Stimulus-secretion coupling of parathyroid hormone release: studies of 45Ca and 86Rb fluxes.
Pieces of rat parathyroid glands were used to study fluxes of 45Ca and 86Rb. The uptake of 45Ca increased with the extracellular Ca2+ concentration up to at least 5 mM. A rise of extracellular Ca2+ had dual effects on 45Ca efflux in terms of an initial stimulation and a subsequent inhibition. However, K+ depolarization neither affected the uptake nor the efflux of 45Ca indicating a lack of voltage-dependent Ca2+ channels. The depolarization obtained with exposure to Ca2+ cannot be attributed to a decreased K+ permeability, since the 86Rb concentrating ability diminished and the efflux of the isotope increased when parathyroid pieces were exposed to a raised Ca2+ concentration. A stimulation of 86Rb efflux by the Ca2+ ionophore A-23187 indicated that the parathyroid cells possess a K+ permeability activated by cytoplasmic Ca2+. It is suggested that Ca2+ fluxes through channels sensitive to activation by Ca2+ are important both for the membrane potential and the cytoplasmic Ca2+ activity.
C
C
Wallfelt
R
R
Larsson
H
H
Johansson
J
J
Rastad
G
G
Akerström
S
S
Ljunghall
E
E
Gylfe
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002132:Calcium Radioisotopes / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects; D002478:Cells, Cultured; D003470:Culture Media; D007473:Ion Channels; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D010280:Parathyroid Glands / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000378:metabolism*; D010904:Pituitary Gland, Posterior / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D011868:Radioisotopes / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012413:Rubidium / Q000378:metabolism*
D002132:Calcium Radioisotopes; D003470:Culture Media; D007473:Ion Channels; D010281:Parathyroid Hormone; D011868:Radioisotopes; D000001:Calcimycin; D008274:Magnesium; D012413:Rubidium; D011188:Potassium; D002118:Calcium