Potassium-chloride cotransport in cultured chick heart cells

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Abstract
The polystrand preparation of cultured chick heart cells has a unidirectional transmembrane Cl- efflux that is twice K+ efflux. However, Cl- conductance of this heart cell membrane is low [regardless of extracellular K+ (K+o)], suggesting the existence of electroneutral Cl--dependent transport mechanisms. Furosemide (10(-3) M) decreases the 36Cl tracer efflux rate constant from a control value of 0.67 to 0.33 min-1. Extracellular Na+--free solution, which depletes intracellular Na+ within 1 min, has no significant effect on 36Cl efflux. K+o-free solution plus 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 10(-4) M) promotes the loss of Cl- against the Cl- electrochemical gradient; Cl- loss is furosemide sensitive in a dose-dependent manner. Incubating polystrands in 133 mM K+o, normal extracellular Cl- (Cl-o) solution causes net K+ and Cl- uptake in a 1:1 stoichiometry as well as a furosemide-sensitive volume increase; 130 mM extracellular choline or Li+ cannot mimic this high-K+o-induced volume increase. Removal of Cl-o from 133 mM K+o solution prevents K+ uptake and causes a Cl- loss as well as a furosemide-sensitive volume decrease. Adjusting Cl-o concentrations in high-K+o solution plus DIDS, so that the Cl- chemical gradient equally opposes the K+ chemical gradient, prevents high-K+o-induced volume changes. These data suggest that the cardiac cell membrane contains a furosemide-sensitive K+-Cl- cotransport mechanism.