Na,K-ATPase in resting and stimulated submandibular salivary glands in cats, studied by means of ouabain-sensitive, K(+)-dependent p-nitrophenylphosphatase activity.

Sections from normal resting submandibular glands were incubated in a p-nitrophenylphosphate substrate mixture to demonstrate Na,K-ATPase activity by light and electron microscopy. Dense deposits of reaction product occurred within the basal and lateral infoldings of striated duct cells. A similar, less heavy deposition occurred in demilune cells. Only scattered, infrequent pockets of staining occurred in association with the basal plasma membrane of central acinar cells, supporting the belief that these cells do not contribute greatly to the secretion of fluid. No reaction was detected on luminal membranes. Glands tested after sympathetic or parasympathetic nerve stimulation showed no obvious differences from resting glands. These results contrast with the previously reported paucity of immunostaining in resting demilunes with an antibody to Na,K-ATPase and the large increase in the immunostaining by these cells after parasympathetic stimulation. It is inferred that there must be an inaccessibility to immunobinding sites of Na,K-ATPase in resting glands, and that the increase in binding which occurs after parasympathetic stimulation represents a conformational change that did not affect its enzyme catalytic reaction with this substrate.