Sodium compartmentalization of the arterial wall revisited: ouabain, temperature and enzymatic effects

The sodium (Na) fractions of the dog carotid artery were identified by analyzing the effects of different procedures on 24Na washout curves. Although these never yielded more than three exponential terms, four Na fractions were identified. The fast-exchanging component amounted to 73 mmoles Na/kg w.wt., followed the kinetics of diffusion in a flat sheet with a diffusion coefficient of 6.9 X 10(-6) cm2 X s-1, and remained unaltered under the different experimental conditions. The intermediate component exchanged with a half time (t0.5) of 5.3 min and amounted to 18 mmoles Na/kg w.wt. About one third of this (6 mmoles) was constituted by cellular Na and the remaining by non-cellular Na, probably associated with extracellular structures. These two fractions could be discriminated by: (a) decreasing the rate of exchange of the cellular fraction with ouabain or low temperature (17 degrees C); (b) cell damage by freezing and thawing combined with metabolic poisoning; (c) enzymatic digestion of extracellular structures. When procedures (a) and (c) were combined, the intermediate component entirely disappeared. A third residual component amounted to 0.6 mmoles Na/kg w.wt and exchanged with a t0.5 of 70 min. It was unaffected by cellular damage or enzymatic digestion and was masked by the cellular phase in effluxes conducted at 17 degrees C or under ouabain. Its size decreased by microscopic dissection of the dense adventitia, which is probably its source.