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Unitat de Fisiologia Animal, Departamento de Biologia Cellular, Fisiologia i Immunología, Facultat de Ciencies, Universitat Autonoma de Barcelona, 08193 Cerdanyola, Barcelona, Spain
The effect of
temperature on sarcoplasmic reticulum (SR) Ca2+ uptake and
release was measured in trout atrial myocytes using the perforated
patch-clamp technique. Depolarization of the myocyte for 10 s to
different membrane potentials (Vm) induced SR
Ca2+ uptake. The relationship between
Vm and SR Ca2+ uptake was not
significantly changed by lowering the experimental temperature from 21 to 7°C, and the relationship between total cytosolic Ca2+
and SR Ca2+ uptake was similar at the two temperatures with
a pooled Vmax = 66 amol/pF and
K0.5 = 4 amol/pF. Quantification of the
Ca2+ release from the SR elicited by 10-ms depolarizations
to different Vm showed an increasing SR
Ca2+ release at more positive Vm
between 
50 and +10 mV, whereas SR Ca2+ release stagnated
between +10 and +50 mV. Lowering of the temperature did not affect this
relationship significantly, giving an SR Ca2+ release of
1.71 and 1.54 amol/pF at 21 and 7°C, respectively. Furthermore,
clearance of the SR Ca2+ content slowed down inactivation
of the L-type Ca2+ current at both temperatures (the fast
time constant increased significantly from 10.4 ± 1.9 to
15.0 ± 2.0 ms at 21°C and from 38 ± 15 to 73 ± 24 ms at 7°C). Thus the SR has the capacity to remove the entire
Ca2+ transient at physiologically relevant stimulation
frequencies at both 21 and 7°C, although it is estimated that ~40%
of the total Ca2+ transient is liberated from and reuptaken
by the SR with continuous stimulation at 0.5 Hz independently of the
experimental temperature.
sodium/calcium exchange; calcium current; excitation-contraction coupling; teleost heart; caffeine
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