Characterization of the cloned human intermediate-conductance Ca²⁺-activated K⁺ channel

Abstract

The human intermediate-conductance, Ca2+-activated K+ channel (hIK) was identified by searching the expressed sequence tag database. hIK was found to be identical to two recently cloned K+ channels, hSK4 and hIK1. RNA dot blot analysis showed a widespread tissue expression, with the highest levels in salivary gland, placenta, trachea, and lung. With use of fluorescent in situ hybridization and radiation hybrid mapping, hIK mapped to chromosome 19q13.2 in the same region as the disease Diamond-Blackfan anemia. Stable expression of hIK in HEK-293 cells revealed single Ca2+-activated K+ channels exhibiting weak inward rectification (30 and 11 pS at −100 and +100 mV, respectively). Whole cell recordings showed a noninactivating, inwardly rectifying K+ conductance. Ionic selectivity estimated from bi-ionic reversal potentials gave the permeability ( P K/ P X) sequence K+ = Rb+ (1.0) > Cs+ (10.4) ≫ Na+, Li+, N-methyl-d-glucamine (>51).[Formula: see text] blocked the channel completely. hIK was blocked by the classical inhibitors of the Gardos channel charybdotoxin (IC50 28 nM) and clotrimazole (IC50 153 nM) as well as by nitrendipine (IC50 27 nM), Stichodactyla toxin (IC50 291 nM), margatoxin (IC50 459 nM), miconazole (IC50 785 nM), econazole (IC50 2.4 μM), and cetiedil (IC50 79 μM). Finally, 1-ethyl-2-benzimidazolinone, an opener of the T84 cell IK channel, activated hIK with an EC50 of 74 μM.

Opposing effects of spinal nerve ligation on calcium-activated potassium currents in axotomized and adjacent mammalian primary afferent neurons

“…Although others have raised uncertainty about the presence of IK channels in DRG neurons [42,44,77,78], our identification of a clotrimazole-sensitive current suggests that a component of I K(Ca) in these neurons is IK. Other prior observations also support our finding of BK currents in DRG somata [83,102].…”

Role of the NH2 Terminus in the Assembly and Trafficking of the Intermediate Conductance Ca2+-activated K+ Channel hIK1

“…We have demonstrated that IK and SK channels are activated by benzimidazolinones, including 1-ethyl-2-benzimdazolinone and DCEBIO, as well as the centrally acting muscle relaxants chlorzoxazone and zoxazolamine (5,16). We (17) and others (2,3) have demonstrated that clotrimazole is an inhibitor of IK channels. Recently Chandy and colleagues (18) mapped the molecular binding site for this blocker to the pore of hIK1.…”

“…While the IK1 and SK channels share roughly 40% homology, their expression patterns and pharmacology are widely disparate, consistent with their unique physiological functions (1). The human IK1 channel (hIK1) is widely expressed, being found in salivary gland, colon, bladder, stomach, lung, smooth muscle, red blood cells, T-cells, and placenta (2,3) where it plays a crucial role in a variety of physiological functions. Indeed hIK1 plays a seminal role in modulating Ca 2ϩ -dependent transepithelial ion transport (4,5), has recently been confirmed to be the Gardos channel of red blood cells (6), and has been proposed to play a role in both vascular remodeling (7) and in modulating vascular tone (8).…”

Ca2+-activated K+ Channels in Human Leukemic Jurkat T Cells

“…The predominant KCa channel found in normal human peripheral T cells has a 15-40 pS unitary conductance, is a charybdotoxin (CTX)-sensitive and apamin-insensitive inwardly-rectifying channel that is also known as intermediate conductance (IK) (23,24). A gene encoding IK, called hSK4 (or hIK1, hIKCa1, and hKCa4) has been recently cloned from various human tissues (25)(26)(27)(28). The prominent KCa channel expressed in the human leukemic Jurkat T cell line corresponds to an apamin-sensitive, small-conductance channel (4 -7 pS) (16,17).…”