title: Evidence for a sodium electrogenic pump in airway smooth muscle.
abstract: We tested the hypothesis that the resting membrane potential (Em) of guinea pig and bovine airway smooth muscle (ASM) (m. trachealis transversus) might be influenced by a Na+ electrogenic pump. To determine the Em of ASM, glass microelectrodes filled with 3 M KCI and offering an impedance between 40 and 80 M omega were used. After incubation a normal oxygenated physiological salt solution (PSS) [pH, 7.38 +/- 0.02 (SD); temp, 37 +/- 0.5 degrees 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 that a) ouabain (10(-5) M), a specific inhibitor of the Na+ pump, causes depolarization of ASM in both species; b) exposure of ASM to a K+-free solution resulted in a similar depolarization followed by a hyperpolarization; c) exposure to normal PSS after "Na+ loading" resulted in significant hyperpolarization of ASM when these preparations were returned to normal PSS; and d) Em of ASM decreased on exposure to a low temperature (21, 25, and 29 degrees C) and increased at a high temperature (40 degrees C). It is concluded that an active electrogenic pump is present in guinea pig and bovine airway smooth muscle.
mesh_terms: D000818:Animals; D002417:Cattle; D006168:Guinea Pigs; D007473:Ion Channels; D008297:Male; D008564:Membrane Potentials; D009130:Muscle, Smooth / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000502:physiology; D014132:Trachea / Q000166:cytology / Q000187:drug effects / Q000502:physiology
chemical_list: D007473:Ion Channels; D010042:Ouabain; D011188:Potassium