Pharmacological properties of Ca2+-activated K+ currents of ramified murine brain macrophages.
Using the whole-cell configuration of the patch clamp technique, calcium-activated potassium currents (I(K,Ca)) were investigated in ramified murine brain macrophages. In order to induce I(K,Ca) the intracellular concentration of nominal free Ca2+ was adjusted to 1 microM. The Ca2+-activated K+ current of brain macrophages did not show any voltage dependence at test potentials between -120 and +30 mV. A tenfold change in extracellular K+ concentration shifted the reversal potential of I(K,Ca) by 51 mV. The bee venom toxin apamin applied at concentrations of up to 1 microM did not affect I(K,Ca). Ca2+-activated K+ currents of 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 toxin kaliotoxin did not inhibit I(K,Ca) at concentrations between 1 and 50 nM. Tetraethylammonium (TEA) blocked 8.0% of I(K,Ca) at a concentration of 1 mM, whereas 31.4% of current was blocked by 10 mM TEA. Several inorganic polyvalent cations were tested at a concentration of 2 mM for their ability to block I(K,Ca). La3+ reduced I(K,Ca) by 72.8%, whereas Cd2+ decreased I(K,Ca) by 17.4%; in contrast, Ni2+ did not have any effect on I(K,Ca). Ba2+ applied at a concentration of 1 mM reduced I(K,Ca) voltage-dependently at hyperpolarizing potentials.
Eder
C
C
Abteilung Neurophysiologie, Institut für Physiologie der Charité, Humboldt Universität, Berlin, Germany.
Klee
R
R
Heinemann
U
U
D000818:Animals; D001030:Apamin / Q000494:pharmacology; D001464:Barium / Q000494:pharmacology; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology*; D018999:Charybdotoxin / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D009532:Nickel / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000187:drug effects* / Q000378:metabolism
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D018999:Charybdotoxin; D001030:Apamin; D001464:Barium; D009532:Nickel; D002118:Calcium