Effects of cyclopiazonic acid, a novel Ca²⁺‐ATPase inhibitor, on contractile responses in skinned ileal smooth muscle

Abstract

1 Effects of cyclopiazonic acid (CPA), a specific inhibitor of the Ca2+-ATPase in sarcoplasmic reticulum (SR) of skeletal and cardiac muscles, on contractile responses induced by Ca2"-release from intracellular storage sites were examined in the longitudinal smooth muscle strip of the guinea-pig ileum skinned with J3-escin.2 Ca2+-loading of storage sites (Ca2'-uptake) was performed in pCa 6.3 solution. The amount of Cat aken up was monitored by use of the amplitude of contraction following application of 25 mM caffeine or 25 gM inositol 1,4,5-trisphosphate (IP3). 3 Contractile responses to caffeine or IP3 were reduced or abolished when the preceding Ca2+-uptake was performed in the presence of 0.1-10g M CPA. The dose of CPA required to inhibit the contraction induced by caffeine or IP3 by 50% was approximately 0.6 gM. The CPA-sensitive Ca2"-uptake completely depended upon the presence of ATP in the solution during Ca2+-uptake.4 When 1 gM CPA was added after Ca2"-uptake, the subsequent caffeine-or IP3-induced contraction was not significantly affected by the presence of CPA. 5 Acetylcholine-induced contraction was also almost abolished when the preceding Ca2+-uptake was performed in the presence of 10gM CPA. 6 The relationship between pCa and contraction was not affected by the presence of 10gM CPA in skinned fibres where Ca2+ storage sites had been destroyed by treatment with A23187. The enhancement of contraction in pCa 6.0 solution by calmodulin was not affected by 1O gM CPA.7 These results suggest that CPA selectively inhibits ATP-dependent Ca2"-uptake into intracellular storage sites in skinned ileal smooth muscle strips. CPA appears to be a potent, reversible, and very specific inhibitor of the Ca2+-pump in the storage sites of smooth muscle, and is an extremely valuable pharmacological tool.

Resveratrol Inhibits Nicotinic Stimulation-Evoked Catecholamine Release from the Adrenal Medulla

“…It has been shown that Ca 2＋ -uptake into intracellular storage sites susceptible to caffeine (Ilno, 1989) is almost completely abolished by treatment with cyclopiazonic acid during the proceeding of Ca 2＋ load (Suzuki et al, 1992). This is consistent with the findings obtained in exposed smooth muscle fibers of the longitudinal layer of the guinea-pig ileum, where Ca 2＋ -uptake was also inhibited by cylopiazonic acid (Uyama et al, 1992). Suzuki and his coworkers (1992) have shown that cyclopiazonic acid easily penetrates into the cytoplasm through the plasma membrane and reduces Ca 2＋ -ATPase activity in sarcoplasmic/endoplasmic reticulum, resulting in increase in the subsequent Ca 2＋ release from those storage sites.…”

Properties of spontaneous depolarizations in circular smooth muscle cells of rabbit urethra

“…First, STDs are unlikely to be of neurogenic origin as they were not inhibited by atropine, phentolamine, guanethidine or tetrodotoxin. Most importantly they were abolished by BAPTA/ AM indicating that they are not due to spontaneous release of transmitter which, as shown in studies on other tissues, is not inhibited by chelation of [Ca2+]i (e.g., Hunt et al, 1994 (Siedler et al, 1989;Uyama et al, 1992). Procaine inhibits the release of Ca21 from store sites, by preventing Ca2+-induced Ca2+-release (CICR; Itoh et al, 1981).…”

Regenerative potentials evoked in circular smooth muscle of the antral region of guinea‐pig stomach

“…2) or CPA (Fig. 9), which disrupts the internal storage of Ca¥ in smooth muscle (Uyama et al 1992), but both persisted in the presence of either nifedipine or Co¥. Presumably the increase in [Ca¥]é triggers the nifedipine-resistant component of contraction ( Fig.…”