AJP - Endocrinology and Metabolism, Vol 238, Issue 2 167-E173, Copyright © 1980 by American Physiological Society
Kinetic analysis of calcium distribution in rat anterior pituitary slices
C. M. Moriarty
A kinetic analysis of exchangeable calcium associated with rat anterior
pituitary slices was carried out. Slices were permitted to accumulate 45Ca
for 1 h, and then a desaturation experiment was initiated. The resulting
data was represented as a polyexponential function and analyzed with a
weighted nonlinear least-squares method. The resulting coefficients and
exponents were used to determine, at the steady state, the size of each
calcium compartment, the unidirectional fluxes into and out of each
compartment, and the corresponding rat constants. Three kinetically
distinguishable compartments were defined. The first compartment exchanges
with a half-time slower than calcium free in the extracellular space and
can be removed by a 1.5-min exposure to Ca-free EGTA media suggesting that
this calcium is bound in the extracellular matrix perhaps to the cell
surfaces. The second compartment is intracellular and does not contain
calcium accumulating structures such as mitochondria or microsomes. The
third compartment has many of the characteristics associated with these
organelles. Experiments were performed with two pituitary secretagogues,
elevated K+ and ouabain, to assess changes in the study-state calcium
distribution associated with enhanced secretion.
