Evidence for a sodium electrogenic pump in airway smooth muscle

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Abstract
The hypothesis that the resting membrane potential (Em) of guinea pig and bovine airway smooth muscle (ASM) (musculus trachealis transversus) might be influenced by a Na+ electrogenic pump was tested. To determine the Em of ASM, glass microelectrodes filled with 3 M KCl and offering an impedance of 40-80 M.OMEGA. were used. After incubation, a normal oxygenated physiological salt solution (PSS) [pH, 7.38 .+-. 0.02 (SD); temperature, 37 .+-. 0.5.degree. C (SD)] for 60 min, the Em of guinea pig ASM was -62.5 .+-. 1.25 (SE) mV (successful impalement of 437 cells of 37 tracheal preparations from 37 different animals) and that of bovine ASM was -60.0 .+-. 1.5 mV (successful impalement of 306 cells of 26 tracheal preparations from 26 different animals). Tracheal preparation consisted of 10-mm-long segments of cervical or intrathoracic portions of the trachea. Approximately 30% of the cells of both species exhibited spontaneous electrical activity (slow waves). Studies to determine whether an electrogenic pump was present revealed the following: ouabain (10-5 M), a specific inhibitor of the Na+ pump, causes depolarization of ASM in both species; exposure of ASM to a K+-free solution resulted in a similar depolarization followed by a hyperpolarization; exposure to normal PSS after Na+ loading resulted in significant hyperpolarization of ASM when these preparations were returned to normal PSS; Em of ASM decreased on exposure to a low temperature (21, 25 and 29.degree. C) and increased at a high temperature (40.degree. C). An active electrogenic pump is present in guinea pig and bovine airway smooth muscle.