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Original Article

^a Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085
^b Department of Cellular and Molecular Physiology, Yale University, School of Medicine, New Haven, CT 06520
Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085.(215) 573-5851

baylor{at}mail.med.upenn.edu

Calcium sparks were studied in frog intact skeletal muscle fibers using a home-built confocal scanner whose point-spread function was estimated to be 0.21 µm in x and y and 0.51 µm in z. Observations were made at 17–20°C on fibers from Rana pipiens and Rana temporaria. Fibers were studied in two external solutions: normal Ringer's ([K⁺] = 2.5 mM; estimated membrane potential, –80 to –90 mV) and elevated [K⁺] Ringer's (most frequently, [K⁺] = 13 mM; estimated membrane potential, –60 to –65 mV). The frequency of sparks was 0.04–0.05 sarcomere^–1 s^–1 in normal Ringer's; the frequency increased approximately tenfold in 13 mM [K⁺] Ringer's. Spark properties in each solution were similar for the two species; they were also similar when scanned in the x and the y directions. From fits of standard functional forms to the temporal and spatial profiles of the sparks, the following mean values were estimated for the morphological parameters: rise time, 4 ms; peak amplitude, 1 F/F (change in fluorescence divided by resting fluorescence); decay time constant, 5 ms; full duration at half maximum (FDHM), 6 ms; late offset, 0.01 F/F; full width at half maximum (FWHM), 1.0 µm; mass (calculated as amplitude x 1.206 x FWHM³), 1.3–1.9 µm³. Although the rise time is similar to that measured previously in frog cut fibers (5–6 ms; 17–23°C), cut fiber sparks have a longer duration (FDHM, 9–15 ms), a wider extent (FWHM, 1.3–2.3 µm), and a strikingly larger mass (by 3–10-fold). Possible explanations for the increase in mass in cut fibers are a reduction in the Ca²+ buffering power of myoplasm in cut fibers and an increase in the flux of Ca²+ during release.

Key Words: ryanodine receptors • fluo-3 • confocal microscopy • excitation-contraction coupling • frog muscle

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This article has been cited by other articles:

				W. G. Wier A New View of Ca2+ Sparks in Frog Skeletal Muscle J. Gen. Physiol., December 1, 2001; 118(6): 649 - 652. [Full Text] [PDF]

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