We describe here the cloning of the Aplysia K+ channel AK01a.AK01a codes for a protein of 515 amino acids, shows considerable homology to other cloned potassium channels, and can be classified as a member of the ShakerK+ channel family. Expression of the AK01a channel in Xenopus oocytes produces a rapidly inactivating outward potassium current (IAK01a) resembling the A-type currents of Drosophila Shaker. Gating for this current is shifted to potentials considerably more positive than the traditional A-currents of Aplysia; we have, however, identified a novel transient potassium current (IAdepoI) in a subset of Aplysia neurons that has similar gating and pharmacological properties to IAK01a.

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We have cloned an inwardly rectifying K+ channel from the hamster insulinoma cDNA library and shown that it is inhibited by cytoplasmic ATP. The channel is 90.97% identical to the IRK3 channels cloned from other species, and its mRNA is found primarily in the brain. When expressed in Xenopus oocytes, the channel displays strong inward rectification typical of inward rectifiers. The channel is inhibited reversibly by physiological concentrations of ATP via a mechanism that does not appear to involve ATP hydrolysis, as shown by studies of channels in excised inside-out membrane patches. This effect is antagonized by ADP, again in the physiological range, implying that this channel is sensitive to the index of metabolic state, i.e., the intracellular [ATP]/[ADP] ratio. This channel is different from previously known ATP-sensitive K+ channels, although it may also be stimulated by MgATP, as are other ATP-sensitive K+ channels. The potential physiological significance of these ATP-dependent regulations will be discussed.