ACTIVATION OF MEMBRANE OUTWARD CURRENTS BY HUMAN LOW-DENSITY-LIPOPROTEIN IN MOUSE PERITONEAL-MACROPHAGES

The aim of the present study was to search for electrophysiological effects of human lipoproteins on membrane currents in mouse peritoneal macrophages which had been cultured for 5 to 20 days. Whole-cell currents were recorded by using a voltage-clamp technique. Low density lipoprotein (LDL, 100 mug/ml) increased a slowly activating nonspecific cation current (i(so)) in the positive potential range to 244+/-23% of the reference (test potential + 55 mV, n = 13, P < 0.005). Augmentation of current resulted out of a negative shift of the activation curve along the voltage axis (-22 mV) and an increase of maximally available current. Furthermore, LDL increased a rapidly activating outward current (i(fo)) at test potentials positive to the potassium equilibrium potential. At +55 mV i(fo)-amplitude increased to 165+/-14% of reference (n = 16, P < 0.005). LDL-induced effects on i(fo)-current could be mimicked by application of the calcium ionophore A 23187 (1 mumol/l) which led to an increase of i(fo)-current to 161+/-25% of the reference (test potential +55 mV, n = 11, P < 0.005). Acetylated-LDL (100 mug/ml, 5-15 min) produced no significant effect on the membrane currents under investigation.