Involvement of protein kinase C in the relaxation ot acetylchoiine-shortened isolated intact smooth muscle cells from the guinea-Pig stomach

• Published in: Japanese Journal of Pharmacology 1995, Vol.67 (suppl.1), p.206-206
• Main Authors: Sanae Nakamura, Tsuyoshi Ishibashi, Mitsuo Mita, Takao Hashimoto, Kazuhiko Oishi, Masaatsu K.Uchida
• Format: Article
• Language: Japanese
• ISSN: 0021-5198

We have shown that the activation of protein kinase C (PKC) in the process of acetylcholine (ACh)-induced cell shortenin is necess for the subsequent relaxation of the shortene cells in the preparation of streptolysin-O-permeabilized smooth muscle cells (Jpn.J.Pharmacol.64,268P,1994). In order to clarify whether this PKC-dependent mechanism is physiologrcally important for the reiaxation of smooth muscles, we first investi ated the effect of a protein kinase C inhibitor, K-252b, on the relaxation of ACh-shortened isolated intact smooth muscle cells from the guinea-pig stomach. The isolated cells were placed on a sificon-coated glass slide, and cell shortenin was observed under phase-contrast microscopy. The cells shortened in response to ACh (10 μM) were readily extended by washing for 20 min. When the cell shortening was induced by AC in the presence of 10 μM K-252b, the extension of the shortened cells was almost completely blocked. These results indicate that the PKC-dependent relaxation mechanism is also involved in the relaxation of intact cells shortened in response to ACh. Next, the effect of K-252b on the relaxation of ACh-contracted whole smooth muscle tissues from the guinea-pig stomach was examined. Contractile response was recorded isotonically with a load of 0.5 g. In thrs case, the contracted tissues in response to ACh (10 μM) were readily relaxed by washing even if the contraction was induced by ACh in the presence of 3 μM K-252b. These results arise the possibility that the PKC-dependent relaxation mechanism, which actively participates in the relaxation of agonist-shortened individuai smooth muscle cells, is apparently conceaied b the tensionrelated relaxation in the preparation of tension-loaded whole tissues.