Effect of vasopressin on brain swelling at the cellular level: do astrocytes exhibit a furosemide--vasopressin-sensitive mechanism for volume regulation?

Two sets of new observations are reported: (i) astrocytes in primary cultures show an increased potassium-induced swelling in the presence of 1-100 x 10(-12) M vasopressin, whereas no similar phenomenon is found in primary cultures of neurons, and (ii) the furosemide-sensitive cotransport system for uptake of K+, Na+, and Cl-, which is known to exist in astrocytes, is absent in neurons. On the basis of these findings and observations by other investigators on transport of ions and water in the brain in vivo, a novel mechanism is suggested, according to which all boundaries of brain parenchymal tissue (perivascular astrocytic end-feet, glia limitans, and ependyma) in the absence of vasopressin are capable of performing a net uptake of K+, Na+, and Cl- without uptake of water, and that the resulting hyperosmolarity in the presence of vasopressin leads to water uptake (cell swelling), which causes a reduction in the amount of water in the interstitial fluid and thus an increase in extracellular concentrations of ions.