title: Repriming and activation alter the frequency of stereotyped discrete Ca2+ release events in frog skeletal muscle.
abstract: 1. Brief localized elevations in myoplasmic [Ca2+] (Ca2+ sparks) in individual sarcomeres of voltage-clamped frog skeletal muscle fibres were examined by laser scanning confocal microscopy. 2. Fibres held at 0 mV were briefly repolarized to -90 mV (repriming pulse) to restore only a small fraction of sarcoplasmic reticulum (SR) calcium release. Subsequent depolarization to 0 mV (test pulse) caused the appearance of small numbers of Ca2+ sparks at different sarcomeres from pulse to pulse. Increasing the repriming time resulted in an increase in the frequency of occurrence of the Ca2+ sparks. 3. The amplitude and spatio-temporal extent of the Ca2+ sparks were independent of the repriming time and test pulse voltage. Ca2+ sparks recorded during small depolarizations of fibres held at -90 mV had a similar amplitude and spatio-temporal extent as those recorded after brief repriming of the same fibre held at 0 mV. 4. We conclude that stereotyped Ca2+ sparks underlie calcium release at all voltages and all extents of repriming. The amplitude of Ca2+ release is thus graded by the frequency but not by the amplitude or spatio-temporal extent of the individual SR Ca2+ release events.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore 21201, USA.
authors.forename: A
authors.initials: A
authors.lastname: Lacampagne
authors.forename: W J
authors.initials: WJ
authors.lastname: Lederer
authors.forename: M F
authors.initials: MF
authors.lastname: Schneider
authors.forename: M G
authors.initials: MG
authors.lastname: Klein
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004594:Electrophysiology; D018613:Microscopy, Confocal; D018482:Muscle, Skeletal / Q000378:metabolism*; D011894:Rana pipiens; D012518:Sarcomeres / Q000378:metabolism
chemical_list: D002118:Calcium