R. Viannajorge et al., FUNCTIONAL-EFFECTS OF URIDINE TRIPHOSPHATE ON HUMAN SKINNED SKELETAL-MUSCLE FIBERS, Canadian journal of physiology and pharmacology, 76(2), 1998, pp. 110-117
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). To
tal 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 Ca2+-activated tension, both effects being large
r in slow-than in fast-type fibers (ii) markedly reduced Ca2+ uptake b
y the SR (evaluated by the caffeine-evoked tension) in both fiber type
s; (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 substitu
te for ATP as a substrate for the Ca ATPase pump and as an agonist of
the ryanodine-sensitive Ca2+-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 pre
sent data reveal important differences between the effects of UTP on h
uman versus rat muscle fibers.