Abstract

Kir2.0 channels play a significant role in setting the resting membrane potential, modulating action potential wave form, and buffering extracellular potassium. One member of this family, Kir2.3, is highly expressed in the heart and brain and is modulated by a variety of factors, including arachidonic acid (AA). Using two-electrode voltage clamp and inside-out patch clamp recordings from Xenopus laevis oocytes expressing Kir2.3 channels, we found that AA selectively activated Kir2.3 channels with an EC₅₀ of 0.59 μM and that this activation required phosphatidyl inositol 4,5-bisphosphate (PIP₂). We found that AA activated Kir2.3 by enhancing channel-PIP₂ interactions as demonstrated by a shift in PIP₂ activation curve. EC₅₀ for channel activation by PIP₂ were 36 and 12 μM in the absence and presence of AA, respectively. A single point mutation on the channel C terminus that enhanced basal channel-PIP₂ interactions reduced the sensitivity of the channel to AA. Effects of AA are mediated through cytoplasmic sites on the channel by increasing the open probability, mainly due to more frequent bursts of opening in the presence of PIP₂. Therefore, enhanced interaction with PIP₂ is the molecular mechanism for Kir2.3 channel activation by AA.