First published online March 9, 2004
Journal of Experimental Biology 207, 1369-1377 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00884
Effect of ß-adrenergic stimulation on the relationship between membrane potential, intracellular [Ca2+] and sarcoplasmic reticulum Ca2+ uptake in rainbow trout atrial myocytes
Anna Llach*,1,
Jingbo Huang*,2,
Franklin Sederat2,
Lluis Tort1,
Glen Tibbits2 and
Leif Hove-Madsen1,
1 Unitat de Fisiologia Animal, Departamento de Biologia Celular, Fisiologia
i Immunología, Facultat de Ciencies, Universitat Autònoma de
Barcelona, 08193, Cerdanyola, Barcelona, España
2 Cardiac Membrane Research Laboratory, Department of Kinesiology, Simon
Fraser University, Burnaby, BC, Canada, V5A 1S6
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Fig. 4. Effect of isoproterenol (ISO) on ICa and Ca2+
transient. (A) ICa elicited by repetitive 200 ms depolarizations
(0.2 Hz) to 0 mV in the absence (black line) and presence (gray line) of 1
µmol l–1 ISO. (B) Ca2+ transients recorded
simultaneously with ICa in A. Traces are averages of recordings
from 7 cells at steady state. Filled symbols + solid line, no ISO; gray
symbols + dotted line, + ISO.
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Fig. 5. Effect of ISO on Ca2+ transient and whole membrane current
during long depolarizations. (A) The top panel shows the stimulation protocol;
the resulting Ca2+ transients are shown below in the absence (black
line) or the presence (gray line) of 1 µmol l–1
isoproterenol (ISO). (B) Simultaneous recordings of whole membrane current.
The time scales corresponds to 5 s (left) and 4 s (right). (C) Simultaneous
recordings of Ca2+ transients and membrane currents during a rapid
caffeine application in control, with 1 µmol l–1 ISO and
after washout of ISO. Notice that the effects of ISO on both Ca2+
transient and membrane current were fully reversible.
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Fig. 6. Effect of ISO on the relationship between SR Ca2+ uptake and the
[Ca2+]i. (A) Representative intracellular
Ca2+ recordings in control and with 1 µmol l–1
isoproterenol (ISO). Bars above traces indicate membrane potential (top bar)
and extracellular solution (lower bar); –, regular bath solution; +,
bath solution with 10 mmol l–1 caffeine. (B) Effect of
membrane potential on the average Ca2+ transient during
depolarization (black bars) and the peak Ca2+ transient elicited by
10 mmol l–1 Caf (white bars, N=7). (C) Effect of ISO
on the relationship between SR Ca2+ uptake rate and
[Ca2+]i (N=7). Solid (control) and dotted (ISO)
lines represent fits of data with a Hill equation.
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Fig. 7. Comparison of SR Ca2+ uptake and sarcolemmal Ca2+
extrusion. (A) Total amount of Ca2+ taken up by the SR, sarcolemmal
Ca2+ extrusion (SL) and the sum of the two (TOT) in the absence
(black bars) and the presence of 1 µmol l–1 isoproterenol
(gray bars). (B) The relative contribution of the SR Ca2+ uptake
(SR/TOT) and sarcolemmal Ca2+ extrusion (SL/TOT) to the total
Ca2+ elimination from the cytosol during a contraction elicited by
a 200 ms depolarization. SR Ca2+ uptake was calculated using
individual Ca2+ transients from the 7 experiments in
Fig. 4B and the relationship
between [Ca2+]i and SR Ca2+ uptake in
Fig. 6C. Sarcolemmal
Ca2+ extrusion was obtained from the time integral of the tail
currents in the corresponding 7 cells in
Fig. 4A. Significant
differences: ** (P<0.01, N=7) and ***
(P<0.001, N=7).
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Fig. 1. Experimental protocol. SR Ca2+ uptake was measured by clearance
of the SR Ca2+ content by a brief exposure to 10 mmol
l–1 caffeine (Caf) at –80 mV (Clear). The SR was then
loaded during a 3 or 10 s depolarization (Load). The SR Ca2+ uptake
during the depolarization to different membrane potentials
(Vm) was quantified as the Caf releasable Ca2+
content and obtained by integration of the INCX elicited by Caf
(Release).
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Fig. 3. Relationship between SR Ca2+ loading and membrane potential. The
Caf releasable SR Ca2+ content was plotted as a function of the
membrane potential Vm of the preceding depolarization in
the absence (CON; filled symbols) or the presence of 1 µmol
l–1 isoproterenol (ISO; open symbols). Data (N=6)
were fit with a Boltzmann equation. Arrows indicate the
K0.5 without (solid) and with ISO (broken line).
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Fig. 9. Relationship between SR Ca2+ loading and membrane potential in
control (filled circles) or with isoproterenol (ISO) + low extracellular
[Ca2+] (open circles). ISO + low [Ca2+] significantly
affected the relationship (P<0.001, N=5). Asterisks
denote a significant (P<0.001) difference between control and ISO
+ low [Ca2+].
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Fig. 2. Effect of isoproterenol (ISO) on SR Ca2+ uptake. (A)
INCX elicited by 10 mmol l–1 Caffeine after a
preceding 10 s depolarization to –70, –30 or –10 mV in the
absence (CON) and the presence of 1 µmol l–1 ISO. (B) Time
integrals of the currents in A. The experimental conditions are indicated
above each trace and the time scale bar corresponds to 5 s.
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Fig. 8. Effect of isoproterenol (ISO) in the presence of low extracellular
[Ca2+]. (A) Representative ICa recordings in control
(CON) and with 1 µmol l–1 ISO + low extracellular
[Ca2+] (ISO + low Ca2+). (B) Corresponding recordings of
Caf releasable SR Ca2+ load after a 10 s depolarization to
–30, –10 or +10 mV.
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© The Company of Biologists Ltd 2004
