Kinetic Parameters of Rubidium Transport Pathways Are Normal in Cystic Fibrosis Red Cells

Abstract

ABSTRACT. The abnormalities in ion transport in cystic fibrosis (CF) respiratory and sweat duct epithelia have prompted Studies of ion permeability in CF red blood cells (RBC) although previous reports have been contradictory. In this study, the kinetic characteristics of the three major cation transport systems in RBC were evaluated by measuring rubidium (Rb) uptake at various external Rb concentrations. The maximal velocity and affinity for external Rb (KH) of the NaK pump were normal in CF RBC, as were the maximal velocity and K, for Rb of the NaK cotransport system. Residual (ouabain and bumetanide insensitive) Rb uptake, and steady state RBC Na and K contents were also normal. These data indicate the NaK pump and cotransport system do not exhibit primary or secondary perturbations in CF RBC, and suggest that the noncarrier-mediated membrane permeability to cations is also normal in these cells. (Pediatr Res 24: 495-498, 1988) Abbreviations CF, cystic fibrosis RBC, red blood cell V , , maximal velocity K, Rb, external K or Rb PBS, phosphate-buffered saline OS, ouabain-sensitive Co, cotransport CF is an autosomal recessive disorder manifesting multiple exocrine abnormalities (1). The diagnostically important elevation of sweat chloride reflects malfunctioning of the salt resorbing mechanisms of sweat duct epithelium. Recent work has indicated that the basis of this dysfunction is low C1 permeability of the apical membrane of the ductal epithelial cells (2). Respiratory epithelia share this defect (3), which appears in these cells to arise from abnormalities of the adrenergic regulatory mechanisms of the C1 channel (4-6). Other recent studies of CF respiratory epithelia have also shown increased permeability of the apical membrane to Na, accompanied by elevated Na pump rates at the basolateral membrane, with increased numbers of [3H]ouabain binding sites and ouabain-inhibitable oxygen consumption (7). These findings suggest that, in addition to the C1 channel,