Abstract
In excitable cells, cellular Na+ levels are kept low by Na-pump activity of the cell membrane. Since Na-pump activity affects vascular tone, we measured cell NA+ levels and Na-pump activity in umbilical (UA) and chorionic plate arteries (CPA) from term vaginal deliveries and compared them to “normal” adult arteries using rabbit carotid arteries (RCA). Contiguous arterial segments (2.5mg) were obtained from the various sites and used for cell Na+ measures using a LiCl wash followed by flame photometry. Na-pump activity was measured using an ouabain sensitive 86Rb uptake procedure. These results indicate that human UA & CPA contain high (CPA) to extraordinarily high (UA) cell Na+ levels compared to RCA and that resting Na-pump activity is maximally turned on in UA and elevated in CPA versus RCA. Rings of arteries isolated in-vitro and contracted with serotonin in K+free media completely relax when the NA-pump is activated with KCl. Taken together these results suggest a cellular basis for maintenance of placental vascular vasodilation.
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