BACKGROUND: Propofol (2,6-diisopropylphenol) is a widely used intravenous anesthetic, and the effects of propofol on several ion channels have been studied at the whole cell and single-channel levels. However, in general there is no report on the effect of propofol on outward K+ currents in canine colonic myocytes, in which there are two types of outward K+ currents, a large-conductance Ca2+-activated K+ current and a classical delayed rectifier K+ current. We examined the effects of propofol on the two types of outward K+ currents the kinetics involved.

METHODS: Experiments were performed on freshly dispersed smooth muscle cells from the circular muscle layer of the proximal canine colon. Outward currents were recorded using the patch clamp technique in the whole cell configuration.

RESULTS: The application of propofol (600 nM-600microM) decreased net outward current in a dose-dependent manner. Propofol (6-60microM) also decreased peak delayed rectifier K+ currents. Pretreatment with TEA abolished propofol effects on delayed rectifier K+ currents. However, propofol still decreased delayed rectifier K+ currents in the presence of 4-AP.

CONCLUSIONS: These data suggest that propofol decrease net outward K+ currents primarily by inhibiting large-conductance Ca2+-activated K+ currents and 4-AP resistant delayed rectifier K+ currents. These results suggest that propofol action on outward currents may depend on the different blocking mechanisms of the different types of K+ channels. If propofol cannot induce contraction, Ca2+ currents in colonic myocytes warrant further study.