EVIDENCE FOR FUROSEMID E-SENSITIVE Na⁺-K⁺-Cl^- CO-TRANSPORT IN LACTATING RAT MAMMARY TISSUE

¹ Hannah Research Institute, Ayr, Scotland KA6 5HL

The transport of K⁺ (using ⁸⁶Rb as tracer) by lactating rat mammary tissue slices has been studied in order to seek evidence for Na⁺-K⁺-Cl^- co-transport. Potassium transport was inhibited by furosemide; the locus of inhibition was at a site other than the Na⁺:K⁺ pump. Replacing medium Cl^- with NO₃ reduced the bidirectional movement of K⁺; moreover, furosemide was without effect in a Cl^--free medium. Sodium replacement by N-methyl-D-glucamine acted to reduce the loop diuretic-sensitive component of K⁺ uptake whilst concomitantly increasing K⁺ influx via an ouabain-and furosemide-resistant pathway. Potassium efflux was found to be transiently stimulated by Na⁺ ions; this was attenuated by furosemide. Potassium egress was markedly increased via a furosemide-insensitive pathway when salicylate was used to replace Cl^-. The results are consistent with furosemide-sensitive Na⁺-K⁺-Cl^-co-transport.

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