Arachidonic acid blocks large-conductance chloride channels in L6 myoblasts

Modulation of high-conductance chloride channels by eicosanoids, stilbene derivatives and Zn2+ ions was studied in cultured myoblasts (L6 rat muscle cell line) in excised and cell-attached membrane patches using a conventional patch clamp method. Arachidonic acid (AA) blocked the channel at concentrations 1-50 mumol/l from the internal side of the membrane in excised (inside out) patches with a time constant of about 20 s. The block was absent when arachidonic acid was applied to the bathing solution in cell attached patches, or to the pipette solution, respectively. Arachidonic acid changed the probability of the channel being in the open state (Popen) in dependence on the applied voltage (V). The asymmetric bell-shaped Popen - V relationship showed a steeper dependence on both the negative and positive voltage, respectively, in arachidonic acid solutions. The midpoint potentials (Vh) of the Popen - V relationship were shifted towards lower membrane potential displacements from the holding potential. The recovery from the block was very slow but was found to be enhanced by application of a symmetric voltage ramp pulse. The stilbene derivative (DIDS) blocked the channel at mu molar concentrations (10-100 mumol/l) applied from the internal side of the membrane. The onset and recovery of the DIDS block showed characteristics similar to the AA block. The channel was found to be blocked reversibly by short application of Zn+ ions (1-10 mmol/l) from the internal side of the membrane.