Erythrocyte sodium-lithium countertransport activity is related to membrane fluidity in IDDM patients

Abstract

Sodium-lithium countertransport (SLC) activity at a standard physiological sodium concentration is raised in uncomplicated IDDM, for which the kinetic mechanism is a raised maximum velocity (Vmax). Diabetic patients with nephropathy do not have raised values for Vmax but a low Michaelis constant (km). Transporter activity could be influenced by its membrane lipid environment. This was assessed in 21 control subjects, 32 uncomplicated diabetic patients, 17 patients with diabetic nephropathy and 11 patients with non-diabetic nephropathy by measuring the fluorescence anisotropy of DPH and TMA-DPH to assess different membrane regions. Standard SLC was higher in all the patient groups compared to the control subjects: 0.307 +/- 0.020 mmol Li/h x 1 cells in uncomplicated IDDM; 0.300 +/- 0.032 in diabetic nephropathy patients and 0.276 +/- 0.019 in non-diabetic nephropathy patients vs 0.216 +/- 0.011 mmol Li/h x 1 cells in control subjects (p < 0.001, p < 0.05, p < 0.05, respectively). This was due to raised Vmax values in the uncomplicated group: 0.528 +/- 0.035 vs 0.385 +/- 0.022 mmol Li/h x 1 cells in control subjects (p = 0.001) and low values for km in the diabetic nephropathy group: 58 (27-170) vs 106 (81-161) mmol/l in control subjects (p < 0.001). Raised SLC in the non-diabetic nephropathy group was largely due to raised Vmax: 0.460 +/- 0.030 mmol Li/h x 1 cells; p = 0.053, with no difference in km: 99.5 (74-137).(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal thiol group modulation of sodium– lithium countertransport and membrane fluidity is associated with a disturbed relationship between serum triacylglycerols and membrane function in Type II diabetes

“…This relationship between the effects of thiol alkylation on membrane fluidity and abnormal Na-Li CT kinetics is, in fact, identical to that described in Type I diabetic subjects with diabetic nephropathy [5,10]. This is not unexpected, since Na-Li CT, membrane fluidity and membrane\ cytoskeletal proteins appear to be functionally interlinked [5,8,10,14].…”

“…This was measured as described in previous reports [8,10]. Briefly, erythrocytes were washed and fluorescence anisotropy was measured in 3 ml aliquots of a 0.1 % packed cell volume suspension of intact erythrocytes in PBS after incubation with a 2 µmol\l solution of trimethylammonium diphenylhexatriene (TMA-DPH) at 37 mC for 5 min.…”

“…It may, however, reflect a generalized cell membrane or cytoskeletal defect, since Na-Li CT is related to membrane fluidity [8]. Both are modified by alkylation of thiol proteins [5,9,10] associated with the membrane\cytoskeleton, and these responses are abnormal in subjects with nephropathy in Type I diabetes [5,10].…”

Sodium–lithium countertransport is increased in normoalbuminuric type 1 diabetes but is not related to other risk factors for microangiopathy

“…However, the data on Na/Li CT activity in diabetic patients are rather confusing. Most investigators report an increased Na/Li CT activity in diabetes [9–12]. This increase may result from either an increased maximal velocity ( V max ), an increased sodium affinity (lower K m ), or both [13].…”

Relevance of erythrocyte Na+/Li+ countertransport measurement in essential hypertension, hyperlipidaemia and diabetic nephropathy: a critical review

“…Thus, the exchange measured as a difference between efflux in Na þ -free and 150 mmol L -1 Na þ -containing medium (V 150 ) seemed also appropriate because 150 mmol L -1 is six times the K 0·5 for Na þ . If, however, the presently available data on kinetics of Na þ /Li þ CT of healthy individuals are analysed (Table 1), it appears that 45 19 0·21 0·39 137 46 15 0·20 0·41 140 74 10 0·25 0·54 137 75 21 0·22 0·39 106 76 22 0·26 0·54 137 99 16 0·17 0·32 132 17 27 0·17 0·48 144 50 10 0·21 0·32 86 16 12 0·19 † 0·30 92 100 16 0·24 0·44 115 101 16 0·24 † 0·36 77 18 25 0·25 0·31 30 64 15 0·20 0·39 91 44 21 0·22 0·40 60 102 22 0·29 0·42 68 103 10 0·26 † 0·41 87…”