Calcium Sensitizers Isolated from the Edible Pine Mushroom, Tricholoma matsutake (S. Ito & Imai) Sing
1 Three lactam compounds were isolated from the fruiting body of Tricholoma matsutake (S. Ito & Imai) Sing., an edible mushroom, and their structures were identifi ed as cyclo- S-proline-R-leucine (), hexahydro-2H-azepin-2-one (2), and butyl 5-oxo-2-pyrrolidine carboxylate (3) by chemical, physicochemical, and spectral evidence. In in vitro screening tests, compounds 1 and 2 acted as calcium sensitizers in ventricular cells from rat. Further studies on compounds 1 and 2 in ex vivo isolated right atria showed positive inotropic effects without disturbing the spontaneous beating rate. The inotropic effect of compounds 1 and 2 could be greatly abolished by pretreating the myocardium in Ca2+-free solution. These fi ndings indicate that compounds 1 and 2 can signifi cantly increase the calcium ion concentration ([Ca2+]i) in myocytes, which is greatly dependent on the infl ux of extracellular Ca2+.