The contribution of the sarcoplasmic reticulum Ca2+-transport ATPase to caffeine-induced Ca2+ transients of murine skinned skeletal muscle fibres |
| |
Authors: | Makoto Makabe Oliver Werner Rainer H A Fink |
| |
Institution: | (1) II. Institute of Physiology, University of Heidelberg, INF 326, D-69120 Heidelberg, Germany, DE;(2) Deutsches Krebsforschungszentrum, Division of Medical and Biological Informatics, INF 280, D-69120 Heidelberg, Germany, DE |
| |
Abstract: | The present study was carried out to investigate the contribution of the Ca2+-transport ATPase of the sarcoplasmic reticulum (SR) to caffeine-induced Ca2+ release in skinned skeletal muscle fibres. Chemically skinned fibres of balb-C-mouse EDL (extensor digitorum longus) were
exposed for 1 min to a free Ca2+ concentration of 0.36 μM to load the SR with Ca2+. Release of Ca2+ from the SR was induced by 30 mM caffeine and recorded as an isometric force transient. For every preparation a pCa/force
relationship was constructed, where pCa = −log10 Ca2+]. In a new experimental approach, we used the pCa/force relationship to transform each force transient directly into a Ca2+ transient. The calculated Ca2+ transients were fitted by a double exponential function: Y
0 + A
1⋅exp (−t/t
1) + A
2⋅exp(t/t
2), with A
1 < 0 < A
2, t
1 < t
2 and Y
0, A
1, A
2 in micromolar. Ca2+ transients in the presence of the SR Ca2+-ATPase inhibitor cyclopiazonic acid (CPA) were compared to those obtained in the absence of the drug. We found that inhibition
of the SR Ca2+-ATPase during caffeine-induced Ca2+ release causes an increase in the peak Ca2+ concentration in comparison to the control transients. Increasing CPA concentrations prolonged the time-to-peak in a dose-dependent
manner, following a Hill curve with a half-maximal value of 6.5 ± 3 μM CPA and a Hill slope of 1.1 ± 0.2, saturating at 100 μM.
The effects of CPA could be simulated by an extended three-compartment model representing the SR, the myofilament space and
the external bathing solution. In terms of this model, the SR Ca2+-ATPase influences the Ca2+ gradient across the SR membrane in particular during the early stages of the Ca2+ transient, whereas the subsequent relaxation is governed by diffusional loss of Ca2+ into the bathing solution.
Received: 2 February 1996/Accepted: 1 April 1996 |
| |
Keywords: | Sarcoplasmic reticulum SR Ca2+-transport ATPase Cyclopiazonic acid Mouse muscle Skinned fibres Caffeine |
本文献已被 SpringerLink 等数据库收录! |
|