BK channels in human glioma cells have enhanced calcium sensitivity.
We have previously demonstrated the expression of large-conductance, calcium-activated potassium (BK) channels in human glioma cells. In the present study, we characterized the calcium sensitivity of glioma BK channels in excised membrane patches. Channels in inside-out patches were activated at -60 mV by 2.1 x 10(-6) M cytosolic Ca(2+), were highly K(+)-selective, and had a slope conductance of approximately iqual 210 pS. We characterized the Ca(2+) sensitivity of these channels in detail by isolating BK currents in outside-out patches with different free [Ca(2+)](i). The half-maximal voltage for channel activation, V(0.5), of glioma BK currents in outside-out patches was +138 mV with 0 Ca(2+)/10 EGTA. V(0.5) was shifted to +81 mV and -14 mV with free [Ca(2+)](i) of 1.5 x 10(-7) M and 2.1 x 10(-6) M, respectively. These results suggest that glioma BK channels have a higher Ca(2+) sensitivity than that described in many other human preparations. Data obtained from a cloned BK channel (hbr5) expressed in HEK cells support the conclusion that glioma BK channels have an unusually high sensitivity to calcium. In addition, the sensitivity of glioma BK channels to the BK inhibitor tetrandrine suggests the expression of BK channel auxiliary beta-subunits by glioma cells. Expression of the auxiliary beta-subunit of BK channels by glioma cells may relate to the high Ca(2+) sensitivity of glioma BK channels.
Ransom
Christopher B
CB
Department of Neurobiology, University of Alabama, Birmingham, Alabama.
Liu
Xiaojin
X
Sontheimer
Harald
H
D000470:Alkaloids / Q000494:pharmacology; D044182:Benzylisoquinolines; D001932:Brain Neoplasms / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002999:Clone Cells / Q000187:drug effects / Q000378:metabolism; D005910:Glioma / Q000378:metabolism*; D006801:Humans; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D019789:Tetraethylammonium / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D000470:Alkaloids; D044182:Benzylisoquinolines; D002121:Calcium Channel Blockers; D026902:Potassium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; C009438:tetrandrine; D019789:Tetraethylammonium; D011189:Potassium Chloride; D002118:Calcium