Effect of fura-2 on action potential-stimulated calcium release in cut twitch fibers from frog muscle.
Cut fibers (striation spacing, 3.6-4.2 microns) were mounted in a double Vaseline-gap chamber and studied at 14-15 degrees C. One or both of the Ca indicators fura-2 and purpurate-3,3' diacetic acid (PDAA) were introduced into the optical recording site by diffusion from the end pools. Sarcoplasmic reticulum (SR) Ca release was elicited by action potential stimulation. With resting [fura-2] = 0 mM at the optical site, the [Ca] transient measured with PDAA was used to estimate SR Ca release (Baylor, S.M., W.K. Chandler, and M.W. Marshall. 1983. Journal of Physiology. 344:625-666). With resting [fura-2] > 0 mM, the contribution from Ca complexation by fura-2 was added to the estimate. When resting [fura-2] was increased from 0 to 0.5-2 mM, both the amount of SR Ca release and the maximal rate of release were increased by approximately 20%. These results are qualitatively similar to those obtained in intact fibers (Baylor, S.M., and S. Hollingworth. 1988. Journal of Physiology. 403:151-192; Hollingworth, S., A. B. Harkins, N. Kurebayashi, M. Konishi, and S. M. Baylor. 1992. Biophysical Journal. 63:224-234) and are consistent with a reduction of Ca inactivation of SR Ca release produced by 0.5-2 mM fura-2. With resting [fura-2] > or = 2 mM, the PDAA [Ca] transient was reduced to nearly zero and SR Ca release could be estimated from delta [Cafura-2] alone. When resting [fura-2] was increased from 2-4 to 5-6 mM, both the amount of SR Ca release and the maximal rate of release were decreased by approximately half, consistent with a possible reduction of Ca-induced Ca release (Jacquemond, V., L. Csernoch, M. G. Klein, and M. F. Schneider. 1991. Biophysical Journal. 60:867-873) or a possible pharmacological effect of fura-2.
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Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510-8026.
Jong
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Chandler
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Baylor
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D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D016257:Fura-2 / Q000494:pharmacology*; D007202:Indicators and Reagents; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D009114:Murexide / Q000031:analogs & derivatives / Q000494:pharmacology; D009132:Muscles / Q000378:metabolism* / Q000502:physiology; D011896:Rana temporaria / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000737:chemistry / Q000378:metabolism / Q000502:physiology
D007202:Indicators and Reagents; C062372:purpurate-3,3'-diacetic acid; D009114:Murexide; D002118:Calcium; D016257:Fura-2