OUABAIN-INDUCED CHANGES IN SODIUM AND POTASSIUM CONTENT AND RESPIRATION OF CEREBRAL CORTEX SLICES: DEPENDENCE ON MEDIUM CALCIUM CONCENTRATION AND EFFECTS OF PROTAMINE

¹ Division of Neurology, University of Washington School of Medicine, Seattle, Washington

The cardiac glycoside ouabain, even while inhibiting the active transport of Na⁺ and K⁺ ions, brings about an increase in respiration of cerebral cortex slices. This effect has now been found to depend upon the presence of Ca⁺⁺ ions in the medium bathing the slice. Slices of guinea-pig cortex incubated in glycyiglycine-buffered media containing 10^-4 M ouabain respired at rates 60% above normal when media contained 2.8 mM CaCl₂ . When Ca⁺⁺ ions were omitted, inhibition of respiration occurred, which reached 70% after 75 min. Decrease in slice content of intracellular K⁺ and increase in intracellular Na⁺ were less marked in Ca⁺⁺-containing media. The respiration increase was also abolished in the presence of the basic polypeptide protamine. Results were interpreted to indicate that Ca⁺⁺ ions and membrane acidic groups help to maintain the physical integrity of the cell membrane structure and thereby prevent ouabain from combining with a portion of the Na⁺ + K⁺-dependent adenosine triphosphatase system. Examination of Ca⁺⁺ binding by cerebral microsomes failed to reveal adenosine triphosphate-dependent uptake of this cation.

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