Inhibitory effect of bassianolide, a cyclodepsipeptide, on drug-induced contractions of isolated smooth muscle preparations.

Bassianolide (BASS) is a cyclodepsipeptide isolated from cultured mycelia of Beauveria bassiana and is pathogenic to insects. In a longitudinal muscle preparation from guinea pig ileum, 10(-6) M BASS almost irreversibly inhibited an isotonic contraction induced by acetylcholine (ACH) and made the dose-response curve shift in parallel to the right (pA2: 7.6). It also inhibited the contractions induced by carbachol, pilocarpine, histamine, 5-hydroxytriptamine (5-HT) and prostaglandin E2, but did not inhibit the contraction induced by barium or a high concentration (40-60 mM) of potassium (high K). When applied to the guinea pig vas deferens, 10(-8) - 10(-7) M BASS inhibited an isometric contraction induced by norepinephrine (NE) (3 x 10(-6) - 10(-5) M), phenylephrine (3 x 10(-6) - 10(-5) M) or ACH (10(-6) - 10(-5) M). When the contractions of the three agonists exceeded the concentrations mentioned above, BASS failed to exert an inhibitory effect upon any of these agonists. It also inhibited the contraction caused by carbachol and histamine, but did not inhibit that induced by barium or high K. BASS itself failed to cause the contraction or relaxation of both muscle preparations. From these results, it is suggested that BASS inhibits the contraction induced by an agonist which acts upon selective sites of smooth muscle cells, but which does not inhibit a contraction induced by an agonist that has an effect on non-selective sites of cells.