Frisk, Michael

Louch, William E.

Sejersted, Ole M.

Elsevier - Publisher Connector 

Sunday, February 26, 2012 139a694-Pos Board B480
Variable T-Tubule Density and Organization in Rat Atrial
Cardiomyocytes
Michael Frisk1,2, Ole M. Sejersted1,2, William E. Louch1,2.
1Center for Heart Failure Research, University of Oslo, Oslo, Norway,
2Institute for Experimental Medical Research, Oslo University Hospital,
Ulleva˚l, Oslo, Norway.
T-tubules are invaginations in the cellular membrane of the myocyte. In ven-
tricular cardiomyocytes initiation of excitation-contraction coupling is highly
localized near the t-tubules, which span the cell in a predominantly transverse
orientation. While t-tubules have traditionally been thought to be virtually ab-
sent from atrial cells, recent data indicate that a fairly substantial network is
present in the atria of large mammals. We presently compared the t-tubule net-
work of atrial and ventricular cardiomyocytes in 6 week-old Wistar rats. Atrial
myocytes were isolated by dicing and agitating tissue in the presence of colla-
genase, and ventricular cells were isolated by Langendorf perfusion. Cell mem-
brane and t-tubules were stained with di-8-ANEPPS and imaged by confocal
microscopy. 100% of ventricular and 37% of atrial cardiomyocytes possessed
a measurable t-tubular density (defined as occupying >5% of the cytosolic
lumen). In the tubulated atrial cells, t-tubular density was similar to that ob-
served in ventricular myocytes (% cross-sectional area = 16% in atrial vs.
17% in ventricular cardiomyocytes, P=0.76). Surprisingly, 10% of atrial myo-
cytes exhibited an organized, largely transverse structure. Power spectral anal-
ysis revealed that this organization was somewhat less homogeneous than that
observed in ventricular cells, as atrial myocytes exhibited a higher proportion
of longitudinal elements (ratio of peak power to between-peak power = 3.15
in atrial vs. 5.13 in ventricular cells, P=0.02). Neither density nor organization
of t-tubules was correlated to atrial cardiomyocyte size. Thus, in contrast to
several previous reports, a significant proportion of rat atrial cardiomyocytes
possess a t-tubule network which is as extensive as that observed in ventricular
cells. Furthermore, in a minority of atrial cardiomyocytes (approximately 10%)
the t-tubular network is well organized into a predominately transverse
structure.
695-Pos Board B481
Altered Action Potential Heterogeneity in Hypertrophic Right Ventricles
of Rats
Matthew E.L. Hardy1, Olivier Bernus2, Ed White1.
1University of Leeds, Leeds, United Kingdom, 2Inserm U-1045, Universite
de Bordeaux, Bordeaux, France.
Hypertrophy of the myocardium causes electrophysiological remodeling and
changes in action potential duration (APD). The right ventricle (RV) becomes
hypertrophied and fails under conditions of pulmonary artery hypertension
(PAH). The current study evaluated changes in APD heterogeneity in a rodent
model of PAH.
Male Wistar rats were given a single i.p. injection of monocrotaline (60 mg/kg)
or an equivalent volume of saline. When clinical symptoms of heart failure
became apparent (3-4 weeks later) animals were euthanized and the hearts ex-
cised. Electrical activity was optically monitored from the epicardial surface of
both ventricles in intact hearts using di-4-ANEPPS. The myocardium was stim-
ulated at basic cycle lengths (BCLs) between 80-160 ms. APD at 80% repolar-
ization (APD80) was calculated at the mid-LV, mid-RV and right ventricular
outflow tract (RVOT) regions.
At 160 ms BCL, APD80 was significantly longer in hypertrophied compared to
sham in both RV regions however 8/9 hypertrophied hearts had a longer APD80
in the RVOT vs. mid-RV, whilst in 11/11 sham hearts the APD80 was shorter in
the RVOT. The changes in APD between the two RV regions were significantly
different (MCT RVOT - mid-RV þ6.6 5 2.6 ms vs. Sham RVOT - mid-RV
6.8 5 1.3 ms, p<0.0001 unpaired Student’s t-test). APD restitution curves
were significantly steeper in the mid-RV and RVOT of hypertrophied hearts
than the mid-LV or mid-LV, mid-RV and RVOT of sham hearts.
These data show that electrical remodeling in monocrotaline treated RV was
heterogenous. These regionally dependant changes in APD may contribute to
the pro-arrhythmic state of hypertensive and hypertrophic RVs.
Supported by the MRC.
696-Pos Board B482
Conditional SERCA2 Ablation Impairs Systolic and Diastolic Perfor-
mance of Isolated Perfused Hearts
Frazer I. Heinis1, Kristin B. Andersson2, Geir Christensen2,
Joseph M. Metzger1.
1University of Minnesota, Minneapolis, MN, USA, 2University of Oslo,
Oslo, Norway.
Highly orchestrated contraction and relaxation of the myocardium depends
on rapid release and reuptake of Ca2þ from the sarcoplasmic reticulum (SR).SERCA2a, a cardiac SR Ca2þ-ATPase, is a major contributor to re-
sequestration of Ca2þ and shows reduced expression with age and in heart fail-
ure. Conditional deletion of the Serca2 gene from the hearts of fl/fl mice results
in progressive diastolic dysfunction, heart failure, and death over a period of
two months. To gain insight into the interplay between Ca2þ-mishandling
and the evolution of cardiac pump failure we studied mice at 1 and 4 weeks fol-
lowing cardiac specific cre-mediated deletion of the Serca2 gene from fl/fl
mice. At each time point, isolated hearts were subjected to paced stimulation
across a broad frequency range, followed by ischemia/reperfusion injury. At
both 1 and 4 weeks, SERCA2a loss resulted in profound contractile deficits
and diastolic impairment relative to normal hearts. However, there was no
difference in the relative performance of normal and KO hearts following
ischemia/reperfusion injury, suggesting that depleting SR Ca2þ is not protec-
tive from ischemia. Curiously, 1 week after Serca2 deletion, when 15-20%
of baseline SERCA2a protein remains, diastolic performance in response to
stepped increases in pacing frequency was impaired to a similar degree as in
4-week KO hearts containing <5% original protein levels. We are further in-
vestigating the consequences of SERCA2a loss shortly after gene deletion, at
times less than one week after knockout, to construct a detailed dose-
response relationship between titrated changes in SR Ca2þ handling and con-
tractile function.
697-Pos Board B483
Elevated Plasma Oxidized Lipids in Severe Pulmonary Hypertension are
Fully Restored by Estrogen Therapy
Soban Umar, Mansour Eghbali, Katharina Volz, Denise Mai,
Mansoureh Eghbali.
Univ of California, Los Angeles, Los Angeles, CA, USA.
Recently we reported that estrogen (E2) rescues pre-existing severe pulmonary
hypertension (PH). PH is associated with pulmonary vascular remodelling.
Vascular disorders result from complex interactions between oxidized-
lipoproteins, monocytes/macrophages, injured endothelium and smooth muscle
cells. Biological oxidation products of arachidonic acid, including prostaglan-
dins (PGs), thromboxanes (TXs), hydroxyeicosatetraenoic acids (HETEs) and
hydroxyoctadecadienoic acids (HODEs) play an important role in the patho-
genesis of atherosclerosis, yet their role in PH is not fully known. Here we
investigated whether PH is associated with increased plasma levels of
oxidized-lipids, and if E2 can restore their levels. To induce PH, rats received
monocrotaline (MCT, 60mg/kg, s.c.). Severe PH was established 21-days after
MCT (PH, n=8). E2 (42.5ug/kg/day, s.c., n=6) was given from day-21 to 30.
Saline treated rats served as control (CTRL, n=7). Cardiac catheterization was
performed terminally to record RV-pressure (RVP). Plasma HODEs, HETEs,
TXs and PGs were determined by mass-spectrometry. p<0.05 was considered
significant. Values were mean5SE. Rats developed severe PH [RVP=6852
vs. 3152 mmHg in CTRL, p<0.01). E2 rescued PH (RVP=3851 mmHg,
p<0.01 vs. PH). PH was associated with increased plasma levels (ng/ml of
plasma) of 9-HODE (22175381 vs. 9495255 in CTRL, p<0.05) and
13-HODE (43475439 vs. 18715609 in CTRL, p<0.05). E2 reversed PH-
induced increase in HODEs (9-HODE=9765259; 13-HODE=24695531; all
p<0.05 vs. PH). PH led to significantly elevated plasma 5-HETE (938577 vs.
663515), 12-HETE (97205972 vs. 66335522) and 15-HETE (818562 vs.
53457; all p<0.05 vs. CTRL). E2 fully reversed the increase in HETEs
(5-HETE=708537; 12-HETE=69815248; 15-HETE=622550; p<0.05 vs.
PH). PH also led to elevated plasma TXB2 (3.550.2 vs. 2.850.1), PGD2
(98511 vs. 3557) and PGE2 (2751 vs. 1352; all p<0.05 vs. CTRL) and
E2 restored their levels (TXB2=2.650.2; PGD2=54510; PGE2=1952; all
p<0.05). In conclusion, severe PH is associated with increased plasma levels
of oxidized lipids that are fully restored by E2.
698-Pos Board B484
Structural and Hemodynamic Changes Associated with Physiologic Heart
Hypertrophy of Pregnancy are Reversed Postpartum
Soban Umar, Andrea Iorga, Rangarajan D. Nadadur, Marjan Amjedi,
Mansour Eghbali, Ray Chui, Humann Matori, Mansoureh Eghbali.
Univ of California, Los Angeles, Los Angeles, CA, USA.
We have previously characterized pregnancy-induced physiological heart
hypertrophy. Pregnancy is associated with ventricular hypertrophy and short-
term systolic and diastolic dysfunction due to volume-overload. Here we inves-
tigated whether cardiac structural and hemodynamic changes associated
with pregnancy are reversed postpartum. Female mice (3-4month, C57BL/6)
were used in non-pregnant diestrus-stage (NP), late pregnant (LP), 1-day
postpartum (PP1), or 7-days PP (PP7). Echocardiography and cardiac-
catheterisation were performed to monitor cardiac-hemodynamics. RT-PCR
was performed to determine vascular endothelial growth factor (VEGF) and
matrix metalloproteinase-2 (MMP2) transcripts. Trichrome staining for cardiac


Variable T-Tubule Density and Organization in Rat Atrial Cardiomyocytes 

file:///data/remote/core/dit/data/elsevier/pdf/9a4/aHR0cDovL2FwaS5lbHNldmllci5jb20vY29udGVudC9hcnRpY2xlL3BpaS9zMDAwNjM0OTUxMTAyMTE0eA==.pdf

Variable T-Tubule Density and Organization in Rat Atrial Cardiomyocytes

Abstract

Similar works

Full text

Available Versions

Elsevier - Publisher Connector

Elsevier - Publisher Connector