Calcium signals recorded from cut frog twitch fibers containing tetramethylmurexide

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

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

The Ca indicator tetramethylmurexide was introduced into cut fibers, mounted in a double-Vaseline-gap chamber, by diffusion from the end-pool solutions. The indicator diffused rapidly to the central region of a fiber where optical recording was done and, if removed, diffused away equally fast. The time course of concentration suggests that, on average, a fraction 0.27 of indicator was reversibly bound to myoplasmic constituents and the free diffusion constant was 1.75 x 10-6 cm2/s at 18°C. The shape of the resting absorbance spectrum suggests that a fraction 0.11-0.15 of tetramethylmurexide inside a fiber was complexed with Ca. After action potential stimulation, there was a rapid transient change in indicator absorbance followed by a maintained change of opposite sign. The wavelenth dependence of both changes matched a cuvette Ca-difference spectrum. The amplitude of the early peak varied linearly with indicator concentration and corresponded to an average rise in free [Ca] of 17 μM. These rather diverse findings can be explained if the sarcoplasmic reticulum membranes are permeable to Ca-free indicator. Both Ca-free and Ca-complexed indicator inside the sarcoplasmic reticulum would appear to be bound by diffusion analysis and the Ca-complexed form would be detected by the resting absorbance spectrum. The transient change in indicator absorbance would be produced by myoplasmic Ca reacting with indicator molecules that freely diffuse in myoplasmic solution. The maintained signal, which reports Ca dissociating from indicator complexed at rest, would come from changes within the sarcoplasmic reticulum. A method, based on these ideas, is described for separating the two components of the tetramethylmurexide signal. The estimated myoplasmic free [Ca] transient has an average peak value of 26 μM at 18°C. Its time course is similar to, but possibly faster than, that recorded with antipyrylazo III.

Original languageEnglish (US)
Pages (from-to)145-176
Number of pages32
JournalJournal of General Physiology
Volume89
Issue number1
DOIs
StatePublished - 1987
Externally publishedYes

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Sarcoplasmic Reticulum
Anura
Calcium
Petrolatum
Optical Fibers
Action Potentials
Membranes
tetramethylmurexide

ASJC Scopus subject areas

  • Physiology

Cite this

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

In: Journal of General Physiology, Vol. 89, No. 1, 1987, p. 145-176.

Research output: Contribution to journalArticle

Maylie, James ; Irving, M. ; Sizto, N. L. ; Boyarsky, G. ; Chandler, W. K. / Calcium signals recorded from cut frog twitch fibers containing tetramethylmurexide. In: Journal of General Physiology. 1987 ; Vol. 89, No. 1. pp. 145-176.
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