Vianna-Jorge R, Oliveira C F, Mounier Y, Suarez-Kurtz G
Departamento de Farmacologia, Universidade Federal do Rio de Janeiro, Brazil.
Can J Physiol Pharmacol. 1998 Feb;76(2):110-7.
Chemically skinned human skeletal muscle fibers were used to study the effects of uridine triphosphate (UTP) on the tension-pCa relationship and on Ca2+ uptake and release by the sarcoplasmic reticulum (SR). Total replacement (2.5 mM) of adenosine triphosphate (ATP) with UTP (i) displaced the tension-pCa relationship to the left along the abcissae and increased maximum Ca(2+)-activated tension, both effects being larger in slow- than in fast-type fibers; (ii) markedly reduced Ca2+ uptake by the SR (evaluated by the caffeine-evoked tension) in both fiber types; (iii) had no effect on the rate of depletion of caffeine-sensitive Ca2+ stores during soaking in relaxing solutions; (iv) induced tension in slow- but not in fast-type fibers. The effects on the SR functional properties are consistent with the notion that UTP is a poor substitute for ATP as a substrate for the Ca ATPase pump and as an agonist of the ryanodine-sensitive Ca(2+)-release channel. The UTP-induced tension in human slow-type fibers is attributed to effect(s) of the nucleotide on the tension-pCa relationship of the contractile machinery. The present data reveal important differences between the effects of UTP on human versus rat muscle fibers.
采用化学去膜的人骨骼肌纤维来研究三磷酸尿苷（UTP）对张力-pCa关系以及对肌浆网（SR）摄取和释放Ca2+的影响。用UTP完全替代（2.5 mM）三磷酸腺苷（ATP）：（i）使张力-pCa关系沿横坐标向左移位，并增加最大Ca2+激活张力，这两种效应在慢肌纤维中比在快肌纤维中更大；（ii）在两种纤维类型中均显著降低SR对Ca2+的摄取（通过咖啡因诱发的张力评估）；（iii）在浸泡于松弛溶液期间，对咖啡因敏感的Ca2+储存耗尽速率没有影响；（iv）在慢肌纤维中诱导产生张力，但在快肌纤维中则不然。对SR功能特性的影响与以下观点一致，即UTP作为Ca ATP酶泵的底物以及作为兰尼碱敏感的Ca2+释放通道的激动剂，是ATP的较差替代物。UTP在人慢肌纤维中诱导产生的张力归因于该核苷酸对收缩机制的张力-pCa关系的影响。目前的数据揭示了UTP对人肌纤维和大鼠肌纤维的影响之间的重要差异。
