title: Kinetics of Cl-dependent K influx in human erythrocytes with and without external Na: effect of NEM.
abstract: The majority of the ouabain-insensitive K influx in human erythrocytes is dependent on the presence of Cl. Recent studies have shown that a portion of the Cl-dependent K influx persists in the absence of external Na (Nao). It has been suggested that this Nao-independent component represents (K + Cl) cotransport, whereas the remainder of the Cl-dependent K influx seen on addition of external Na represents (Na + K + 2Cl) cotransport. In the present studies, the kinetics of Cl-dependent K influx were examined in the presence and absence of external Na, by varying external K and external Cl. Our studies suggest that the Nao-independent Cl-dependent pathway has a relatively low affinity for external K (Km 17-30 mM) in contrast to the high affinity of the Nao-augmented component (Km 3-4 mM). N-ethylmaleimide (NEM) stimulates the maximal velocity of the Nao-independent Cl-dependent K influx achievable without alteration of intracellular solutes but does not alter its Km for external K. In contrast, NEM has no stimulatory effect on the Nao-augmented component. The Cl dependence of the Nao-independent K influx is best described by a relatively flat curve with a mild upward concavity. The kinetic properties of the Nao-independent component of Cl-dependent K transport are very similar to those of the putative (K + Cl) cotransport pathway seen in low-K sheep erythrocytes.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D001692:Biological Transport; D002712:Chlorides / Q000502:physiology*; D003470:Culture Media; D004912:Erythrocytes / Q000378:metabolism*; D005033:Ethylmaleimide / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D009566:Nitrates / Q000494:pharmacology; D011188:Potassium / Q000097:blood* / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology*
chemical_list: D002712:Chlorides; D003470:Culture Media; D009566:Nitrates; D012964:Sodium; D005033:Ethylmaleimide; D011188:Potassium