Two components of calcium‐activated potassium current in rat adrenal chromaffin cells.

1. The activation of calcium (Ca2+)‐dependent potassium (K+) currents in dissociated rat adrenal chromaffin cells was investigated using the dialysed cell recording technique. 2. Ca(2+)‐dependent K+ current was the major component of outward current at command potentials from ‐30 mV to about +50 mV. 3. Two components of Ca(2+)‐dependent outward current could be distinguished based on the voltage dependence of activation, the properties of tail currents following repolarization, and pharmacological properties. 4. One Ca(2+)‐dependent current was similar to an after‐hyperpolarization current (often termed IAHP) observed in other cell types. This current was largely blocked by 200 nM‐apamin or 200 microM‐curare, was associated with slow Ca(2+)‐dependent tail current, and exhibited little dependence on voltage. In cells with cytosolic Ca2+ buffered to 500 nM‐1 microM, curare‐sensitive current accounted for most of the membrane current at potentials negative to about ‐40 mV. 5. A second component of Ca(2+)‐activated K+ current exhibited voltage‐dependent activation, was completely blocked by 1 mM‐TEA, and turned off rapidly following repolarization. An unusual aspect of the TEA‐sensitive currents was that they appeared to inactivate under conditions of constant cytosolic Ca2+. 6. A novel observation during these experiments was a slow hump of outward current which appears to result from a non‐monotonic elevation in cytosolic Ca2+ during prolonged voltage jumps.