Effects of nerve stimulation on ion transport in mouse jejunum: responses to Veratrum alkaloids.
Veratrum alkaloids were used to examine the effect of neural stimulation on intestinal ion transport in full-thickness (intact) and serosally stripped (mucosal) preparations of mouse jejunum. When applied to the serosal media of mucosal preparations, veratrine or veratridine evoked a biphasic increase in transmural potential difference and short-circuit current, consisting of phasic and tonic increases of both bioelectric parameters without a change of tissue conductance; these responses were blocked by pretreatment with tetrodotoxin, but unaffected by pretreatment with atropine, naloxone or yohimbine. In ion flux experiments, neural stimulation of mucosal tissues produced changes of unidirectional fluxes that corresponded with an increase in net Cl- secretion and a reduction of net Na+ absorption, supporting a net secretory role for neurons that were associated with the intestinal mucosa. In intact jejunal preparations, neural stimulation by veratrine or veratridine caused a tetrodotoxin-sensitive reduction of basal transmural potential difference and short-circuit current and a significant increase of tissue conductance. Flux studies on intact tissues failed to reveal the ionic basis for the effects of nerve stimulation by veratridine in these tissues. Nonetheless, the neurally evoked reduction of short-circuit current was attenuated by yohimbine pretreatment, but unaffected by naloxone or atropine, suggesting an involvement of alpha-2 adrenoceptors in the mediation of this effect. These findings demonstrate the existence of endogenous neurotransmitter systems that play opposing roles in the regulation of mucosal ion transport in the small intestine of the mouse.