CALCIUM CHANNELS AND INTESTINAL FLUID SECRETION - AN EXPERIMENTAL-STUDY IN-VIVO IN RATS

Several mechanisms involved in nervous secretory reflex(es) of the ent eric nervous system may be dependent on the flux of calcium across the plasma membrane, which may be controlled by voltage-gated calcium cha nnels. In this study, we investigated the importance of plasma membran e calcium channels for intestinal fluid secretion. Two types of studie s were performed, in which intestinal net fluid transport in anaesthet ized rats was followed with a gravimetric method. First, the effects o n intestinal fluid transport of placing A23187, a calcium ionophore, i n the intestinal lumen was studied. A23187 induced in a dose-dependent manner a net fluid secretion, which was abolished by giving hexametho nium (10 mg kg(-1) body wt) i.v. or placing lidocaine (1% solution) on the intestinal serosa. Nifedipine (5.75 mu mol kg(-1) body wt i.v.) a lso abolished the fluid secretion caused by the ionophore. in the seco nd study, the effects of various calcium channel blockers (gadolinium chloride, nifedipine, verapamil) were tested on the cholera toxin-indu ced secretion. It was attenuated by luminal application of gadolinium chloride (1-10 mM) or nifedipine (10-200 mu M). Intravenously administ ered nifedipine (2.5-5.75 mu mol kg(-1) body wt) abolished cholera tox in-evoked secretion dose-dependently, whereas verapamil (0.05-1 mu mol kg(-1) body wt) was without consistent effect. It is concluded that t he fluid secretion evoked by placing A23187 in the intestinal lumen in vivo was induced via an activation of the enteric nervous system. Cho lera secretion was attenuated or abolished by calcium channel blockers of the L -or N-type.