Effects of depolarizing concentrations of K+ and reduced osmotic pressure on 45Ca2+ accumulation by the rostral pars distalis of the tilapia (Oreochromis mossambicus).
The accumulation of 45Ca2+ into tilapia prolactin (PRL) tissue was examined under conditions which alter prolactin release. In initial experiments, PRL tissue was incubated in medium containing 12 microCi/ml 45Ca2+ in hyperosmotic medium (355 mOsmolal). Under these conditions, 45Ca2+ accumulated steadily, reaching a plateau within 15-20 min. Subsequent exposure to La3+, which displaces Ca2+ from superficial pools in a wide variety of tissues, rapidly (within 5 min) removed nearly 70% of the 45Ca2+ associated with the tissue. Following this initial removal of 45Ca2+, the level of 45Ca2+ in the PRL tissue remained constant, and is referred to as the La3(+)-resistant pool of Ca2+. This pool of Ca2+ is thought to reflect the entry rate of Ca2+ from extracellular sources. Prolactin tissue exposed to hyposmotic medium or to depolarizing [K+], which stimulates PRL release, significantly increased 45Ca2+ accumulation in this La3(+)-resistant pool. These results indicate that reduced osmotic pressure and depolarization may alter release from tilapia PRL cells, in part, through their ability to increase the entry of extracellular Ca2+.
Richman
N H
NH
Department of Zoology, University of Hawaii, Honolulu 96822.
Helms
L M
LM
Ford
C A
CA
Benishin
C
C
Pang
P K
PK
Cooke
I M
IM
Grau
E G
EG
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005399:Fishes / Q000378:metabolism*; D066298:In Vitro Techniques; D009997:Osmotic Pressure; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology*
D011188:Potassium; D002118:Calcium