ARF-INDEPENDENT INHIBITION OF THE CARBACHOL-INDUCED CONTRACTIONS BY BREFELDIN-A IN INTESTINAL SMOOTH-MUSCLE

The aim of this study was to determine whether an ADP ribosylation fac tor (ARF)-regulated pathway is involved in the carbachol-induced contr action in rat intestinal smooth muscle. Brefeldin A, a known inhibitor of the guanine nucleotide exchange activity on ARF, reversibly inhibi ted the carbachol-induced contraction in intact ileal muscle strips, w hereas the carbachol-and guanosine 5'-O-(3-thiotriphosphate)-induced i ncreases in the Ca2+ sensitivity of myofilaments in beta-escin-permeab ilized strips were not affected. The high-K+-induced contraction in in tact strips was also inhibited by brefeldin A. In isolated ileal myocy tes, brefeldin A inhibited the Ca2+ channel current, indicating that t he inhibitory effect of brefeldin A in intact cells is related to an i nhibition of voltage-dependent Ca2+ channels. Furthermore, the loading of permeabilized strips with the combination of the recombinant fully myristoylated ARF1, the guanine nucleotide exchange factor ARNO, and guanosine 5'-triphosphate did not change the tone at constant pCa (6.4 5) and did not modify the carbachol- and guanosine 5'-O-(3-thiotriphos phate)-induced Ca2+ sensitization. Taken together, these findings sugg est that an ARF-dependent pathway is not involved in the carbachol-ind uced contraction.