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ENERGY DAN CARDIAC CONTRACTION dr. HUSNIL KADRI , M.Kes Biochemistry Departement Medical Faculty Of Andalas University Padang 3 TYPES OF MUSCLE TISSUE Skeletal muscle attaches to bone, skin or fascia striated with light & dark bands visible voluntary control of contraction & relaxation Extracell fluid calsium not important for contraction 2 3 TYPES OF MUSCLE TISSUE Cardiac muscle striated in appearance involuntary control autorhythmic because of built in pacemaker Extracell fluid calsium important for contraction External control of cardiac muscle is involuntary, via hormones and by the autonomic nervous system 3 3 TYPES OF MUSCLE TISSUE Smooth muscle attached to hair follicles in skin in walls of hollow organs -- blood vessels & GI nonstriated in appearance Involuntary Extracell fluid calsium important for contraction Control of smooth muscle is involuntary, via paracrine control, hormones, and the autonomic nervous system 4 MUSCLE FIBER OR MYOFIBERS Muscle cells are long, cylindrical & multinucleated Sarcolemma = muscle cell membrane Sarcoplasm filled with tiny threads called myofibrils & myoglobin (red-colored, oxygen-binding protein) CARDIAC MUSCLE CARDIAC MUSCLE TISSUE CARDIAC MUSCLE 20-8 CARDIAC MUSCLE branching cells containing 1-2 centrally located nuclei Contains actin and myosin myofilaments Intercalated disks: Specialized cell-cell contacts Desmosomes hold cells together and gap junctions allow action potentials Electrically, cardiac muscle behaves as single unit 20-9 Elongated, GAP JUNCTIONS low resistance connections small pores in the center of each gap junction allows ions and small peptides to flow from one cell to another action potential is propagated to adjacent muscle cells Heart behaves as a single motor unit THEORETICALLY, AN ION INSIDE AN SA NODAL CELL COULD TRAVEL THROUGHOUT THE HEART VIA THE GAP JUNCTIONS Sperelakis N, Kurachi Y, Terzic A, Cohen MV. Heart Physiology and Pathophysiology Academic Press, 2001 MITOCHONDRIA generate the energy in the form of adenosine triphosphate (ATP) maintain the heart’s contractile function and the associated ion gradients TRANSVERSE TUBULES T (transverse) tubules are invaginations of the sarcolemma into the center of the cell filled with extracellular fluid carry muscle action potentials down into cell Mitochondria lie in rows throughout the cell near the muscle proteins that use ATP during contraction MYOFIBRILS & MYOFILAMENTS Muscle fibers are filled with threads called myofibrils separated by SR (sarcoplasmic reticulum) Myofilaments (thick & thin filaments) are the contractile proteins of muscle SARCOPLASMIC RETICULUM (SR) System of tubular sacs similar to smooth ER in nonmuscle cells Stores Ca+2 in a relaxed muscle Release of Ca+2 triggers muscle contraction INTERNAL STRUCTURE OF A MUSCLE FIBER Muscle fibers are full of myofibrils, but also contain a number of notable chemicals and structures: sarcolemma = plasma membane transverse tubules = tunnel-like extensions of the sacrolemma sarcoplasm = cytoplasm sarcoplasmic reticulum (SR) = a network of membranous sacs around the myofibrils. The SR stores calcium ions. THICK & THIN MYOFILAMENTS THE SARCOMERE IS THE FUNCTIONAL SUBUNIT OF MUSCLE Electron micrographs of muscle fibers reveal that the striations are formed of alternating light [band I] and dark [band H] bands A sarcomere is defined as the part of a myofibril between two Z discs. As muscles contract, the Z discs move closer together, indicating that the sarcomeres themselves shorten THE PROTEINS OF MUSCLE Myofibrils are built of 3 kinds of protein: contractile proteins myosin and actin regulatory proteins which turn contraction on & off troponin and tropomyosin structural proteins which provide proper alignment, elasticity and extensibility titin, myomesin, nebulin and dystrophin MYOSIN Many different types Myosin V vesicle transport Myosin II skeletal and cardiac muscle contraction ACTIN FILAMENTS: Polymer of G-actin (43 kDa globular protein) In most cells, found at the periphery, underlying the cell surface ‘thin filaments’ in muscle Also in microvilli Also involved in cell shape changes SLIDING FILAMENT MECHANISM When muscles contract, thick and thin filaments move relative to each other As the Z discs move closer together, the sarcomere shortens Contraction is stimulated by calcium ions SLIDING FILAMENT MECHANISM CARDIAC MUSCLE: TWO CA2+ SOURCES CARDIAC VERSUS SKELETAL MUSCLE More sarcoplasm and mitochondria Larger transverse tubules located at Z discs, rather than at A-l band junctions Less well-developed SR Limited intracellular Ca+2 reserves more Ca+2 enters cell from extracellular fluid during contraction Prolonged delivery of Ca+2 to sarcoplasm, produces a contraction that last 10 -15 times longer than in skeletal muscle PHYSIOLOGY OF CARDIAC MUSCLE Autorhythmic cells contract without stimulation Contracts 75 times per min & needs lots O2 Larger mitochondria generate ATP aerobically Sustained contraction possible due to slow Ca+2 delivery Ca+2 channels to the extracellular fluid stay open EXCITATION-CONTRACTION COUPLING A muscle action potential stimulates release of Ca2+ ions from the SR Ca2+ ions bind to troponin, which causes tropomyosin to move off of the myosin-binding sites on actin The exposed binding sites bind to myosin, and contraction begins EXCITATION-CONTRACTION COUPLING CONTRACTION AND RELAXATION OF SKELETAL MUSCLE Key: = Ca2+ 1 Myosin heads hydrolyze ATP and become reoriented and energized ADP P ATP Contraction cycle continues if ATP is available and Ca2+ level in the sarcoplasm is high ATP ADP Copyright 2010, John Wiley & Sons, Inc. P 2 Myosin heads bind to actin, forming crossbridges ADP 4 As myosin heads bind ATP, the crossbridges detach from actin Copyright 2010, John Wiley & Sons, Inc. 3 Myosin crossbridges rotate toward center of the sarcomere (power stroke) MUSCLE METABOLISM: ENERGY FOR CONTRACTION Muscle cells need to generate large amounts of available energy during contractions Muscle cells have three ways to produce ATP: Aerobic cellular respiration Anaerobic cellular respiration Creatine phosphate CARDIAC MUSCLE METABOLISM: AEROBIC CELLULAR RESPIRATION PERAN RANTAI RESPIRASI asam lemak + gliserol b-oksidasi ATP 34 O2 glukosa Asetil KoA SAS 2H H2O rantai respirasi ADP Asam amino mitokondria RANTAI RESPIRASI 35 Penyedia sebagian besar energi untuk metabolisme melalui fosforilasi oksidatif. Komponen rantai respirasi tersusun dari potensial redok lebih negatif ke komponen dengan potensial redoks yg lebih positif. Jalur ini mengumpulkan & mengoksidasi sejumlah ekuivalen pereduksi (-H atau e) yang dihasilkan dari oksidasi karbohidrat, asam lemak, & protein. 36 PRODUK ATP PADA FOSFORILASI OKSIDATIF 37 Diperkirakan satu ATP disintesis setiap dua proton melewati tonjolan tsb. Hasilnya ialah; - 3 mol. ATP utk oksidasi 1 mol. NADH - 2 mol. ATP utk oksidasi 1 mol. FADH2 Laju fosforilasi oksidatif dikendalikan oleh; NADH, oksigen, ADP MUSCLE METABOLISM: CREATINE PHOSPHATE Creatine phosphate serves as an energy reservoir for muscle cells: Resting muscle cells store excess energy in creatine phosphate During exercise cells can quickly replenish their ATP supply using creatine-phosphate This supply of energy is only large enough for short bursts of activity (about 15 seconds) MUSCLE METABOLISM: ANAEROBIC METABOLISM For short time periods muscle cells can make ATP by glycolysis alone The pyruvate is converted into lactic acid and enters the blood if there is no oksigen (anaerobic) This source of ATP can only power muscle cells for about 30-40 seconds RESOURCES Akar AR. Cardiac Physiology (IV). Ankara University School of Medicine. Desember 2003. download 2011 Jenkins, Kemnitz, Tortora. Chapter 10 Muscle Tissue. Anatomy and Physiology. John Wiley & Son, inc. download 2011 Cardiovascular System: Heart. download 2011 Chapter 6 Histology. download 2011 Structure and Function of Skeletal Muscle. download 2011 Khan R. Year I Tutorial: Musculoskeletal System. download 2011. Murray RK. Muscle & the cytoskeleton. In:Harper’s Illustrated Biochemistry. 27th ed. pp 565-587