Biophysical Journal 71: 908-917 (1996)
© 1996 the Biophysical Society

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Westerblad, H Articles by Allen, D G Search for Related Content PubMed PubMed Citation Articles by Westerblad, H Articles by Allen, D G

Intracellular calibration of the calcium indicator indo-1 in isolated fibers of Xenopus muscle.

Department of Physiology, University of Sydney, Australia. hakan.westerblad@fyfa.ki.se

ABSTRACT

Estimates of the free myoplasmic [Ca2+] ([Ca2+]i) with fluorescent dyes are complicated by the fact that some properties of these dyes are altered in the intracellular environment. In the present study indo-1 was used to measure [Ca2+]i in isolated muscle fibers from Xenopus frogs. Fluorescent ratio signals obtained from indo-1 were converted into [Ca2+]i by means of an intracellular calibration method, which involved microinjection of 0.5 M EGTA and 1 M CaCl2 to get the ratio at very low (Rmin) and high (Rmax) [Ca2+], respectively; ratios at intermediate [Ca2+] were obtained by injection of solutions with different EGTA/Ca(2+)-EGTA proportions. This calibration gave an intracellular Ca2+ dissociation constant of indo-1 of 311 nM and a [Ca2+]i at rest of 52 +/- 4 nM (mean +/- SE; n = 15). Indo-1 records during twitches were compared with records obtained with the much faster indicator mag-indo-1. This analysis suggests a Ca2+ dissociation rate of indo-1 of 52 s-1 (22 degrees C). This makes indo-1 less suitable for measurements of [Ca2+]i during twitches, whereas it is fast enough to follow most aspects of [Ca2+]i during tetani, including the relaxation phase.

This article has been cited by other articles:

				G. Chen, S. Carroll, P. Racay, J. Dick, D. Pette, I. Traub, G. Vrbova, P. Eggli, M. Celio, and B. Schwaller Deficiency in parvalbumin increases fatigue resistance in fast-twitch muscle and upregulates mitochondria Am J Physiol Cell Physiol, July 1, 2001; 281(1): C114 - C122. [Abstract] [Full Text] [PDF]

				N. G. MacFarlane, G. M. Darnley, and G. L. Smith Cellular basis for contractile dysfunction in the diaphragm from a rabbit infarct model of heart failure Am J Physiol Cell Physiol, April 1, 2000; 278(4): C739 - C746. [Abstract] [Full Text] [PDF]

				S. Carroll, P. Nicotera, and D. Pette Calcium transients in single fibers of low-frequency stimulated fast-twitch muscle of rat Am J Physiol Cell Physiol, December 1, 1999; 277(6): C1122 - C1129. [Abstract] [Full Text] [PDF]

				A. Takahashi, P. Camacho, J. D. Lechleiter, and B. Herman Measurement of Intracellular Calcium Physiol Rev, October 1, 1999; 79(4): 1089 - 1125. [Abstract] [Full Text] [PDF]

				B. Schwaller, J. Dick, G. Dhoot, S. Carroll, G. Vrbova, P. Nicotera, D. Pette, A. Wyss, H. Bluethmann, W. Hunziker, et al. Prolonged contraction-relaxation cycle of fast-twitch muscles in parvalbumin knockout mice Am J Physiol Cell Physiol, February 1, 1999; 276(2): C395 - C403. [Abstract] [Full Text] [PDF]