Figure 3. Membrane current response to prolonged application of histamine recorded in voltage-clamp using perforated whole-cell configuration.

The holding potential was −50 mV, with a 1 s hyperpolarizing voltage step to −80 mV applied once every 10 s. Application of histamine caused a pronounced initial outward current that corresponded with the initial membrane hyperpolarization observed in membrane potential records. Note the second outward current in this cell, correlating with the multiple hyperpolarizations noted in other cells. The initial outward current was followed by a maintained inward shift in holding current that correlated with the sustained membrane depolarization. This inward current was associated with an increase in membrane resistance of about 60 %.