SODIUM-SELECTIVE CHANNELS IN MEMBRANES OF RAT MACROPHAGES

With the use of the patch-clamp technique, highly selective nonvoltage -gated sodium channels were found in the membrane of rat peritoneal ma crophages. The inward single channel currents were measured in cell-at tached and outside-out mode experiments at different holding membrane potentials within the range of -60 to +40 mV. The channels had a unita ry conductance of 10.2 +/- 0.2 pS with 145 mM Naf in the external solu tion at 23-24 degrees C. The results of ion-substitution experiments c onfirmed that this novel type of cation channel in macrophages is char acterized by high selectivity for Na+ over K+ (as for Cs+, NH4+, Ca2+, Ba2+) ions, whose conduction through these sodium-permeable channels was not measurable. Lithium is the only other ion that is transported by this pathway; the unitary conductance was equal to 3.9 +/- 0.2 pS i n the Li+-containing external solution. Single channel currents and co nductance were found to be linearly dependent on the external sodium c oncentration. Sodium channels in macrophage membrane patches were not blocked by tetrodotoxin(0.01-1 mu M). Single sodium currents were reve rsibly inhibited by the external application of amiloride (0.1-2 mM) a nd its derivative ethylisopropilamiloride (0.01-0.1 mM). The mechanism of channel block by amiloride and its analogue seems to be different.