INHIBITION OF NA(-INFECTED CHICK-CELLS()K(+)ATPASE ACTIVITY IN MEMBRANES OF SINDBIS VIRUS)

Alterations in intracellular concentrations of Na+ and K+ in Sindbis v irus-infected cells result largely from inhibition of ouabain-sensitiv e Na(+)K(+)ATPase (Na+ pump) activity. Here we report that membrane pr eparations derived from Sindbis virus-infected chick cells exhibit red uced Na(+)K(+)ATPase activity, indicating that limitation of cellular factors is not responsible for inhibition of ion transport. In vitro p hosphorylation of the Na(+)K(+)ATPase by [P-32]orthophosphate or [gamm a-P-32]ATP is unaltered in membranes of Sindbis virus-infected cells, indicating that a loss of specific enzymatic functions unrelated to fo rmation of Na+ pump phosphoenzyme intermediates occurs during the cour se of viral infection. However, phosphoenzyme intermediates of the Na( +)K(+)ATPase prepared from membranes of Sindbis virus-infected cells a re inherently less stable than those prepared with membranes of uninfe cted cells. The instability of these intermediates in vitro is correla ted with an altered capacity of the Na+ pump to transport monovalent c ations into virus-infected cells. Na-22(+) transport studies reveal en hanced ouabain-sensitive Na+ uptake by Sindbis virus-infected cells, s uggesting that the Na+ pump may catalyze enhanced Na+-Na+ exchange in the infected cells. These results indicate that the capacity of the Na (+)K(+)ATPase to discriminate between binding of extracellular Na+ and K+ is specifically altered during the course of infection by Sindbis virus. (C) 1996 Academic Press, Inc.