Nonparallel Isometric Tension Response of Rabbit Soleus Skinned Muscle Fibers to Magnesium Adenosine Triphosphate and Magnesium Inosine Triphosphate

It has long been accepted that M g A T P is the energy source for contraction. Evidence has also accumulated indicating that M g A T P plays an important role in the regulation of contraction (Weber and Murray, 1973; Inoue and Tonomura , 1974; Godt, 1974; Orentlicher et al., 1977). In an a t tempt to better understand the dual role of ATP in contraction, several researchers have studied the effects on contraction of replacing ATP in contracting solutions with other nucleotides such as ITP, UTP , and G T P (Weber, 1969; Reuben et al., 1971). Two measures associated with muscle contraction have been used, hydrolysis of nucleotide by myosin and isometric tension development by skinned muscle fibers. An implied assumption in these nucleotide replacement studies is that the muscle will use and react to these nucleotides in an analogous fashion, and that differences in muscle response reflect quanti tat ive but not qualitative differences.-ia the rate processes governing muscle contraction. From the studies examining nucleotide hydrolysis by rabbit myofibrils and J. GEN. PHYSIOL. (~) The Rockefeller University Press 9 0022-1295/79/08/0261/14 $1.00 261 Volume 74 August 1979 261-274 on Jne 7, 2017 D ow nladed fom Published August 1, 1979