A role for a background sodium current in spontaneous action
potentials and secretion from rat lactotrophs.
Sankaranarayanan, Sethuraman, and Steven M. Simasko.
Program in Neuroscience, Department of Veterinary Comparative
Anatomy Physiology and Pharmacology, College of Veterinary Medicine,
Washington State University, Pullman, WA 99164-6520
APStracts 3:0249C, 1996.
We have addressed the role of depolarizing background currents in
maintaining spontaneous action potentials and spontaneous secretion
from rat lactotrophs in primary culture using the perforated-patch
variation of whole-cell patch-clamp techniques, measurements of
cytosolic calcium using fura-2, and secretion measurements using the
reverse-hemolytic plaque assay. Replacement of bath sodium with Tris
or N-methyl-D-glucamine caused a dramatic hyper-polarization of the
cells, a cessation of spontaneous action potentials, and an increase
in input resistance of cells. Tetrodotoxin had no effect on
spontaneous action potentials and removal of bath calcium stopped
spiking but did not hyperpolarize the cells. The hyperpolarization in
response to removal of bath sodium was associated with a decrease in
cytosolic calcium levels. Finally, removal of bath sodium caused a
decrease in spontaneous secretion of prolactin from lactotrophs.
These data suggest that a background sodium current is essential to
drive the membrane to threshold for firing spontaneous calcium
-dependent action potentials in lactotrophs. This, in turn, results in
elevated intracellular calcium that support spontaneous secretion of
prolactin from these cells.
Received 28 February 1996; accepted in final form 25 June 1996.
APS Manuscript Number C109-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 21 August 1996