Arecoline inhibits intermediate-conductance calcium-activated potassium channels in human glioblastoma cell lines

Arecoline (ARE) is an alkaloid-type natural product from areca nut. This compound has numerous pharmacological and toxicological effects. Whether this agent interacts with ion channels to perturb functional activity of cells remains unknown. The effects of ARE on ionic currents were studied in glioma cell lines (U373 and U87MG) using patch-clamp technique. Like TRAM-34(1-[(2-chlorophenyl)-diphenylmethyl]pyrazole), ARE suppressed the amplitude of whole-cell voltage-gated K⁺ currents in U373 cells elicited by a ramp voltage clamp. In cell-attached configuration, ARE did not modify the single-channel conductance of intermediate-conductance Ca²⁺-activated K⁺ (IK_Ca) channels; however, it did reduce channel activity. Its inhibition of IK_Ca channels was accompanied by a significant lengthening in the slow component of mean closed time of IK_Ca channels. Based on minimal kinetic scheme, the dissociation constant (K_D) required for ARE-mediated prolongation of mean closed time was 11.2 μM. ARE-induced inhibition of IK_Ca channels was voltage-dependent. Inability of ARE to perturb the activity of large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels was seen. Under current-clamp recordings, ARE depolarized the membrane of U373 cells and DCEBIO reversed ARE-induced depolarization. Similarly, ARE suppressed IK_Ca-channel activities in oral keratinocytes. This study provides the evidence that ARE block IK_Ca channels in a concentration, voltage and state-dependent manner. ARE-induced block of IK_Ca channels is unrelated to the binding of muscarinic receptors. The effects of ARE on these channels may partially be responsible for the underlying cellular mechanisms by which it influences the functional activities of glioma cells or oral keratinocytes, if similar findings occur in vivo.