Ransom Christopher B, Liu Xiaojin, Sontheimer Harald
Department of Neurobiology, University of Alabama, Birmingham, Alabama.
Glia. 2002 Jun;38(4):281-91. doi: 10.1002/glia.10064.
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+). 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+) 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.
我们之前已证实在人胶质瘤细胞中存在大电导钙激活钾（BK）通道的表达。在本研究中，我们对切除膜片上胶质瘤BK通道的钙敏感性进行了表征。内面向外膜片中的通道在-60 mV时被2.1×10⁻⁶ M的胞质Ca²⁺激活，具有高度的K⁺选择性，斜率电导约为210 pS。我们通过在具有不同游离[Ca²⁺]i的外面向外膜片中分离BK电流，详细表征了这些通道的Ca²⁺敏感性。在0 Ca²⁺/10 EGTA条件下，外面向外膜片中胶质瘤BK电流的通道激活半最大电压V(0.5)为+138 mV。当游离[Ca²⁺]i分别为1.5×10⁻⁷ M和2.1×10⁻⁶ M时，V(0.5)分别移至+81 mV和-14 mV。这些结果表明，胶质瘤BK通道比许多其他人体标本中描述的具有更高的Ca²⁺敏感性。从在HEK细胞中表达的克隆BK通道（hbr5）获得的数据支持了胶质瘤BK通道对钙具有异常高敏感性的结论。此外，胶质瘤BK通道对BK抑制剂粉防己碱的敏感性表明胶质瘤细胞表达BK通道辅助β亚基。胶质瘤细胞表达BK通道辅助β亚基可能与胶质瘤BK通道的高Ca²⁺敏感性有关。
