Parathormone sensitivity and responses to protein kinases in subclones of opossum kidney cells

Parathyroid hormone (PTH) inhibits sodium-dependent phosphate (Na⁺-Pi) transport in the renal proximal tubule and opossum kidney (OK) cells by mechanisms involving protein kinases (PK) A and C, and 20-hydroxyeicosatetraneoic acid (20-HETE). The magnitude of the effect of PKA and PKC on Na⁺-Pi transport in OK cells varies in different studies, suggesting that OK cell subclones are functionally heterogeneous despite their morphological similarity. We studied the effect of PTH and PK effectors in two separate sets of OK cells at two different time periods. Each group of cells were derived from the same stock, at passages 75–85. In one group of OK cells 20-HETE (10⁻⁷ M) induced a 24% decrease in Na-³²Pi transport. Addition of PTH (10⁻⁷ M) inhibited Pi transport by 44%. Addition of TPA (10⁻⁸ M) resulted in a 32% decrease in Na-³²Pi transport. Exposure of cells to the PKC inhibitor staurosporine (10⁻⁷ M) induced a significant increase in Na-³²Pi transport. Simultaneous addition of 20-HETE and staurosporine restored baseline Pi transport. Finally, Br-cAMP (10⁻⁷ M) inhibited Na-³²Pi transport by 32%. In another group of OK cells we reexamined the affect of these substances on Na-³²Pi transport. 20-HETE (10⁻⁷ M) induced a significant increase (30%) in Na-³²Pi transport. PTH (10⁻⁷ M) had no effect on Na-³²Pi transport (P=0.05). TPA (10⁻⁸ M) induced a 42% increase in Na-³²Pi transport (P<0.01). Staurosporine (10⁻⁷ M) induced a slight decrease in Na-³²Pi transport (P<0.05). Simultaneous addition of 20-HETE and staurosporine restored Na-³²Pi transport to baseline levels. Finally, Br-cAMP (10⁻⁷ M) inhibited Na-³²Pi transport by 23%. We conclude that different groups OK cells have markedly different responses to regulators of Na-Pi cotransport.