The effect of Mn 2+, Zn 2+, Ba 2+ and Ca 2+ on spontaneous motility in sheep duodenum in vitro

Abstract

1. 1. The effects of several ions, Mn 2+, Zn 2+, Ba 2+ and Ca 2+, on spontaneous motility were investigated in longitudinal smooth muscle strips from sheep duodenum, in vitro 2. 2. Mn 2+ (0.5–1.5 mM) and Zn 2+ (0.5–5 mM) inhibited both the amplitude and frequency of motility in Krebs solution and in Ca 2+-free medium. 3. 3. Ba 2+(0.5–5 mM) evoked three types of contractile responses: (i) an increase in the frequency and a reduction of the amplitude of spontaneous contractions; (ii) a slight increase in muscle tone of the phasic contractions; and (iii) a rapid initial phasic contraction followed by slowly fading contraction. Ca 2+ induced two kinds of responses in spontaneous motility: (i) a fast phasic contraction, followed by an increase in the amplitude and frequency of phasic contractions with no changes in its tone; and (ii) an increase in the amplitude of contractions. 4. 4. The Ba 2+-induced contractions were inhibited by EDTA, verapamil and diltiazem, but were not modified by sodium nitroprusside. The Ca 2+-induced contractions were reduced by verapamil and diltiazem. 5. 5. Our results show that Mn 2+ and Zn 2+ behave as inhibitors of sheep duodenum motility. In contrast, Ba 2+ and Ca 2+ stimulate motility. It is suggested that Ba 2+ can penetrate the cells through voltage-dependent Ca 2+ channels and behave as a partial substitute for Ca 2+.