Maintenance of a stable internal environment within complex organisms requires specialized cells that sense changes in the extracellular concentration of specific ions (such as Ca2+). Although the molecular nature of such ion sensors is unknown, parathyroid cells possess a cell surface Ca(2+)-sensing mechanism that also recognizes trivalent and polyvalent cations (such as neomycin) and couples by changes in phosphoinositide turnover and cytosolic Ca2+ to regulation of parathyroid hormone secretion. The latter restores normocalcaemia by acting on kidney and bone. We now report the cloning of complementary DNA encoding an extracellular Ca(2+)-sensing receptor from bovine parathyroid with pharmacological and functional properties nearly identical to those of the native receptor. The novel approximately 120K receptor shares limited similarity with the metabotropic glutamate receptors and features a large extracellular domain, containing clusters of acidic amino-acid residues possibly involved in calcium binding, coupled to a seven-membrane-spanning domain like those in the G-protein-coupled receptor superfamily.

Developmental lung biology is a field that has the potential for significant human impact: lung disease at the extremes of age continues to cause major morbidity and mortality worldwide. Understanding how the lung develops holds the promise that investigators can use this knowledge to aid lung repair and regeneration. In the decade since the “molecular embryology” of the lung was first comprehensively reviewed, new challenges have emerged—and it is on these that we focus the current review. Firstly, there is a critical need to understand the progenitor cell biology of the lung in order to exploit the potential of stem cells for the treatment of lung disease. Secondly, the current familiar descriptions of lung morphogenesis governed by growth and transcription factors need to be elaborated upon with the reinclusion and reconsideration of other factors, such as mechanics, in lung growth. Thirdly, efforts to parse the finer detail of lung bud signaling may need to be combined with broader consideration of overarching mechanisms that may be therapeutically easier to target: in this arena, we advance the proposal that looking at the lung in general (and branching in particular) in terms of clocks may yield unexpected benefits.

Modulation of calcium-sensitive potassium (BK) channels by oxygen is important in several mammalian tissues, and in the carotid body it is crucial to respiratory control. However, the identity of the oxygen sensor remains unknown. We demonstrate that hemoxygenase-2 (HO-2) is part of the BK channel complex and enhances channel activity in normoxia. Knockdown of HO-2 expression reduced channel activity, and carbon monoxide, a product of HO-2 activity, rescued this loss of function. Inhibition of BK channels by hypoxia was dependent on HO-2 expression and was augmented by HO-2 stimulation. Furthermore, carotid body cells demonstrated HO-2-dependent hypoxic BK channel inhibition, which indicates that HO-2 is an oxygen sensor that controls channel activity during oxygen deprivation.

The maintenance of a stable extracellular concentration of ionized calcium depends on the integrated function ofa number of specialized cells (e.g., parathyroid and certain kidney epithelial cells). We recently identified another G protein-coupled receptor (BoPCaR1) from bovine parathyroid that responds to changes in extracellular Ca2+ within the millimolar range and provides a key mechanism for regulating the secretion of parathyroid hormone. Using an homologybased strategy, we now report the isolation of a cDNA encoding an extracellular Ca2+/polyvalent cation-sensing receptor (RaKCaR) from rat kidney. The predicted RaKCaR protein shares 92% identity with BoPCaRl receptor and features a seven membrane-spanning domain, characteristic of the G protein-coupled receptors, which is preceded by a large hydrophilic extracellular NH2 terminus believed to be involved in cation binding. RaKCaR cRNA-injected Xenopus oocytes responded to extracellular Ca2 , Mg2+, Gd3l, and neomycin with characteristic activation of inositol phospholipiddependent, intracellular Ca2+-induced Cl-currents. In rat kidney, Northern analysis revealed RaKCaR transcripts of 4 and 7 kb, and in situ hybridization showed localization primarily in outer medulla and cortical medullary rays. Our results provide important insights into the molecular structure of an extracellular Ca2+/polyvalent cation-sensing receptor in rat kidney and provide another basis on which to understand the role of extracellular divalent cations in regulating kidney function in mineral metabolism.The kidney plays key roles in Ca2+ (1) and Mg2+ (2) The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.While the mechanism(s) whereby [Ca2+]0 (or other divalent cations) exert these effects on kidney cells is unknown, considerable indirect evidence had accumulated over the past decade to suggest that [Ca2+]0 regulates PTH secretion from parathyroid cells through a cell-surface "receptor-like" mechanism coupled to intracellular effectors (i.e., G proteins and, in turn, cAMP metabolism and inositol phospholipid (1, 13). We recently isolated by expression cloning a 5.3-kb cDNA, BoPCaR1, encoding another G protein-coupled, Ca2+/ polyvalent cation-sensing receptor from bovine parathyroid. The further demonstration that mutations in the gene for the extracellular Ca2+/polyvalent cation-sensing receptor is responsible for familial hypocalciuric hypercalcemia and severe neonatal hyperparathyroidism (14) provided compelling evidence for the role of this Ca2+ sensor in regulating PTH secretion. Interestingly, these individuals also show normal maximal renal concentrating ability despite their hypercalcemia (15), suggesting an altered sensitivity to the renal effects of increased [Ca2+]0.Using an approach based on homology to bovine parathyroid calcium-sensing receptor 1 (BoPCaR1), we now describe the sequence, functional and pharmac...