Ca2+ sensitivity of stunned myocardium after skinning using retrograde infusion of detergent

Myofilament Ca2+ desensitization contributes to the contractile dysfunction of ischemic/reperfused ("stunned") myocardium. We examined the presence of reduced Ca2+ sensitivity of isometric force in chemically skinned Fibers o btained from stunned myocardium using different modes of applying the deter gent Triton X-100. Langendorff-perfused rat hearts underwent 20 min ischemi a/20 min reperfusion, which caused a 35+/-3% decrease in left ventricular d eveloped pressure, compared to continuously perfused control hearts. Stunne d and control hearts: were randomly allocated to two different permeabiliza tion protocols: In group A, trabeculae were dissected and immersed in skinn ing solution containing 1% Triton X-100 for 20 min. Group B hearts remained fixed to the aortic cannula and skinning solution was infused retrogradely for 6 min prior to dissection of trabeculae. Extraction of cytosolic marke r proteins was more complete in group-B than in group-A preparations. Group -A preparations from stunned hearts exhibited significant Ca2+ desensitizat ion (pCa(50) = 5.07 and 5.15 in stunned and control myocardium, respectivel y). In group B no such difference was observed, all preparations showing hi gher Ca2+ sensitivity and maximum Force than group-a preparations (pCa(50) = 5.32 in stunned versus 5.33 in control hearts). Prolonging group-A skinni ng to 150 min also abolished the difference in Ca2+ sensitivity between stu nned and control myocardium. In conclusion, compared to a conventional prot ocol, skinning by perfusion results in more complete permeabilization and b et-ter preservation of myocardial contractile function. Ischemia/reperfusio n at this moderate degree of contractile dysfunction induces Ca2+ desensiti zation at least partially by factors that can be extracted by thorough skin ning.