Calcium signals recorded from cut frog twitch fibers containing antipyrylazo III

James Maylie, M. Irving, N. L. Sizto, W. K. Chandler

Research output: Contribution to journalArticle

50 Citations (Scopus)

Abstract

The Ca indicator antipyrylazo III was introduced into cut frog twitch fibers by diffusion. Like arsenazo III, antipyrylazo III was largely bound to or sequestered by intracellular constituents; on average, a fraction 0.68 was so immobilized. After action potential stimulation, there was an early change in absorbance, with a wavelength dependence that nearly matched a cuvette Ca-difference spectrum. As with arsenazo III, this signal became prolonged as experiments progressed. In a freshly prepared cut fiber containing 0.3 mM indicator, the absorbance change had an average half-width of 10 ms at 18° C. The peak amplitude of this Ca signal depended on the indicator concentration in a roughly parabolic manner, which is consistent with a 1:2 stoichiometry for Ca:indicator complexation and, for indicator concentrations ≤ 0.4 mM, constant peak free [Ca]. If all the antipyrylazo III inside a fiber can react normally with Ca, peak free [Ca] is 3 μM at 18°C. If only freely diffusible indicator can react, the estimate is 42 μM. The true amplitude probably lies somewhere in between. The time course of Ca binding to intracellular buffers and of Ca release from the sarcoplasmic reticulum is estimated from the 3- and 42-μM myoplasmic [Ca] transients. After action potential stimulation, the release waveform is rapid and brief; its latency after the surface action potential is 2-3 ms and its half-width is 2-4 ms. This requires rapid coupling between the action potential in the transverse tubular system and Ca release from the sarcoplasmic reticulum. The peak fraction occupancy calculated for Ca-regulatory sites on troponin is 0.46 for the 3-μM transient and 0.93 for the 42-μM transient. During a 100-ms tetanus at 100 Hz, the corresponding fractional occupancies are 0.56 and 0.94. The low value of occupancy associated with the low-amplitude [Ca] calibration seems inconsistent with a brief tetanus being able to produce near-maximal activation.

Original languageEnglish (US)
Pages (from-to)83-143
Number of pages61
JournalJournal of General Physiology
Volume89
Issue number1
StatePublished - 1987
Externally publishedYes

Fingerprint

Anura
Action Potentials
Arsenazo III
Calcium
Tetanus
Sarcoplasmic Reticulum
Troponin
Calibration
Buffers
antipyrylazo III

ASJC Scopus subject areas

  • Physiology

Cite this

Calcium signals recorded from cut frog twitch fibers containing antipyrylazo III. / Maylie, James; Irving, M.; Sizto, N. L.; Chandler, W. K.

In: Journal of General Physiology, Vol. 89, No. 1, 1987, p. 83-143.

Research output: Contribution to journalArticle

Maylie, James ; Irving, M. ; Sizto, N. L. ; Chandler, W. K. / Calcium signals recorded from cut frog twitch fibers containing antipyrylazo III. In: Journal of General Physiology. 1987 ; Vol. 89, No. 1. pp. 83-143.
@article{51d64a0f95d34e4c800700ea504aa6b4,
title = "Calcium signals recorded from cut frog twitch fibers containing antipyrylazo III",
abstract = "The Ca indicator antipyrylazo III was introduced into cut frog twitch fibers by diffusion. Like arsenazo III, antipyrylazo III was largely bound to or sequestered by intracellular constituents; on average, a fraction 0.68 was so immobilized. After action potential stimulation, there was an early change in absorbance, with a wavelength dependence that nearly matched a cuvette Ca-difference spectrum. As with arsenazo III, this signal became prolonged as experiments progressed. In a freshly prepared cut fiber containing 0.3 mM indicator, the absorbance change had an average half-width of 10 ms at 18° C. The peak amplitude of this Ca signal depended on the indicator concentration in a roughly parabolic manner, which is consistent with a 1:2 stoichiometry for Ca:indicator complexation and, for indicator concentrations ≤ 0.4 mM, constant peak free [Ca]. If all the antipyrylazo III inside a fiber can react normally with Ca, peak free [Ca] is 3 μM at 18°C. If only freely diffusible indicator can react, the estimate is 42 μM. The true amplitude probably lies somewhere in between. The time course of Ca binding to intracellular buffers and of Ca release from the sarcoplasmic reticulum is estimated from the 3- and 42-μM myoplasmic [Ca] transients. After action potential stimulation, the release waveform is rapid and brief; its latency after the surface action potential is 2-3 ms and its half-width is 2-4 ms. This requires rapid coupling between the action potential in the transverse tubular system and Ca release from the sarcoplasmic reticulum. The peak fraction occupancy calculated for Ca-regulatory sites on troponin is 0.46 for the 3-μM transient and 0.93 for the 42-μM transient. During a 100-ms tetanus at 100 Hz, the corresponding fractional occupancies are 0.56 and 0.94. The low value of occupancy associated with the low-amplitude [Ca] calibration seems inconsistent with a brief tetanus being able to produce near-maximal activation.",
author = "James Maylie and M. Irving and Sizto, {N. L.} and Chandler, {W. K.}",
year = "1987",
language = "English (US)",
volume = "89",
pages = "83--143",
journal = "Journal of General Physiology",
issn = "0022-1295",
publisher = "Rockefeller University Press",
number = "1",

}

TY - JOUR

T1 - Calcium signals recorded from cut frog twitch fibers containing antipyrylazo III

AU - Maylie, James

AU - Irving, M.

AU - Sizto, N. L.

AU - Chandler, W. K.

PY - 1987

Y1 - 1987

N2 - The Ca indicator antipyrylazo III was introduced into cut frog twitch fibers by diffusion. Like arsenazo III, antipyrylazo III was largely bound to or sequestered by intracellular constituents; on average, a fraction 0.68 was so immobilized. After action potential stimulation, there was an early change in absorbance, with a wavelength dependence that nearly matched a cuvette Ca-difference spectrum. As with arsenazo III, this signal became prolonged as experiments progressed. In a freshly prepared cut fiber containing 0.3 mM indicator, the absorbance change had an average half-width of 10 ms at 18° C. The peak amplitude of this Ca signal depended on the indicator concentration in a roughly parabolic manner, which is consistent with a 1:2 stoichiometry for Ca:indicator complexation and, for indicator concentrations ≤ 0.4 mM, constant peak free [Ca]. If all the antipyrylazo III inside a fiber can react normally with Ca, peak free [Ca] is 3 μM at 18°C. If only freely diffusible indicator can react, the estimate is 42 μM. The true amplitude probably lies somewhere in between. The time course of Ca binding to intracellular buffers and of Ca release from the sarcoplasmic reticulum is estimated from the 3- and 42-μM myoplasmic [Ca] transients. After action potential stimulation, the release waveform is rapid and brief; its latency after the surface action potential is 2-3 ms and its half-width is 2-4 ms. This requires rapid coupling between the action potential in the transverse tubular system and Ca release from the sarcoplasmic reticulum. The peak fraction occupancy calculated for Ca-regulatory sites on troponin is 0.46 for the 3-μM transient and 0.93 for the 42-μM transient. During a 100-ms tetanus at 100 Hz, the corresponding fractional occupancies are 0.56 and 0.94. The low value of occupancy associated with the low-amplitude [Ca] calibration seems inconsistent with a brief tetanus being able to produce near-maximal activation.

AB - The Ca indicator antipyrylazo III was introduced into cut frog twitch fibers by diffusion. Like arsenazo III, antipyrylazo III was largely bound to or sequestered by intracellular constituents; on average, a fraction 0.68 was so immobilized. After action potential stimulation, there was an early change in absorbance, with a wavelength dependence that nearly matched a cuvette Ca-difference spectrum. As with arsenazo III, this signal became prolonged as experiments progressed. In a freshly prepared cut fiber containing 0.3 mM indicator, the absorbance change had an average half-width of 10 ms at 18° C. The peak amplitude of this Ca signal depended on the indicator concentration in a roughly parabolic manner, which is consistent with a 1:2 stoichiometry for Ca:indicator complexation and, for indicator concentrations ≤ 0.4 mM, constant peak free [Ca]. If all the antipyrylazo III inside a fiber can react normally with Ca, peak free [Ca] is 3 μM at 18°C. If only freely diffusible indicator can react, the estimate is 42 μM. The true amplitude probably lies somewhere in between. The time course of Ca binding to intracellular buffers and of Ca release from the sarcoplasmic reticulum is estimated from the 3- and 42-μM myoplasmic [Ca] transients. After action potential stimulation, the release waveform is rapid and brief; its latency after the surface action potential is 2-3 ms and its half-width is 2-4 ms. This requires rapid coupling between the action potential in the transverse tubular system and Ca release from the sarcoplasmic reticulum. The peak fraction occupancy calculated for Ca-regulatory sites on troponin is 0.46 for the 3-μM transient and 0.93 for the 42-μM transient. During a 100-ms tetanus at 100 Hz, the corresponding fractional occupancies are 0.56 and 0.94. The low value of occupancy associated with the low-amplitude [Ca] calibration seems inconsistent with a brief tetanus being able to produce near-maximal activation.

UR - http://www.scopus.com/inward/record.url?scp=0023146373&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0023146373&partnerID=8YFLogxK

M3 - Article

VL - 89

SP - 83

EP - 143

JO - Journal of General Physiology

JF - Journal of General Physiology

SN - 0022-1295

IS - 1

ER -