Effects of adenovirus-mediated sorcin overexpression on excitation-contraction coupling in isolated rabbit cardiomyocytes.
To evaluate the effect of sorcin on cardiac excitation-contraction coupling, adult rabbit ventricular myocytes were transfected with a recombinant adenovirus coding for human sorcin (Ad-sorcin). A beta-galactosidase adenovirus (Ad-LacZ) was used as a control. Fractional shortening in response to 1-Hz field stimulation (at 37 degrees C) was significantly reduced in Ad-sorcin-transfected myocytes compared with control myocytes (2.10+/-0.05% [n=311] versus 2.42+/-0.06% [n=312], respectively; P<0.001). Action potential duration (at 20 degrees C) was significantly less in the Ad-sorcin group (458+/-22 ms, n=11) compared with the control group (520+/-19 ms, n=10; P<0.05). In voltage-clamped, fura 2-loaded myocytes (20 degrees C), a reduced peak-systolic and end-diastolic [Ca2+]i was observed after Ad-sorcin transfection. L-type Ca2+ current amplitude and time course were unaffected. Caffeine-induced Ca2+ release from the sarcoplasmic reticulum (SR) and the accompanying inward Na+-Ca2+ exchanger (NCX) current revealed a significantly lower SR Ca2+ content and faster Ca2+-extrusion kinetics in Ad-sorcin-transfected cells. Higher NCX activity after Ad-sorcin transfection was confirmed by measuring the NCX current-voltage relationship. beta-Escin-permeabilized rabbit cardiomyocytes were used to study the effects of sorcin overexpression on Ca2+ sparks imaged with fluo 3 at 145 to 160 nmol/L [Ca2+] using a confocal microscope. Under these conditions, caffeine-mediated SR Ca2+ release was not different between the two groups. Spontaneous spark frequency, duration, width, and amplitude were lower in sorcin-overexpressing myocytes. In summary, sorcin overexpression in rabbit cardiomyocytes decreased Ca2+-transient amplitude predominantly by lowering SR Ca2+ content via increased NCX activity. The effect of sorcin overexpression on Ca2+ sparks indicates an effect on the ryanodine receptor that may also influence excitation-contraction coupling.
Seidler
Tim
T
Department of Cardiology and Pneumology, Georg-August-University Goettingen, Goettingen, Germany.
Miller
Stewart L W
SL
Loughrey
Christopher M
CM
Kania
Astrid
A
Burow
Annika
A
Kettlewell
Sarah
S
Teucher
Nils
N
Wagner
Stefan
S
Kögler
Harald
H
Meyers
Marian B
MB
Hasenfuss
Gerd
G
Smith
Godfrey L
GL
D000256:Adenoviridae / Q000235:genetics*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002135:Calcium-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D002478:Cells, Cultured; D004928:Escin / Q000494:pharmacology; D015870:Gene Expression; D018014:Gene Transfer Techniques; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism; D009200:Myocardial Contraction / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009532:Nickel / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010539:Permeability / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D012508:Sarcolemma / Q000187:drug effects / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism
D002135:Calcium-Binding Proteins; D012333:RNA, Messenger; C503113:SRI protein, human; D002110:Caffeine; D004928:Escin; D009532:Nickel; D002118:Calcium