Parathyroid hormone stimulates ecto-5'-nucleotidase activity in renal epithelial cells: role of protein kinase-C.

The role of protein kinase C (PKC) in regulating cytosolic Ca2+ concentrations ([Ca2+]i) and parathyroid hormone (PTH) secretion was studied in bovine parathyroid cells rendered deficient in PKC activity by incubation with phorbol 12-myristate 13-acetate (PMA). Pretreatment with PMA caused a time- and concentration-dependent loss of functional PKC activity as assessed by the failure of [Ca2+]i and PTH secretion to respond to the subsequent addition of PKC activators or the inhibitor staurosporine. Pretreatment for 24 h with 1 microM PMA caused a loss of 85% of the total and 98% of the cytosolic PKC activity. Cells so pretreated were considered to be "PKC downregulated." Increasing the concentration of extracellular Ca2+ or Mg2+ caused corresponding increases in [Ca2+]i that were similar in control and in PKC-downregulated cells. PTH secretion regulated by extracellular Ca2+ or Mg2+ was likewise similar in control and PKC-downregulated cells. Stimulus-secretion coupling is thus unimpaired in parathyroid cells deficient in PKC activity. Cytosolic Ca2+ responses remained depressed in cells incubated for 24 h with low concentrations of PMA (30 or 100 nM). However, under these conditions, extracellular Ca2+ still suppressed PTH secretion similarly to control cells. These results reveal a dissociation between cytosolic Ca2+ and PTH secretion and suggest that signals other than cytosolic Ca2+ are involved in the regulation of PTH secretion.

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Role of protein kinase C in beta 2-adrenoceptor function in cultured rat proximal tubule epithelial cells

AJP Renal Physiology ◽

10.1152/ajprenal.1997.273.2.f193 ◽

1997 ◽

Vol 273 (2) ◽

pp. F193-F199 ◽

Cited By ~ 2

Author(s):

H. Singh ◽

S. L. Linas

Keyword(s):

Protein Kinase C ◽

Protein Kinase ◽

Epithelial Cells ◽

Atpase Activity ◽

Proximal Tubule ◽

Sodium Transport ◽

Kinase C ◽

Beta 2 ◽

Rat Proximal Tubule

Renal sodium excretion is regulated by the adrenergic system. We recently demonstrated the presence of functional beta 2-adrenoceptors (beta 2-AR) in cultured rat proximal tubule epithelial cells beta 2-AR activation resulted in increases in Na-K-adenosinetriphosphatase (Na-K-ATPase) activity and transcellular sodium transport as a consequence of increased apical sodium entry. The purpose of this study was to determine the role of protein kinase C (PKC) on beta 2-AR-dependent increases in Na-K-ATPase activity and sodium transport in proximal tubules. To determine the effect of PKC on basal function, cultured rat proximal tubule cells were exposed to phorbol 12-myristate 13-acetate (PMA). PMA increased apical Na entry (+/-80%), decreased Na-K-ATPase activity (+/-25%), and prevented increases in Na-K-ATPase activity after sodium entry facilitation with monensin. Decreases in Na-K-ATPase activity were associated with decreases in sodium transport (+/-30%). To determine whether beta 2-AR function was transduced by PKC, PKC activity was measured in cells exposed to the selective beta 2-AR agonist metaproterenol. Metaproterenol caused increases in PKC activity, which were blocked by a beta 2-AR but not by a beta 1-AR-receptor antagonist. beta 2-AR-dependent increases in apical Na entry, Na-K-ATPase activity, and sodium transport were blocked by calphostin C or staurosporine. To determine whether PKC had additional effects on beta 2-AR function, cells were exposed to metaproterenol and PMA. Metaproterenol-induced increases in Na-K-ATPase activity and sodium transport were blocked by PMA. In conclusion, beta 2-AR-mediated increases in Na-K-ATPase activity and sodium flux are transduced by PKC acting through increases in apical Na entry. However, activation of PKC by phorbol esters inhibits beta 2-AR-dependent increases in Na-K-ATPase activity and sodium transport.

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