ACETYLCHOLINE-EVOKED POTASSIUM AND SODIUM TRANSPORT IN RAT LACRIMAL SEGMENTS: EVIDENCE FOR A SODIUM-CHLORIDE CO-TRANSPORT SYSTEM

¹ School of Applied Biology, Lancashire Polytechnic, Preston PR1 2TQ

An investigation was made of the effects of acetylcholine (ACh) on transmembrane movements of potassium (K⁺) and sodium (Na⁺) in isolated segments of rat lacrimal glands. ACh elicited dose-dependent and transient increases in K⁺ concentration in the effluent (K⁺ release). The ACh-induced K⁺ outflow was unaffected by either pre-treatment of lacrimal segments with loop diuretics (frusemide, piretanide and bumetanide, all 10^-4 M) or replacement of chloride (Cl^-) in the physiological salt solution with nitrate (NO₃^-). In contrast, ACh caused a significant (P 0·001) reduction in Na⁺ concentration in the effluent (Na⁺ uptake). The ACh-evoked Na⁺ uptake was sensitive to loop diuretics and Cl^- removal. Pre-treatment of tissue with ouabain (10^-3 M) resulted in a marked sustained K⁺ release. ACh produced a further increase in K⁺ efflux in the continuing presence of ouabain. Incubation of the tissue with 10 mM-tetraethylammonium (TEA) resulted in an uptake of K⁺. The results suggest the presence of a diuretic-sensitive Na⁺-Cl^- co-transport system in lacrimal acinar cell membranes.

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