Journal of Neurophysiology, Vol 69, Issue 4 1363-1367, Copyright © 1993 by APS
Transient extracellular volume reduction in neural lobe of rat hypophysis in response to neural stalk stimulation in vitro and its relationship to extracellular potassium
W. E. Armstrong and M. E. Rice
Department of Anatomy and Neurobiology, University of Tennessee, Memphis.
1. Using ion-sensitive microelectrodes, a transient reduction in the local
volume of neural lobe extracellular space was found to accompany the
elevation in extracellular potassium induced by stimulation of the neural
stalk. The volume decrease and potassium increase had similar
stimulus-response curves when stimulus frequency was varied from 1 to 40
Hz, with maximal response at 20 Hz. The curves for stimulus duration
diverged, as a near maximal potassium response was reached in 4-16 s with a
20-Hz stimulus, while the extracellular volume decrease was maximal at 64
s. 2. The volume decrease, but not the potassium increase, was strongly
inhibited by lowering bath temperature and moderately inhibited by
furosemide and by lowering extracellular chloride concentration. Both the
volume and the potassium response were enhanced by ouabain. 3. In
conclusion, shrinkage of the local extracellular space in neural lobe
during nerve activity is mediated by a metabolically active process which
is only partially dependent upon extracellular chloride concentration and
anion-cation co-transport, but is relatively independent of Na(+)-K+ pump
activity. A transient shrinkage in extracellular space during increased
neurohypophysial nerve activity would be expected to play a role in hormone
diffusion, ion buffering, and extracellular current flow.
