Injection of bovine parathyroid poly(A)+ RNA into xenopus oocytes confers sensitivity to high extracellular calcium
Open Access
- 1 February 1994
- journal article
- research article
- Published by Oxford University Press (OUP) in Journal of Bone and Mineral Research
- Vol. 9 (2), 293-300
- https://doi.org/10.1002/jbmr.5650090219
Abstract
Parathyroid cells detect increments in the extracellular [Ca2+], which lead to substantial increases in intracellular free Ca2+ ([Ca2+]i) and, ultimately, to suppression of parathyroid hormone (PTH) secretion. To determine whether mRNA from parathyroid tissue could confer sensitivity to high extracellular Ca2+, we isolated and injected total bovine parathyroid poly(A)+ RNA into Xenopus laevis oocytes. To assess translational activity of the RNA, PTH released into the media was measured. Intact PTH was detected in the medium for ≤48 h, and injection of increasing amounts of RNA (∼0.5–50 ng/oocyte) led to the release of greater quantities of PTH. We screened for the expression of a putative Ca2+ sensor molecule by measuring 45Ca efflux from preloaded oocytes, in response to raising extracellular [Ca2+] from 0.7 to 5.7 mM. This increment in [Ca2+] stimulated 45Ca efflux by 249 ± 52 cpm over 20 min from eggs injected with parathyroid poly(A)+ RNA (n = 22). This response was significantly greater than 45Ca efflux from any group of controls exposed to the same change in extracellular Ca2+ (p < 0.02), including oocytes injected with either water, cRNA for the platelet-derived growth factor (PDGF) BB receptor, or T cell poly(A)+ RNA. Size-fractionation of poly(A)+ RNA over sucrose gradients demonstrated that mRNA, which induced responsiveness to high extracellular Ca2+, was present in fractions with transcripts of ˜5–9 kB. Injection of these fractions also conferred sensitivity to the presence of Ba2+ or Sr2+ (both at 5 mM) in the media. These findings establish that parathyroid cells express mRNA for a molecule capable of detecting changes in the extracellular divalent cation concentration. This molecule may play a role in secretory responses mediated by Ca2+ in the parathyroid.Keywords
Funding Information
- VA Merit Review
- NIH (R29 DK39594, DK43400)
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