Intracellular concentrations of sodium, potassium and chloride in the lactating mammary gland and their relation to the secretory mechanism.
1. The intracellular (I.C.) concentrations of Na, K and Cl in mammary cells from lactating guinea-pigs have been calculated from the analysis of fresh tissue and the measurement of the extracellular (E.C.) space with [(14)C]sucrose and the milk content with [(14)C]lactose.2. Assuming that alveolar milk has the same concentration as teat milk, the intracellular concentrations were calculated to be K 115, Na 42 and Cl 66 m-equiv. l(-1) intracellular water.3. Intracellular concentrations were also calculated in slices incubated in Krebs-bicarbonate medium plus glucose. There was a large increase in the sucrose (E.C.) space and a rise in total tissue [Na] and [Cl]. On the assumption that the medium had equilibrated with the milk space as well as the E.C. space, the calculated I.C. concentrations of Na (43 m-equiv. l(-1)), and Cl (62) were very similar while [K] was somewhat higher (143 m-equiv. l(-1)I.C. water).4. The calculated I.C. concentrations of all three ions are all higher than in milk but the ratios between them are almost identical.5. Similar figures for the I.C. concentrations of Na, K and Cl have been obtained in the goat, cow and sheep mammary tissue incubated in vitro.6. Moderate changes in the concentrations of Na, K and Cl in the external medium had no effect on cell composition but during incubation without ions [(14)C]sucrose became distributed throughout the total tissue water indicating that sucrose had entered the I.C. compartment.7. Acetazolamide (10(-2)M), aldosterone (1.4 x 10(-6)M) and, in some experiments, lack of glucose lowered I.C. [Cl(-)], but oxytocin, vasopressin and low doses of insulin had no effect.8. The data are difficult to reconcile with the hypothesis of Zaks, Natochin, Sokolova, Tanasiichuk & Tverskoi (1965) that freshly secreted milk has the ionic composition of plasma.9. Comparison of I.C. ion concentrations and the membrane potential between the cells and milk suggests that Na(+) and K(+) are passively distributed across the apical membrane but that Cl(-) must be actively held in the cells. Across the basal membrane the data are consistent with the presence of a Na(+) pump and with Kinura's (1969) detection of a Na:K ATPase on the basal and lateral membranes. In addition another inward-facing Cl(-) pump may exist at this site.
D000086:Acetazolamide / Q000494:pharmacology; D000450:Aldosterone / Q000494:pharmacology; D000818:Animals; D002247:Carbon Isotopes; D002417:Cattle; D002712:Chlorides / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D005947:Glucose / Q000494:pharmacology; D006041:Goats; D006168:Guinea Pigs; D007328:Insulin / Q000494:pharmacology; D007774:Lactation; D007785:Lactose / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000378:metabolism* / Q000502:physiology; D008564:Membrane Potentials; D008892:Milk / Q000502:physiology; D010121:Oxytocin / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D011247:Pregnancy; D012756:Sheep; D012964:Sodium / Q000378:metabolism*; D013395:Sucrose / Q000378:metabolism; D013997:Time Factors; D014667:Vasopressins / Q000494:pharmacology
D002247:Carbon Isotopes; D002712:Chlorides; D007328:Insulin; D014667:Vasopressins; D000450:Aldosterone; D010121:Oxytocin; D013395:Sucrose; D012964:Sodium; D005947:Glucose; D007785:Lactose; D000086:Acetazolamide; D011188:Potassium