title: Determination of depolarisation- and agonist-evoked calcium fluxes on skeletal muscle cells in primary culture.
abstract: Changes in intracellular calcium concentration ([Ca2+]i) evoked by prolonged depolarisation (120 mM KCl) or by the application of 15 mM caffeine were measured on skeletal muscle cells in primary culture. The extrusion rate (PVmax) of calcium from the myoplasm was determined, which in turn enabled the calculation of the calcium flux (Fl) underlying the measured calcium transients. PVmax was found to increase during differentiation, from 107 +/- 10 microM/s at the early myotube stage to 596 +/- 36 microM/s in secondary myotubes. This was paralleled by a decrease in resting [Ca2+]i from 99 +/- 4 to 51 +/- 2 nM. The depolarisation-evoked Fl rose to peak and then ceased despite the continuous presence of KCl. In contrast, the caffeine-induced Fl showed a peak and a clear steady-level with a peak-to-steady ratio of 5.6 +/- 1.2. Removal of external calcium suppressed the depolarisation--induced flux by 88 +/- 5% indicating that both an influx and a release from the SR underlie the K(+)-evoked calcium transients. Subsequent applications of caffeine resulted in essentially identical fluxes indicating an efficient refilling of the internal stores. Moreover, if a depolarisation-induced calcium transient preceded the second caffeine-evoked release, the latter was significantly larger than the first suggesting that much of the calcium that entered was stored in the SR rather than extruded.
authors.affiliation: Department of Physiology, Research Center for Molecular Medicine, Medical and Health Sciences Centre, University of Debrecen, Hungary.
authors.forename: Henrietta
authors.initials: H
authors.lastname: Szappanos
authors.forename: Julianna
authors.initials: J
authors.lastname: Cseri
authors.forename: Tamás
authors.initials: T
authors.lastname: Deli
authors.forename: László
authors.initials: L
authors.lastname: Kovács
authors.forename: László
authors.initials: L
authors.lastname: Csernoch
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002454:Cell Differentiation; D002478:Cells, Cultured; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D018482:Muscle, Skeletal / Q000166:cytology*; D011188:Potassium / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D032496:Satellite Cells, Skeletal Muscle / Q000378:metabolism
chemical_list: D002110:Caffeine; D011188:Potassium; D002118:Calcium