Co-ordinated expression of contractile and non-contractile features of control equine muscle fibre types characterised by immunostaining of myosin heavy chains.
Combined methodologies of immunohistochemistry, histochemistry and photometric image analysis were applied: (1) to characterise control equine skeletal muscle fibres according to their myosin heavy chain (MyHC) composition and (2) to determine on a fibre-to-fibre basis the correlation between contractile [i.e. MyHC(s), myofibrillar ATPase (mATPase) and sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) isoforms], metabolic [i.e. succinate dehydrogenase (SDH) and alpha-glycerophosphate dehydrogenase (GPD) activities, glycogen and phospholamban (PLB) contents], and morphological [i.e. cross-sectional area (CSA), capillary and nuclear densities] features of individual myofibres. An accurate delineation of MyHC-based fibre types was obtained with the immunohistochemical method developed. This protocol showed a high sensitivity and objectivity to delineate hybrid fibres with overwhelming dominance of one MyHC isoform and, furthermore, it allowed a semiquantitative delineation of fast hybrid fibres according to the predominant MyHC isoform expressed. The phenotypic differences in contractile, metabolic and morphological properties seen between fibre types were related to MyHC content. Slow fibres had the lowest mATPase activity (related to shortening velocity), the highest SDH activity (oxidative capacity), the lowest GPD activity (glycolytic metabolism) and glycogen content, the smallest CSA, the greatest capillary and nuclear densities, and expressed slow SERCA isoform and PLB, but not the fast SERCA isoform. The reverse pattern was true for pure IID/X fibres, and type IIA fibres had intermediate properties. Hybrid IIAD/X fibres had mean values intermediate to those of their respective pure phenotypes. Discrimination of fibres according to their MyHC content was possible on the basis of their contractile and non-contractile profiles. These intrafibre interdependencies suggest that, even when controlled by different mechanisms, myofibres of control horses exhibit a high degree of co-ordination in their physiological, biochemical and anatomical features.
Quiroz-Rothe
E
E
Department of Comparative and Pathological Anatomy (Muscle Biology Laboratory), University of Cordoba, Campus de Rabanales, Edificio de Sanidad Animal, Crtra. Madrid-Cadiz, km 396, 14014 Cordoba, Spain.
Rivero
J L
JL
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D002135:Calcium-Binding Proteins / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002196:Capillaries / Q000502:physiology; D002467:Cell Nucleus / Q000502:physiology; D005260:Female; D005993:Glycerolphosphate Dehydrogenase / Q000378:metabolism; D006736:Horses; D007150:Immunohistochemistry; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000737:chemistry* / Q000502:physiology; D009210:Myofibrils / Q000201:enzymology; D018995:Myosin Heavy Chains / Q000032:analysis*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D013385:Succinate Dehydrogenase / Q000378:metabolism; D000099211:Phospholamban
D000251:Adenosine Triphosphatases; D002135:Calcium-Binding Proteins; D000252:Calcium-Transporting ATPases; D005993:Glycerolphosphate Dehydrogenase; D018995:Myosin Heavy Chains; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D013385:Succinate Dehydrogenase; D000099211:Phospholamban