Effects of mercuric ions on isolated guinea-pig ileum

The possible physiological significance of low concentrations of Hg2+ in the guinea-pig ileum has been investigated. Responses to nerve stimulation by single electrical shocks, acetylcholine (ACh), and histamine (Hi) and the response to ACh of a depolarized preparation were examined. A stimulant effect of Hg2+, in the concentration range of 10 nM-1 microM, dominated in intestine accommodated in biological saline solution. This excitatory effect was probably mainly due to stimulation of a depolarization-coupled initiation of the contraction. The inhibitory effect of Hg2+, 10 nM-1 microM, observed in depolarized muscle was presumably due to a decreased Ca2+ availability for the contractile process. In the higher concentration range, 1-100 microM, a probably direct action on the contractile elements causing irreversible deterioration of the preparation seems to be present.