PHARMACOLOGICAL PROPERTIES OF CA2-ACTIVATED K+ CURRENTS OF RAMIFIED MURINE BRAIN MACROPHAGES()

Using the whole-cell configuration of the patch clamp technique, calci um-activated potassium currents (I-K,I-Ca) were investigated in ramifi ed murine brain macrophages. In order to induce I-K,I-Ca the intracell ular concentration of nominal free Ca2+ was adjusted to 1 mu M. The Ca 2+-activated K+ current of brain macrophages did not show any Voltage dependence at test potentials between -120 and +30 mV. A tenfold chang e in extracellular K+ concentration shifted the reversal potential of I-K,I-Ca by 51 mV. The bee venom toxin apamin applied at concentration s of up to 1 mu M did not affect I-K,I-Ca Ca2+-activated K+ currents o f ramified brain macrophages were highly sensitive to extracellularly applied charybdotoxin (CTX). The half-maximal effective concentration of CTX was calculated to be 4.3 nM. In contrast to CTX, the scorpion t oxin kaliotoxin did not inhibit I-K,I-Ca at concentrations between 1 a nd 50 nM. Tetraethylammonium (TEA) blocked 8.0% of I-K,I-Ca at a conce ntration of 1 mM, whereas 31.4% of current was blocked by 10 mM TEA. S everal inorganic polyvalent cations were tested at a concentration of 2 mM for their ability to block I-K,I-Ca La3+ reduced I-K,I-Ca by 72.8 %, whereas Cd2+ decreased I-K,I-Ca by 17.4%; in contrast, Ni2+ did not have any effect on I-K,I-Ca. Ba2+ applied at a concentration of 1 mM reduced I-K,I-Ca voltage-dependently at hyperpolarizing potentials.