Na⁺ channels in membrane vesicles from intralobular salivary ducts

Electrical potential-driven ²²Na⁺ fluxes were measured in membrane vesicles prepared from male and female rat submandibular intralobular ducts. A relatively temperature-independent (Q₁₀ = 1.45 ± 0.15), amiloride- inhibitable (mean affinity constant ≃ 1 μM), rheogenic Na⁺ transport pathway was observed. The relative potency of amiloride analogues for inhibition of this pathway was amiloride > ethylisopropyl-amiloride > phenamil, similar to that of the 'low-amiloride-affinity' Na⁺ channel recently observed in a number of other tissues. These results are consistent with the existence of the apical Na⁺ channel thought to be involved in intralobular ductal salt reabsorption. No significant difference was found in the magnitude or pharmacology of electrogenic Na⁺ fluxes in vesicles prepared from male and female rat intralobular ducts, suggesting that the sexual dimorphism observed in this tissue is not reflected at the level of the apical membrane Na⁺ channel. Amiloride-sensitive ²²Na⁺ fluxes in intralobular ductal membranes were of the same magnitude as ²²Na⁺ fluxes measured in similarly prepared and assayed vesicles from the toad bladder, a tissue thought to be a rich source of amiloride-sensitive Na⁺ channels.