title: Effects of uridine triphosphate on skinned skeletal muscle fibers of the rat.
abstract: Chemically skinned muscle fibers from rat extensor digitorum longus muscle were used to study the effects of uridine triphosphate (UTP) on Ca2+ uptake and release by the sarcoplasmic reticulum (SR) and on Ca2+-activated tensions. Total replacement (2.5 mM) of adenosine triphosphate (ATP) with UTP (i) increased submaximal Ca2+-induced tension (pCa 6.2-5.8) but diminished Po, the maximum tension elicited by pCa 4.2, by ca. 15%, (ii) markedly reduced Ca2+ uptake by the SR (evaluated by caffeine-elicited tension); and (iii) induced tension in Ca2+-loaded fibers. The UTP-induced tension averaged 55% of Po and its rates of development and decay were considerably slower than those of caffeine-evoked tension. The UTP-induced tension (i) depended on the Ca2+-loading conditions; (ii) was reversibly blocked by brief (15 s) exposures of Ca2+-loaded fibers to 5 mM EGTA or by pretreatment with caffeine; (iii) was abolished by functional disruption of the SR with the nonionic detergent Brij-58; and (iv) persisted after blockade of the SR Ca2+ release channels with ruthenium red. Exposure of Ca2+-loaded fibers to UTP depressed the tension elicited subsequently by caffeine, and enhanced the rate of depletion of caffeine-sensitive Ca2+ stores during soaking in relaxing solutions containing 5 mM EGTA. The UTP-induced tension is attributed to increased release of Ca2+ from the SR, via a ruthenium red insensitive pathway(s), combined with reduced Ca2+ uptake by the SR and increased Ca2+ affinity of the contractile proteins.
authors: Departamento de Bioquimica Medica, Instituto de Ciencias Biomedicas, ICB-CCS, Universidade Federal do Rio de Janeiro, Cidade Universitaria, Rio de Janeiro, Brazil.
authors: G
authors: G
authors: Suarez-Kurtz
authors: M P
authors: MP
authors: Catinot
authors: C G
authors: CG
authors: Ponte
authors: R
authors: R
authors: Vianna-Jorge
authors: Y
authors: Y
authors: Mounier
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000493:pharmacokinetics*; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D004396:Coloring Agents; D004347:Drug Interactions; D018485:Muscle Fibers, Skeletal / Q000187:drug effects*; D051381:Rats; D012430:Ruthenium Red / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D014544:Uridine Triphosphate / Q000494:pharmacology*
chemical_list: D000697:Central Nervous System Stimulants; D004396:Coloring Agents; D012430:Ruthenium Red; D002110:Caffeine; D000255:Adenosine Triphosphate; D002118:Calcium; D014544:Uridine Triphosphate