ in the TG-treated muscle. The time constant of rest decay of RCCs was accelerated by both TG (from 83±18 to 26±6 seconds) and CPA (from 68±11 to 10±5 seconds). This might be expected since Ca2+ leaking from the SR during rest cannot be taken back up as efficiently, favoring Ca2+extrusion by the sarcolemmal Na+-Ca2+ exchanger. TG and CPA decreased twitch force (by 44±7% and 40±11%, respectively) and increased twitch duration, presumably because of the SR effects. We conclude that complete blockade of SR Ca2+ uptake by TG or CPA in multicellular preparations cannot be assumed, even at high [TG] or [CPA], unless evaluated (eg, by RCC).

Original languageEnglish (US)
Pages (from-to)813-819
Number of pages7
JournalCirculation Research
Volume73
Issue number5
StatePublished - Nov 1993
Externally publishedYes

Fingerprint

Thapsigargin
Sarcoplasmic Reticulum
Rabbits
Contracture
Muscles
Acids
Caffeine
cyclopiazonic acid
Muscle Cells
Cell Membrane

Keywords

  • Ca-ATPase
  • Excitation-contraction coupling
  • Rapid cooling contractures
  • Sarcoplasmic reticulum

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine

Cite this

Effects of thapsigargin and cyclopiazonic acid on twitch force and sarcoplasmic reticulum Ca2+ content of rabbit ventricular muscle. / Baudet, Stéphane; Shaoulian, Rayan; Bers, Donald M.

In: Circulation Research, Vol. 73, No. 5, 11.1993, p. 813-819.

Research output: Contribution to journalArticle

@article{a0427897f97542a9ba15a127b3058e56,
title = "Effects of thapsigargin and cyclopiazonic acid on twitch force and sarcoplasmic reticulum Ca2+ content of rabbit ventricular muscle",
abstract = "Thapsigargin (TG) and cyclopiazonk acid (CPA) are reported to be specific high-affinity inhibitors of the sarcoplasmic reticulum (SR) Ca2+ pump in isolated membranes and cells, with TG causing complete pump inhibition at nanomolar concentrations. To evaluate the effectiveness of TG and CPA in small multicellular cardiac preparations, we used rapid cooling contractures (RCCs) to assess the SR Ca2+ load. In contrast to observations in single myocytes, TG caused remarkably slow and incomplete SR Ca2+ depletion in multicellular preparations. A 45-minute exposure to 500 μM TG at 30°C and 0.5-Hz stimulation only decreased RCCs by 76±5{\%} (and 100 μM CPA reduced RCCs by 59±10{\%} [mean±SEM]). In contrast, 10 minutes with 20 mM caffeine completely abolished RCCs. This confirms that there was still a caffeine-sensitive pool of Ca2+ in the TG-treated muscle. The time constant of rest decay of RCCs was accelerated by both TG (from 83±18 to 26±6 seconds) and CPA (from 68±11 to 10±5 seconds). This might be expected since Ca2+ leaking from the SR during rest cannot be taken back up as efficiently, favoring Ca2+extrusion by the sarcolemmal Na+-Ca2+ exchanger. TG and CPA decreased twitch force (by 44±7{\%} and 40±11{\%}, respectively) and increased twitch duration, presumably because of the SR effects. We conclude that complete blockade of SR Ca2+ uptake by TG or CPA in multicellular preparations cannot be assumed, even at high [TG] or [CPA], unless evaluated (eg, by RCC).",
keywords = "Ca-ATPase, Excitation-contraction coupling, Rapid cooling contractures, Sarcoplasmic reticulum",
author = "St{\'e}phane Baudet and Rayan Shaoulian and Bers, {Donald M}",
year = "1993",
month = "11",
language = "English (US)",
volume = "73",
pages = "813--819",
journal = "Circulation Research",
issn = "0009-7330",
publisher = "Lippincott Williams and Wilkins",
number = "5",

}

TY - JOUR

T1 - Effects of thapsigargin and cyclopiazonic acid on twitch force and sarcoplasmic reticulum Ca2+ content of rabbit ventricular muscle

AU - Baudet, Stéphane

AU - Shaoulian, Rayan

AU - Bers, Donald M

PY - 1993/11

Y1 - 1993/11

N2 - Thapsigargin (TG) and cyclopiazonk acid (CPA) are reported to be specific high-affinity inhibitors of the sarcoplasmic reticulum (SR) Ca2+ pump in isolated membranes and cells, with TG causing complete pump inhibition at nanomolar concentrations. To evaluate the effectiveness of TG and CPA in small multicellular cardiac preparations, we used rapid cooling contractures (RCCs) to assess the SR Ca2+ load. In contrast to observations in single myocytes, TG caused remarkably slow and incomplete SR Ca2+ depletion in multicellular preparations. A 45-minute exposure to 500 μM TG at 30°C and 0.5-Hz stimulation only decreased RCCs by 76±5% (and 100 μM CPA reduced RCCs by 59±10% [mean±SEM]). In contrast, 10 minutes with 20 mM caffeine completely abolished RCCs. This confirms that there was still a caffeine-sensitive pool of Ca2+ in the TG-treated muscle. The time constant of rest decay of RCCs was accelerated by both TG (from 83±18 to 26±6 seconds) and CPA (from 68±11 to 10±5 seconds). This might be expected since Ca2+ leaking from the SR during rest cannot be taken back up as efficiently, favoring Ca2+extrusion by the sarcolemmal Na+-Ca2+ exchanger. TG and CPA decreased twitch force (by 44±7% and 40±11%, respectively) and increased twitch duration, presumably because of the SR effects. We conclude that complete blockade of SR Ca2+ uptake by TG or CPA in multicellular preparations cannot be assumed, even at high [TG] or [CPA], unless evaluated (eg, by RCC).

AB - Thapsigargin (TG) and cyclopiazonk acid (CPA) are reported to be specific high-affinity inhibitors of the sarcoplasmic reticulum (SR) Ca2+ pump in isolated membranes and cells, with TG causing complete pump inhibition at nanomolar concentrations. To evaluate the effectiveness of TG and CPA in small multicellular cardiac preparations, we used rapid cooling contractures (RCCs) to assess the SR Ca2+ load. In contrast to observations in single myocytes, TG caused remarkably slow and incomplete SR Ca2+ depletion in multicellular preparations. A 45-minute exposure to 500 μM TG at 30°C and 0.5-Hz stimulation only decreased RCCs by 76±5% (and 100 μM CPA reduced RCCs by 59±10% [mean±SEM]). In contrast, 10 minutes with 20 mM caffeine completely abolished RCCs. This confirms that there was still a caffeine-sensitive pool of Ca2+ in the TG-treated muscle. The time constant of rest decay of RCCs was accelerated by both TG (from 83±18 to 26±6 seconds) and CPA (from 68±11 to 10±5 seconds). This might be expected since Ca2+ leaking from the SR during rest cannot be taken back up as efficiently, favoring Ca2+extrusion by the sarcolemmal Na+-Ca2+ exchanger. TG and CPA decreased twitch force (by 44±7% and 40±11%, respectively) and increased twitch duration, presumably because of the SR effects. We conclude that complete blockade of SR Ca2+ uptake by TG or CPA in multicellular preparations cannot be assumed, even at high [TG] or [CPA], unless evaluated (eg, by RCC).

KW - Ca-ATPase

KW - Excitation-contraction coupling

KW - Rapid cooling contractures

KW - Sarcoplasmic reticulum

UR - http://www.scopus.com/inward/record.url?scp=0027525079&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0027525079&partnerID=8YFLogxK

M3 - Article

VL - 73

SP - 813

EP - 819

JO - Circulation Research

JF - Circulation Research

SN - 0009-7330

IS - 5

ER -