The dependence of the transmembrane salivary secretory potential on the external potassium and sodium concentration.

1. The submandibular gland of the cat was perfused with equi-osmolar Locke solutions of different cationic composition. The increase in acinar membrane potential (secretory potential), measured with a glass capillary micro-electrode, was recorded after intra-arterial injection of acetylcholine.2. When nearly all Na in the perfusion fluid was replaced by tetraethylammonium (TEA), the size of the secretory potentials was significantly (P < 0.001) greater than of those recorded during perfusion with normal Locke solution.3. When the K concentration in the TEA Locke solution was augmented, the size of the secretory potentials was greatly diminished. Thus at a [K](o) of 4 m-equiv/l. the size of the secretory potentials was 43.3 mV +/- 2.5 (n = 19) but at a [K](o) of 10 m-equiv/l. the size was only 24.7 mV +/- 2.0 (n = 13) and at a [K](o) of 20 m-equiv/l. the size of the secretory potentials was 12.0 mV +/- 1.0 (n = 21). When the submandibular gland was perfused with a K-free TEA Locke solution the size of the secretory potentials was 49.7 mV +/- 2.2 (n = 17).4. The size of the secretory potentials recorded during perfusion with normal (Na) Locke solution increased significantly (P < 0.001) when K was omitted from the perfusion fluid. The decrease of the size with increasing [K](o) was considerably less marked than that found during perfusion with TEA Locke solution. Increasing [K](o) by a factor of 5 diminished the size of the secretory potentials recorded in Na Locke solution by a factor of 2, whereas the size of the secretory potentials recorded in TEA Locke solution, with the same changes in [K](o), diminished by a factor of 3.5.5. The results seem to indicate that the increase in acinar membrane potential obtained after stimulation of the gland is due to an enhanced permeability of the basal acinar cell membrane to K. However, it seems that the permeability to Na is also enhanced so that the outwardly directed K current is partly short-circuited by an inward Na current.