AJP - Endocrinology and Metabolism, Vol 243, Issue 4 298-E304, Copyright © 1982 by American Physiological Society
TRH mobilizes membrane calcium in thyrotropic cells as monitored by chlortetracycline
M. C. Gershengorn and C. Thaw
Chlortetracycline (CTC), a probe of membrane-bound divalent cations, was
used to study the action of thyrotropin-releasing hormone (TRH) in mouse
pituitary thyrotropic tumor (TtT) cells in culture. Cellular fluorescence
of CTC was caused by both Ca2+- and Mg2+-CTC complexes and was influenced
by the concentration of these cations in the incubation medium. TRH, but
not other peptides, caused a rapid, transient, and concentration-dependent
decrease in the CTC fluorescence intensity; half-maximal effect occurred
with 10--30 nM TRH. The decrement in fluorescence intensity caused by TRH
was not due to enhanced loss of CTC from the cells. The decrease in
fluorescence elicited by TRH was specific for Ca2+-CTC complexes because
preincubation of the cells with 1 mM EGTA or 1 mM EDTA plus 2.05 mM Mg2+
abolished the response, whereas preincubation with 1 mM EDTA plus 2.05 mM
Ca2+ permitted the usual TRH response. Antimycin A and carbonyl cyanide
m-chlorophenylhydrazone decreased cellular ATP content to 37 +/- 1 and 32
+/- 1% of control, respectively, and abolished the TRH-induced decrease in
CTC fluorescence. We conclude that TRH displaced Ca2+ from an
energy-dependent, membrane-bound pool(s) within TtT cells and that this may
be one mechanism by which the concentration of intracellular free Ca2+ is
raised so that is couples stimulation by TRH to TSH secretion.
