Sarco(endo)plasmic reticulum Ca2+ ATPases (SERCA1 and -2) in human extraocular muscles.
OBJECTIVE
To investigate the composition of the fibers in human extraocular muscles (EOMs) with respect to the sarco(endo)plasmic reticulum Ca(2+)ATPases (SERCA)-1 and -2 and to investigate possible correlations between SERCA and myosin heavy chain (MyHC) composition.


METHODS
EOM samples were processed for immunocytochemistry with monoclonal antibodies specific against SERCA1 (fast isoform), SERCA2 (slow isoform), or different MyHCs. A total of 1571 fibers were analyzed. Microsomal EOM fractions were analyzed with SDS-PAGE and immunoblots.


RESULTS
The fast fibers, containing MyHCIIa, accounted for 79% of the fibers in the orbital layer (OL) and 74% in the global layer (GL). More than 99% of these fibers contained SERCA1, and 86% of them coexpressed SERCA1 and -2. Almost all slow fibers stained with SERCA2; 54% of those in the GL and all in the OL coexpressed SERCA1 and -2. Fifteen percent of the fibers in the GL and less than 1% in the OL were MyHCeom(pos)/MyHCIIa(neg) fibers. All these contained SERCA1 and in the OL also stained strongly with anti-SERCA2. Biochemically SERCA2 was more abundant than SERCA1.


CONCLUSIONS
The human EOMs had a very complex pattern of expression of the major protein regulating fiber relaxation rate. The coexistence of SERCA1 and -2, together with complex mixtures of MyHCs in most of the fibers provide the human EOMs with a unique molecular portfolio that allows a highly specific fine-tuning regimen of contraction and relaxation.
Kjellgren
Daniel
D
Department of Clinical Science, Section of Ophthalmology, University of Umeå, S-901 85 Umeå, Sweden.
Ryan
Michelle
M
Ohlendieck
Kay
K
Thornell
Lars-Eric
LE
Pedrosa-Domellöf
Fatima
F
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000911:Antibodies, Monoclonal; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007527:Isoenzymes; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000201:enzymology; D018995:Myosin Heavy Chains / Q000378:metabolism; D009801:Oculomotor Muscles / Q000201:enzymology*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases
D000911:Antibodies, Monoclonal; D007527:Isoenzymes; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D018995:Myosin Heavy Chains; C506943:ATP2A1 protein, human; C506946:ATP2A2 protein, human; D000252:Calcium-Transporting ATPases