Characterization of calcium transport in the luminal and the basolateral membrane from kidney cortex of hypercalcemic rats bearing the Walker 256 carcinosarcoma.
The Walker 256 (W256) carcinosarcoma did not significantly modify calcium uptake by brush border membrane (BBM) vesicles in the kidney of the host rat, compared with that in membranes isolated from control animals. However, it showed a tendency to increase at near equilibrium in W256 tumor-host rats, associated with a decreased BBM protein content. ATP-dependent calcium influx by basolateral membrane (BLM) vesicles from W256 tumor-bearing rats was also increased compared with that in control BLM. This stimulation was due to a decreased Km for calcium. Passive calcium permeability or the Na+/Ca2+ exchanger were unchanged in BLM from W256 tumor-host rats compared with control BLM. Pre-stimulation of control rat cortical tubules with either 10(-7) M parathyroid hormone-related protein (PTHrP) (1-34) or 10(-4) M N6,2'-O-dibutiryl cyclic AMP before BLM isolation, did not modify the ATP-dependent calcium uptake by BLM vesicles compared with control membranes. However, our results do not rule out that the stimulated ATP-dependent calcium influx in BLM from W256 tumor-host rats could be mediated by the interaction among PTHrP and other humoral factors. Our findings suggest a possible mechanism for the increased renal calcium reabsorption in this animal model for humoral hypercalcemia of malignancy.
de Miguel
F
F
Laboratorio de la Unidad Metabólica, Fundación Jiménez Díaz, Madrid, Spain.
Esbrit
P
P
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002279:Carcinoma 256, Walker / Q000150:complications / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D006934:Hypercalcemia / Q000150:complications / Q000378:metabolism*; D007672:Kidney Cortex / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008854:Microscopy, Electron; D008871:Microvilli / Q000378:metabolism; D044162:Parathyroid Hormone-Related Protein; D011506:Proteins / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D014638:Vanadates / Q000494:pharmacology
D044162:Parathyroid Hormone-Related Protein; D011506:Proteins; D014638:Vanadates; D003994:Bucladesine; D000255:Adenosine Triphosphate; D002118:Calcium