. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 10|iM SNAP t 10 nM NAP 5 min Figure 1. NO-donors cause relaxation of the cardiac stomach, (a) Hydroxylamine; gain 1. (b) SNOG; gain 5. (c) SNAP; gain 7. (d) NAP, which is chemically identical to SNAP apart from the absence of a NO moiety, does not cause relaxation; gain 5. [W = wash] In (c) and (d) there is a slight decrease in baseline tension during the course of the experiments, but the responses to SNAP and NAP, respectively, are clearly very different. bition of SGC activation by endogenous NO. To investi- gate the mode
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 10|iM SNAP t 10 nM NAP 5 min Figure 1. NO-donors cause relaxation of the cardiac stomach, (a) Hydroxylamine; gain 1. (b) SNOG; gain 5. (c) SNAP; gain 7. (d) NAP, which is chemically identical to SNAP apart from the absence of a NO moiety, does not cause relaxation; gain 5. [W = wash] In (c) and (d) there is a slight decrease in baseline tension during the course of the experiments, but the responses to SNAP and NAP, respectively, are clearly very different. bition of SGC activation by endogenous NO. To investi- gate the mode of action of ODQ on the cardiac stomach, we tested ODQ in combination with exogenous NO re- leased by the NO-donor SNAP. First SNAP was tested alone at a concentration (10 /jM) at which it consistently causes relaxation of the cardiac stomach (Fig. 3a). Then, after washing, the cardiac stomach was incubated with lO^M ODQ for 15 min before applying a second dose of 10 ^M SNAP (Fig. 3b). ODQ caused almost complete inhibition (^ in Fig. 3b) of the relaxing effect of SNAP. After washing out of the ODQ, SNAP was tested a third time and in the absence of ODQ the normal re- laxing effect of 10 ijM SNAP was restored (Fig. 3c). The mean percentage inhibition by \0 jjM ODQ on the re- laxing effect of 10 ijM SNAP in hve experiments on dif- ferent preparations was ± '7c (Fig. 3d). A mean inhibition of was observed in two other experi- ments using 3 ^M ODQ (data not shown). The experiments described so far indicate that NO causes relaxation of the cardiac stomach by activating SGC. In the presence of the SGC inhibitor ODQ, the relaxing effect of endogenous NO is blocked, leading to contraction. However, this provides only indirect evi-. t t 1 |iM ODQ 3 |iM ODQ vehicle had no effect on muscle tone. Doses of 1 fjM and 3 ^M ODQ had no effect on cardiac stomach tone, but 10 fiM ODQ consistently caused contraction (Fig. 2b), However, the delay in the onset of contraction and
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