Volume-activated K+(Rb+) efflux in lactating rat mammary tissue

Abstract

The effect of cell swelling, induced by a hyposmotic shock, on K+(Rb+) efflux from lactating rat mammary tissue explants has been studied. A hyposmotic challenge increased the fractional release of K+(Rb+) from mammary tissue in the absence and presence of the loop-diuretic bumetanide (100 μM). However, the volume-sensitive moiety of K+(Rb+) efflux was proportionately larger when bumetanide was present in the incubation medium. On the other hand, a hyposmotic shock appeared to reduce the bumetanide-sensitive component of K+(Rb+) efflux. The increase in K+(Rb+) efflux, induced by cell swelling, was dependent upon the extent of the hyposmotic challenge. In the presence of bumetanide, substituting Cl− with NO3− reduced the initial increase in volume-sensitive K+(Rb+) efflux. However, volume-sensitive K+(Rb+) release was prolonged in the presence of NO3−. Volume-activated K+(Rb+) efflux from rat mammary tissue explants was inhibited by quinine. Cell swelling increased the intracellular concentration of Ca2+ in a fashion which depended on the presence of extracellular Ca2+. However, removing extracellular Ca2+ did not inhibit volume-activated K+(Rb+) efflux from rat mammary tissue explants. The results are consistent with the presence of volume-activated K+ channels in lactating rat mammary tissue. Volume-activated K+ efflux may play a central role in mammary cell volume regulation.