Pharmacological activation of cloned intermediate- and small-conductance Ca(2+)-activated K(+) channels.
We previously characterized 1-ethyl-2-benzimidazolinone (1-EBIO), as well as the clinically useful benzoxazoles, chlorzoxazone (CZ), and zoxazolamine (ZOX), as pharmacological activators of the intermediate-conductance Ca(2+)-activated K(+) channel, hIK1. The mechanism of activation of hIK1, as well as the highly homologous small-conductance, Ca(2+)-dependent K(+) channel, rSK2, was determined following heterologous expression in Xenopus oocytes using two-electrode voltage clamp (TEVC) and excised, inside-out patch-clamp techniques. 1-EBIO, CZ, and ZOX activated both hIK1 and rSK2 in TEVC and excised inside-out patch-clamp experiments. In excised, inside-out patches, 1-EBIO and CZ induced a concentration-dependent activation of hIK1, with half-maximal (K(1/2)) values of 84 microM and 98 microM, respectively. Similarly, CZ activated rSK2 with a K(1/2) of 87 microM. In the absence of CZ, the Ca(2+)-dependent activation of hIK1 was best fit with a K(1/2) of 700 nM and a Hill coefficient (n) of 2.0. rSK2 was activated by Ca(2+) with a K(1/2) of 700 nM and an n of 2.5. Addition of CZ had no effect on either the K(1/2) or n for Ca(2+)-dependent activation of either hIK1 or rSK2. Rather, CZ increased channel activity at all Ca(2+) concentrations (V(max)). Event-duration analysis revealed hIK1 was minimally described by two open and three closed times. Activation by 1-EBIO had no effect on tau(o1), tau(o2), or tau(c1), whereas tau(c2) and tau(c3) were reduced from 9.0 and 92.6 ms to 5.0 and 44.1 ms, respectively. In conclusion, we define 1-EBIO, CZ, and ZOX as the first known activators of hIK1 and rSK2. Openers of IK and SK channels may be therapeutically beneficial in cystic fibrosis and vascular diseases.
Syme
C A
CA
Department of Cell Biology and Physiology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
Gerlach
A C
AC
Singh
A K
AK
Devor
D C
DC
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002753:Chlorzoxazone / Q000494:pharmacology; D005260:Female; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000187:drug effects / Q000378:metabolism; D014982:Xenopus laevis; D015049:Zoxazolamine / Q000494:pharmacology
D001562:Benzimidazoles; D002120:Calcium Channel Agonists; D015221:Potassium Channels; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; D015049:Zoxazolamine; D002753:Chlorzoxazone; C102635:1-ethyl-2-benzimidazolinone