ISSN:
1432-2013
Keywords:
Key words Ca2+
;
Ca2+ -ATPase
;
Caffeine
;
Cardiac
;
Heart
;
Ryanodine
;
Sarcoplasmic reticulum
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract This study was designed to measure the Ca2+ content of rat cardiac sarcoplasmic reticulum (SR) after equilibration with normal diastolic levels of Ca2+ (100 nM), in the absence and presence of caffeine. Measurements of [Ca2+] based on Fura-2 fluorescence were made from a limited bath volume (230 nl) containing individual saponin-permeabilised rat cardiac trabeculae. Injection of caffeine (5–40 mM) into this volume caused an initial release of Ca2+ from the SR, but within 30 s the SR was able to re-accumulate a significant proportion of the Ca2+. Ca2+ re-accumulation into the SR could be prevented by removal of ATP to inhibit the SR Ca2+ pump. Incubation of the preparation in an ATP-containing solution containing caffeine (5–40 mM) and 100 nM Ca2+ indicated that the SR’s ability to retain Ca2+ depends inversely on the dose of caffeine. The relative Ca2+ content of the SR after preincubation with caffeine was 86.7±3.5% at a caffeine concentration of 5 mM, 62.5±5.1% at 10 mM caffeine, 37.8±8.1% at 20 mM caffeine and 7.1±1.9% at 40 mM caffeine. Measurement of the SR Ca2+ release in the presence of different BAPTA concentrations was used to calculate (1) the Ca2+-binding capacity of the preparation (equivalent to 245±10 µM BAPTA) and (2) the Ca2+ content of the SR accessed by caffeine after equilibration with 100 nM Ca2+ (186±11 µmol/l cell volume or 5.6 mmol/l SR volume).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s004240050758
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