Hormone-stimulated Ca2+ reabsorption in rabbit kidney cortical collecting system is cAMP-independent and involves a phorbol ester-insensitive PKC isotype.
BACKGROUND
Hormones such as parathyroid hormone (PTH), arginine vasopressin (AVP), and prostaglandin E2 (PGE2) are generally believed to act through cAMP to stimulate active Ca2+ reabsorption in the distal part of the nephron.


METHODS
This study investigates the relationship between intracellular cAMP levels and the rate of Ca2+ reabsorption in immunodissected rabbit connecting and cortical collecting tubules cultured to confluence on permeable supports.


RESULTS
Basolateral PTH, AVP, and PGE2 and apical adenosine dose dependently increased Ca2+ reabsorption from 48 to 110 nmol. hr-1. cm-2. Measurement of intracellular cAMP levels revealed that in the case of PTH and AVP, the dose-response curve for the increase in cAMP virtually matched that for transcellular Ca2+ transport. By contrast, with PGE2, this curve was shifted two decades to the right, whereas in the case of adenosine, no increase in cAMP was observed. The results with the latter two hormones disagree with the classic concept that Ca2+ reabsorption is stimulated via a cAMP-dependent mechanism. Furthermore, the potent adenylyl cyclase inhibitor 2', 5'-dideoxyadenosine (DDA; 100 micrometers) suppressed the PTH- and AVP-induced increase in cAMP completely without affecting Ca2+ reabsorption. Similarly, concentrations of PGE2, which maximally stimulated Ca2+ reabsorption without increasing cAMP, were not inhibited by DDA. The specific protein kinase C (PKC) inhibitor chelerythrine (5 micrometers) inhibited PTH-, AVP-, PGE2-, and adenosine-stimulated Ca2+ reabsorption by 77%, 67%, 79%, and 100%, respectively. Down-regulation of phorbol ester-sensitive PKC isotypes by prolonged (120 hr) treatment with 0.1 micrometers 12-O-tetradecanoylphorbol 13-acetate did not interfere with the inhibitory action of chelerythrine on hormone-stimulated Ca2+ transport.


CONCLUSIONS
PTH, AVP, PGE2, and adenosine stimulate Ca2+ reabsorption via a pathway that is independent of cAMP and that involves a phorbol ester-insensitive PKC isotype.
Hoenderop
J G
JG
Departments of Biochemistry and Cell Physiology, University of Nijmegen, Institute of Cellular Signalling, Nijmegen, The Netherlands. J.Hoenderop@bioch.kun.nl
De Pont
J J
JJ
Bindels
R J
RJ
Willems
P H
PH
D000241:Adenosine / Q000494:pharmacology; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D046508:Culture Techniques; D000242:Cyclic AMP / Q000378:metabolism; D016048:Dideoxyadenosine / Q000494:pharmacology; D015232:Dinoprostone / Q000494:pharmacology; D006728:Hormones / Q000494:pharmacology*; D007424:Intracellular Fluid / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D007527:Isoenzymes / Q000378:metabolism; D007672:Kidney Cortex / Q000187:drug effects* / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000187:drug effects* / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D011817:Rabbits; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D006728:Hormones; D007527:Isoenzymes; D010281:Parathyroid Hormone; D001127:Arginine Vasopressin; D016048:Dideoxyadenosine; D000242:Cyclic AMP; D011493:Protein Kinase C; D000241:Adenosine; D015232:Dinoprostone; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium