Regulation of the Na, K‐ATPase activity of Madin‐Darby Canine Kidney cells in defined medium by Prostaglandin E1 and 8‐bromocyclic AMP

Abstract

The role of PGE₁ in regulating the activity of the Na⁺, K⁺ ‐ATPase in Madin Darby Canine Kidney (MDCK) cells has been examined. PGE¹ increased the initial rate of ouabain‐sensitive Rb⁺ uptake by MDCK cells, a process that continued to occur over a 5‐day period The increase in the initial rate of ouabain‐sensitive Rb⁺ uptake in MDCK cells treated with PGE¹ could be explained by a 1.6‐fold increase in the V_max for ouabain‐sensitive Rb⁺ uptake. The increase in the V_max for ouabain‐sensitive Rb⁺ uptake observed in MDCK cells under these conditions can be explained either by an increase in the number of active Na⁺ pumps, or by an increase in the efficiency of the Na⁺ pumps. Consistent with the former possibility is the observed increase in the number of ouabain binding sites, as well as the increase in Na⁺, K⁺‐ATPase activity in cell lysates obtained from MDCK monolayers treated with PGE¹. The involvement of cyclic AMP in mediating these effects of PGE¹ on the Na⁺, K⁺‐ATPase in MDCK cells is supported by: (1) the observation of similar effects in 8‐bromocyclic AMP treated MDCK monolayts, and (2) a dramatic reduction of the stimulatory effects of PGE¹ and 8‐bromocyclic AMP on the V_max for ouabain‐sensitive Rb⁺ uptake, and on the number of ouabain binding sites in dibutyryl cyclic AMP resistant clone 3 (DB^r 3) (which is defective in cyclic AMP dependent protein kinase activity). PGE₁ independent MDCK monolayers exhibit both an increase in the V_max for ouabain‐sensitive Rb⁺ uptake and an increase in the number of ouabain binding sites in response to 8‐bromocyclic AMP. Apparently, the cyclic AMP phosphodiesterase defect in these PGE₁ independent cells did not cause cellular cyclic AMP levels to be elevated to a sufficient extent to maximally increase the Na⁺, K⁺‐ATPase activity in these variant cells.