Abstract
The role of newly synthesized ATP in cyclic GMP-induced relaxation was studied in membrane-permeabilized longitudinal muscle preparations of the rat proximal colon . Cyclic GMP and 8-bromo cGMP induced concentration-dependent relaxation of α-toxin permeabilized preparations which were precontracted by 3μM Ca2+ in the presence of 4 mM ATP and 5 mM phosphocreatine (PC). The relaxation by 8-bromo cGMP was inhibited by Rp-8-pCPT-cGMPS, an inhibitor of cyclic GMP-dependent protein kinase . The relaxation was inhibited by removal of PC from the bathing solution, in spite of the presence of ATP. The relaxation was also inhibited by dinitrofluorobenzene (DNFB), a selective inhibitor of creatine kinase. The removal of PC or treatment with DNFB is known to produce accumulation of ADP within smooth muscle cell, however, ADPβS did not affect the relaxation.After irreversible inhibition of endogenous creatine kinase by DNFB in β-escin permeabilized preparations, treatment of the preparations with exogenous creatine kinase restored the relaxation. In the presence of ADP and PC but without ATP, 8-bromo cGMP induced the relaxation to the similar extent to that in the presence of ATP and PC . These results suggest that ATP newly synthesized from ADP and PC by creatine kinase is essential for cyclic GMP-induced relaxation of the smooth muscle preparations obtained from the proximal colon of rats.
