Ionic distribution in dopamine-stimulated NaCl fluid-secreting cockroach salivary glands

The compound, racemose, innervated salivary glands of the cockroach Periplaneta americana closely resemble in structure and function the mammalian salivary glands (C.R. House, Biol. Rev. 55: 417-473, 1980). The quantitative distribution of Na, K, Cl, Ca, Mg, P, and S was investigated in the P-cells secreting isotonic NaCl and in duct lumens by using electron probe X-ray microanalysis of frozen-hydrated and frozen-dried cryosections. In the unstimulated glands in vitro the cells had (mmol/l cell-H2O) Na, 10; K, 110; Cl, 39 while the primary saliva had Na, 153; K, 4; Cl, 151. With 1 mumol dopamine in the bathing Ringer solution the P-cells had Na, 25; K, 177; Cl, 58 and the primary saliva, Na, 153; K, 26; Cl, 172. During passage through the ducts, the primary saliva was modified by an absorption of NaCl: more in unstimulated than in stimulated glands. It is proposed that the cells have a Na-K-ATPase both in the apical and basal cell membrane, as in vertebrate choroid plexus, and dopamine might increase the K and Na conductance of the basal cell membrane.