Local anesthetic heptacaine inhibited potassium channel from tracheal microsomes

Single channel properties of potassium channels from microsomal membranes i solated from bovine trachea were studied in bilayer lipid membrane (BLM). A fter incorporation of tracheal microsomal membranes into BLM, single channe ls permeable for potassium were observed. Conductance of the channel, at 80 0 mmol/L KCl (or 1.2 mol/L KCl) and 200 nmol/L Ca2+ in the cis side versus 50 mmol/L KCl and 53 mmol/L Ca(OH)(2) in the trans side, was 187 pS (or 234 pS). Its open probability (P-open) varied and was in the range of 0.55-0.8 7. Heptacaine (100 mu mol/L) decreased the open probability of the potassiu m channel from 0.59 to 0.20. Further increase in heptacaine concentrations to 300 mu mol/L decreased P-open to 0.17. At 800 mu mol/L heptacaine concen tration the channel was blocked and a noisy, nonregular current through BLM was induced. We suppose that the inhibitory effect of heptacaine is a resu lt of direct drug-channel interaction and that its induction of non-regular current is a result of drug nonspecific membrane perturbation.