Essential role of newly synthesized ATP for cyclic GMP-induced relaxation in alpha-toxin permeabilized smooth muscle of rat proximal colon.

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 alpha-toxin permeabilized preparations which were precontracted by 3 microM 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, ADPbetaS did not affect the relaxation. After irreversible inhibition of endogenous creatine kinase by DNFB in beta-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.