Na, K, Ca, and Cl exchange in guinea pig ileum

¹ Department of Pharmacology, University of Mississippi School of Medicine, Jackson, Mississippi

Exchange of Na, K, Ca, and Cl in the tubular segment (mucosa inside) of guinea pig ileum was studied. Influx and efflux of K were estimated by the method of Keynes and Lewis to be 1.36 and 4.00 pmole cm^–2 sec^–1, respectively, which are in agreement with those given by general transfer equation. In the case of Na and Cl, fluxes estimated by both methods were not consistent with each other. This fact, as well as time course of Ca inflow, indicates a complex type of exchange of these three ions, and did not permit an accurate estimation of fluxes. Pilocarpine (5 x 10^–6 m) caused a temporary increase in K efflux, temporary decrease in K influx, and little or no effect on Na exchange during the initial 30-min interval and, after a 10-min delay, a temporary decrease in Cl efflux. The drug increased the rate of Ca exchange, presumably by releasing Ca from a bound form in the tissue. This effect is believed to be the molecular basis of pilocarpine-induced contraction.