Simultaneous recording of intramembrane charge movement components and calcium release in wild-type and S100A1-/- muscle fibres.
In the preceding paper, we reported that flexor digitorum brevis (FDB) muscle fibres from S100A1 knock-out (KO) mice exhibit a selective suppression of the delayed, steeply voltage-dependent component of intra-membrane charge movement current termed Q(gamma). Here, we use 50 microm of the Ca(2+) indicator fluo-4 in the whole cell patch clamp pipette, in addition to 20 mM EGTA and other constituents included for the charge movement studies, and calculate the SR Ca(2+) release flux from the fluo-4 signals during voltage clamp depolarizations. Ca(2+) release flux is decreased in amplitude by the same fraction at all voltages in fibres from S100A1 KO mice compared to fibres from wild-type (WT) littermates, but unchanged in time course at each pulse membrane potential. There is a strong correlation between the time course and magnitude of release flux and the development of Q(gamma). The decreased Ca(2+) release in KO fibres is likely to account for the suppression of Q(gamma) in these fibres. Consistent with this interpretation, 4-chloro-m-cresol (4-CMC; 100 microm) increases the rate of Ca(2+) release and restores Q(gamma) at intermediate depolarizations in fibres from KO mice, but does not increase Ca(2+) release or restore Q(gamma) at large depolarizations. Our findings are consistent with similar activation kinetics for SR Ca(2+) channels in both WT and KO fibres, but decreased Ca(2+) release in the KO fibres possibly due to shorter SR channel open times. The decreased Ca(2+) release at each voltage is insufficient to activate Q(gamma) in fibres lacking S100A1.
Prosser
Benjamin L
BL
Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 108 N. Greene Street, Baltimore, MD 21201, USA.
Hernández-Ochoa
Erick O
EO
Zimmer
Danna B
DB
Schneider
Martin F
MF
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002462:Cell Membrane / Q000502:physiology*; D002478:Cells, Cultured; D015640:Ion Channel Gating; D008564:Membrane Potentials / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D032342:Muscle Cells / Q000502:physiology*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D009418:S100 Proteins / Q000235:genetics / Q000378:metabolism*
D019837:Ryanodine Receptor Calcium Release Channel; D009418:S100 Proteins; C110294:S100A1 protein; D002118:Calcium