Influx of extracellular Ca$^2+$ plays a major role in the activation
of contraction in fish cardiac cells. The relative contributions
of Na$^+$/Ca$^2+$ exchange and L-type Ca$^2+$ channels
to Ca$^2+$ influx are, however, unknown. Using a physiological
action potential as the command pulse in voltage-clamped heart cells,
we examined sarcolemmal Ca$^2+$ influx through Na$^+$/Ca$^2+$
exchange and L-type Ca$^2+$ channels in crucian carp (Carassius
carassius L.) ventricular myocytes. When other cation conductances
were blocked, a Ni2+-sensitive current with the characteristic voltage-
and time-dependent properties of the Na$^+$/Ca$^2+$ exchange
current could be distinguished. At the maximum overshoot voltage
of the ventricular action potential (+40 mV; Na$^+$i=10 mmol
l-1), the density of the Na$^+$/Ca$^2+$ exchange current
was 2.99+/-0.27 pA pF-1 for warm-acclimated fish (23 degrees C) and
2.38+/-0.42 pA pF-1 for cold-acclimated fish (4 degrees C) (means
+/- s.e.m., N=5-6; not significantly different, P=0.26). The relative
contributions of the Na$^+$/Ca$^2+$ exchanger and L-type
Ca$^2+$ channels to Ca$^2+$ influx were estimated using two
partly different methods. Integration of the Ni2+-sensitive Na$^+$/Ca$^2+$
exchange current and the verapamil- and Cd2+-sensitive L-type Ca$^2+$
current suggests that, during the action potential, approximately
one-third of the activating Ca$^2+$ comes through Na$^+$/Ca$^2+$
exchange and approximately two-thirds through L-type Ca$^2+$
channels. An alternative method of analysis, using the inward tail
current as a measure of the total sarcolemmal Ca$^2+$ flux from
which the Ni2+-sensitive Na$^+$/Ca$^2+$ exchange current
was subtracted to obtain the Ca$^2+$ influx through the channels,
suggests that L-type Ca$^2+$ channels and Na$^+$/Ca$^2+$
exchange are almost equally important in the activation of contraction.
Furthermore, the time course of cell shortening is not adequately
explained by sarcolemmal Ca$^2+$ influx through the channels
alone, but is well approximated by the sum of Ca$^2+$ influx
through the channels and the exchanger. The present results indicate
that reverse Na$^+$/Ca$^2+$ exchange in crucian carp ventricular
myocytes has sufficient capacity to trigger contraction and suggest
that the exchange current makes a significant contribution to contractile
Ca$^2+$ during the physiological action potential. The relative
significance of channels and exchanger molecules in sarcolemmal Ca$^2+$
entry into crucian carp ventricular myocytes was unaffected by thermal
acclimation when determined at 22 degrees C.
%0 Journal Article
%1 Vorn_1999_1763
%A Vornanen, M
%D 1999
%J J. Exp. Biol.
%K 0010359679 ATPase, Acids, Acute Adaptation, Adenosine, Adolescent, Adult, Aged, Agents, Agonists, Animals, Anoxia, Anti-Bacterial Atrial Biopsy, Carbachol, Cardiotonic Cardiovascular Carps, Child, Chronic Contraction, Cyanide, Diagnosis, Differential, Disease, Distribution, Ear Ear, Electrophysiology, Europe, Fast-Twitch, Fatty Female, Fibers, Follow-Up Function, Gov't, Heart Hodgkin Humans, In Incidence, Lymphoma, Male, Media, Membranes, Middle Middle, Muscarine, Muscarinic Muscle Myocardial Needle, Neoplasms, Non-Hodgkin, Non-U.S. Otitis Outcome, Parvalbumins, Physiological, Preschool, Purines, Rate, Registries, Relaxation, Research Reticulum, Rhabdomyosarcoma, Sarcoplasmic Sex Sodium Studies, Support, Temperature, Treatment Ventricular Vitro, {C}a$^{2+}$-Transporting
%P 1763-75
%T Na$^+$/Ca$^2+$ exchange current in ventricular myocytes of
fish heart: contribution to sarcolemmal Ca$^2+$ influx
%U http://jeb.biologists.org/cgi/reprint/202/13/1763
%V 202 (Pt 13)
%X Influx of extracellular Ca$^2+$ plays a major role in the activation
of contraction in fish cardiac cells. The relative contributions
of Na$^+$/Ca$^2+$ exchange and L-type Ca$^2+$ channels
to Ca$^2+$ influx are, however, unknown. Using a physiological
action potential as the command pulse in voltage-clamped heart cells,
we examined sarcolemmal Ca$^2+$ influx through Na$^+$/Ca$^2+$
exchange and L-type Ca$^2+$ channels in crucian carp (Carassius
carassius L.) ventricular myocytes. When other cation conductances
were blocked, a Ni2+-sensitive current with the characteristic voltage-
and time-dependent properties of the Na$^+$/Ca$^2+$ exchange
current could be distinguished. At the maximum overshoot voltage
of the ventricular action potential (+40 mV; Na$^+$i=10 mmol
l-1), the density of the Na$^+$/Ca$^2+$ exchange current
was 2.99+/-0.27 pA pF-1 for warm-acclimated fish (23 degrees C) and
2.38+/-0.42 pA pF-1 for cold-acclimated fish (4 degrees C) (means
+/- s.e.m., N=5-6; not significantly different, P=0.26). The relative
contributions of the Na$^+$/Ca$^2+$ exchanger and L-type
Ca$^2+$ channels to Ca$^2+$ influx were estimated using two
partly different methods. Integration of the Ni2+-sensitive Na$^+$/Ca$^2+$
exchange current and the verapamil- and Cd2+-sensitive L-type Ca$^2+$
current suggests that, during the action potential, approximately
one-third of the activating Ca$^2+$ comes through Na$^+$/Ca$^2+$
exchange and approximately two-thirds through L-type Ca$^2+$
channels. An alternative method of analysis, using the inward tail
current as a measure of the total sarcolemmal Ca$^2+$ flux from
which the Ni2+-sensitive Na$^+$/Ca$^2+$ exchange current
was subtracted to obtain the Ca$^2+$ influx through the channels,
suggests that L-type Ca$^2+$ channels and Na$^+$/Ca$^2+$
exchange are almost equally important in the activation of contraction.
Furthermore, the time course of cell shortening is not adequately
explained by sarcolemmal Ca$^2+$ influx through the channels
alone, but is well approximated by the sum of Ca$^2+$ influx
through the channels and the exchanger. The present results indicate
that reverse Na$^+$/Ca$^2+$ exchange in crucian carp ventricular
myocytes has sufficient capacity to trigger contraction and suggest
that the exchange current makes a significant contribution to contractile
Ca$^2+$ during the physiological action potential. The relative
significance of channels and exchanger molecules in sarcolemmal Ca$^2+$
entry into crucian carp ventricular myocytes was unaffected by thermal
acclimation when determined at 22 degrees C.
@article{Vorn_1999_1763,
abstract = {Influx of extracellular {C}a$^{2+}$ plays a major role in the activation
of contraction in fish cardiac cells. The relative contributions
of {N}a$^{+}$/{C}a$^{2+}$ exchange and L-type {C}a$^{2+}$ channels
to {C}a$^{2+}$ influx are, however, unknown. Using a physiological
action potential as the command pulse in voltage-clamped heart cells,
we examined sarcolemmal {C}a$^{2+}$ influx through {N}a$^{+}$/{C}a$^{2+}$
exchange and L-type {C}a$^{2+}$ channels in crucian carp (Carassius
carassius L.) ventricular myocytes. When other cation conductances
were blocked, a Ni2+-sensitive current with the characteristic voltage-
and time-dependent properties of the {N}a$^{+}$/{C}a$^{2+}$ exchange
current could be distinguished. At the maximum overshoot voltage
of the ventricular action potential (+40 mV; [{N}a$^{+}$]i=10 mmol
l-1), the density of the {N}a$^{+}$/{C}a$^{2+}$ exchange current
was 2.99+/-0.27 pA pF-1 for warm-acclimated fish (23 degrees C) and
2.38+/-0.42 pA pF-1 for cold-acclimated fish (4 degrees C) (means
+/- s.e.m., N=5-6; not significantly different, P=0.26). The relative
contributions of the {N}a$^{+}$/{C}a$^{2+}$ exchanger and L-type
{C}a$^{2+}$ channels to {C}a$^{2+}$ influx were estimated using two
partly different methods. Integration of the Ni2+-sensitive {N}a$^{+}$/{C}a$^{2+}$
exchange current and the verapamil- and Cd2+-sensitive L-type {C}a$^{2+}$
current suggests that, during the action potential, approximately
one-third of the activating {C}a$^{2+}$ comes through {N}a$^{+}$/{C}a$^{2+}$
exchange and approximately two-thirds through L-type {C}a$^{2+}$
channels. An alternative method of analysis, using the inward tail
current as a measure of the total sarcolemmal {C}a$^{2+}$ flux from
which the Ni2+-sensitive {N}a$^{+}$/{C}a$^{2+}$ exchange current
was subtracted to obtain the {C}a$^{2+}$ influx through the channels,
suggests that L-type {C}a$^{2+}$ channels and {N}a$^{+}$/{C}a$^{2+}$
exchange are almost equally important in the activation of contraction.
Furthermore, the time course of cell shortening is not adequately
explained by sarcolemmal {C}a$^{2+}$ influx through the channels
alone, but is well approximated by the sum of {C}a$^{2+}$ influx
through the channels and the exchanger. The present results indicate
that reverse {N}a$^{+}$/{C}a$^{2+}$ exchange in crucian carp ventricular
myocytes has sufficient capacity to trigger contraction and suggest
that the exchange current makes a significant contribution to contractile
{C}a$^{2+}$ during the physiological action potential. The relative
significance of channels and exchanger molecules in sarcolemmal {C}a$^{2+}$
entry into crucian carp ventricular myocytes was unaffected by thermal
acclimation when determined at 22 degrees C.},
added-at = {2009-06-03T11:20:58.000+0200},
author = {Vornanen, M},
biburl = {https://www.bibsonomy.org/bibtex/2121ef006793d9de1b09d1d6801ed7cd8/hake},
description = {The whole bibliography file I use.},
file = {Vorn_1999_1763.pdf:Vorn_1999_1763.pdf:PDF},
interhash = {8f50343fb2d0af582906bab83b884153},
intrahash = {121ef006793d9de1b09d1d6801ed7cd8},
journal = {J. Exp. Biol.},
key = 38,
keywords = {0010359679 ATPase, Acids, Acute Adaptation, Adenosine, Adolescent, Adult, Aged, Agents, Agonists, Animals, Anoxia, Anti-Bacterial Atrial Biopsy, Carbachol, Cardiotonic Cardiovascular Carps, Child, Chronic Contraction, Cyanide, Diagnosis, Differential, Disease, Distribution, Ear Ear, Electrophysiology, Europe, Fast-Twitch, Fatty Female, Fibers, Follow-Up Function, Gov't, Heart Hodgkin Humans, In Incidence, Lymphoma, Male, Media, Membranes, Middle Middle, Muscarine, Muscarinic Muscle Myocardial Needle, Neoplasms, Non-Hodgkin, Non-U.S. Otitis Outcome, Parvalbumins, Physiological, Preschool, Purines, Rate, Registries, Relaxation, Research Reticulum, Rhabdomyosarcoma, Sarcoplasmic Sex Sodium Studies, Support, Temperature, Treatment Ventricular Vitro, {C}a$^{2+}$-Transporting},
month = Jul,
pages = {1763-75},
timestamp = {2009-06-03T11:21:35.000+0200},
title = {{N}a$^{+}$/{C}a$^{2+}$ exchange current in ventricular myocytes of
fish heart: contribution to sarcolemmal {C}a$^{2+}$ influx},
url = {http://jeb.biologists.org/cgi/reprint/202/13/1763},
volume = {202 (Pt 13)},
year = 1999
}