O. Ortizcarranza et al., 2 OPERATIONAL MODES OF K-CL COTRANSPORT IN LOW K-BLOOD-CELLS( SHEEP RED), Cellular physiology and biochemistry, 7(5), 1997, pp. 251-263
The present study further characterizes the two operational modes of K
-Cl cotransport in low K+ sheep red blood cells previously described a
nd proposed by us: (i) a membrane-bound cotransport entity devoid of m
odulation by putative kinases/phosphatases, and (ii) an ATP-and Mg-mod
ulated activity. We now report that quinine, spermine, and 300 mu M Ca
-i(2+) inhibit (40-100%) K-Cl efflux in ATP-and Mg-i(2+) depleted cell
s and hence interact directly with the cotransporter moiety. The sensi
tivity of K-Cl cotransport to calyculin, however, was modulated by the
ATP content of the cells: after depletion of both ATP and Mg-i(2+) th
e flux was insensitive to the inhibitor, whereas at about 120 mu mol A
TP/L cells calyculine inhibited K-Cl efflux by 95-100% in Mg-i(2+)-fre
e cells. The K-Cl cotransporter itself, free of modulation by kinases/
phosphatases, 'senses' changes in cell volume perhaps at the membrane/
cytoskeleton level. Cellular ATP then switches the cotransporter's ope
rational mode so that under physiological conditions the rate of K-Cl
efflux is under the control of a putative kinases/phosphatases pathway
.