Functional studies in human cardiac tissue obtained from endomyocardial biopsies

IntrodictioB: Tissue obtained from endomyocardial biopsies in recipients of heart transplants is used to determine histopathologkal characteristics in immunosuppressed patients. Functional studies are performed only when larger amounts of cardiac tissue are available. We address the possibility of using cardiac tissue from biopsies to appraise functional activity in vitro in response to different treatments Methods: Endomyocardial samples (n - 4) from adult heart transplanted patients under UIC Heart Transplant protocol were obtained with an 8F Caves-Shultz (Stanford) bioptome and placed into a cold high relaxing (HR) solution containing 10 mM EGTA, 2 mM Mg;. 5 mM MgATP. 12 mM creatine phosphate and 20 mM MOPS (ionic strength 150 mM, pH = 7.0) with 10 mM 2,3,-butanedione monoxamine (BDM) and 1:1 glycerol. The biopsied tissue was dissected into fiber bundles with 100-200 urn in diameter and 4-6 mm in length and attached at one end to a metal post connected to a micromanipulator and at the other end to a force transducer whose output was determined on a chart recorder. The fibers were skinned in HR detergent solution containing 1% Triton X-100 and then immersed in solutions containing increasing Ci'concentration with pCa values between 4.5 and 8 (pCa = -log [Or]). Individual pCa-force determinations were normalized to a maximum force developed by each fiber. The GraphPad Prism software was used for curve fitting. Resatts: The Ca²⁺ concentration at which the fibers develop 50J. of maximal force (pCa2 ) 3 10 was 5.88 ± 0.02, while the myofibrilar £F cooperativity during the force development, g so measured as the Hill coefficient, was 1.87 + 0.17. 5 Coaduioos: These preliminary results show that samples obtained from biopsied human < tissue can be successfully used for functional studies. pea Further investigations with biopsied material provide a means to study the effect of specific drugs directly on human cardiac myofilaments.