Abstract
1. The effects of histamine, noradrenaline and caffeine were studied in freshly dispersed smooth muscle cells from the rabbit pulmonary artery using the perforated patch technique. 2. In potassium-containing solutions at a holding potential of -50 mV all three agents evoked net inward and outward currents. At 0 mV only an outward current was observed and this response was not produced in potassium-free conditions. 3. In K(+)-free solutions the reversal potential (Er) of the inward current was dependent upon the transmembrane anion gradient but not on the cation gradient. Thus all three agents produced an increase in potassium and chloride conductance. 4. Bath-applied histamine evoked repetitive potassium and chloride currents in many cells. Bath-applied noradrenaline and caffeine, to a lesser extent, also caused repetitive currents but the brief ionophoretic application of noradrenaline never produced oscillations in membrane current. 5. Histamine reduced or abolished the amplitude of spontaneous transient potassium and chloride currents. 6. Histamine-induced currents were blocked by caffeine (10 mM) but could be recorded in Ca(2+)-free bathing solutions. 7. It is concluded that in the rabbit pulmonary artery histamine evokes single and oscillatory membrane potassium and chloride currents which are mediated by the release of calcium from intracellular caffeine-sensitive stores.