The Inhibition by Oxaliplatin, a Platinum-Based Anti-Neoplastic Agent, of the Activity of Intermediate-Conductance Ca2+-Activated K+ Channels in Human Glioma Cells

Abstract

Oxaliplatin (OXAL) is a third-generation organoplatinum which is effective against advanced cancer cells including glioma cells. How this agent and other related compounds interacts with ion channels in glioma cells is poorly understood. OXAL (100 µM) suppressed the amplitude of whole-cell K⁺ currents (I_K); and, either DCEBIO or ionomycin significantly reversed OXAL-mediated inhibition of I_K in human 13-06-MG glioma cells. In OXAL-treated cells, TRAM-34 did not suppress I_K amplitude in these cells. The intermediate-conductance Ca²⁺-activated K⁺ (IK_Ca) channels subject to activation by DCEBIO and to inhibition by TRAM-34 or clotrimazole were functionally expressed in these cells. Unlike cisplatin, OXAL decreased the probability of IK_Ca-channel openings in a concentration-dependent manner with an IC₅₀ value of 67 µM. No significant change in single-channel conductance of IK_Ca channels in the presence of OXAL was demonstrated. Neither large-conductance Ca²⁺-activated K⁺ channels nor inwardly rectifying K⁺ currents in these cells were affected in the presence of OXAL. OXAL also suppressed the proliferation and migration of 13-06-MG cells in a concentration- and time-dependent manner. OXAL reduced IK_Ca-channel activity in LoVo colorectal cancer cells. Taken together, the inhibition by OXAL of IK_Ca channels would conceivably be an important mechanism through which it acts on the functional activities of glioma cells occurring in vivo.

Evidence for the Inhibition by Temozolomide, an Imidazotetrazine Family Alkylator, of Intermediate-Conductance Ca2+-Activated K+ Channels in Glioma Cells

“…The single-channel conductance of IK Ca channels in U373 cells was calculated to be 32 pS, a value similar to the prototypical IK Ca channels present in other types of cells [10,11,13,26], but apparently less than that of BK Ca channels [9,27]. Moreover, clotrimazole and TRAM-34 inhibited, but chlorzoxazone and 1-EBIO stimulated the activity of these channels in U373 cells.…”

“…To determine whether the inhibitory effect of TMZ on I K in U373 cells can be shared by the regulators of IK Ca channels, the effects of clotrimazole, TRAM-34, and TRAM-34 plus ionomycin were also investigated. Clotrimazole and TRAM-34 are potent inhibitors of IK Ca channels, whereas ionomycin is a Ca 2+ ionophore [10,12,13]. At −100 mV, the I K amplitude …”

Stimulatory actions of a novel thiourea derivative on large‐conductance, calcium‐activated potassium channels

“…No notable difference in single‐channel conductance of BK Ca channels was demonstrated (189 ± 11 pS [control] vs. 193 ± 12 pS [30 μM compound #326], n = 11, p > 0.05). However, the activity of IK Ca channels in these cells (Huang et al, ; Yeh et al, ) was not subject to stimulation by compound #326 (30 μM). Similar to the observations made earlier, compound #326 at a concentration of 30 μM was effective at stimulating BK Ca channels found in glioma cells.…”

“…Because I K(Ca) present in GH 3 cells may be different from that in other types of cells, the effect of compound #326 in 13‐06‐MG glioma cells was also examined. Previous observations in our laboratory have demonstrated that these glioma cells express BK Ca channels that are sensitive to inhibition by paxilline, another indole diterpene structurally similar to verruculogen (Huang et al, ). Therefore, in a final set of experiments, we investigated effects of this compound on the activity of single BK Ca channels in 13‐06‐MG glioma cells.…”

“…The glioblastoma multiforme cell line (13‐06‐MG) was originally derived from Prof. Dr. Carol A. Kruse, Department of Neurosurgery, Ronald Reagan UCLA Medical Center, LA. Cells were routinely grown at a density of 10 6 /ml in high‐glucose (4 g/L) Dulbecco's modified Eagle media (Invitrogen) supplemented with 10% heat‐inactivated fetal bovine serum, 100 U/ml penicillin and 10 μg/ml streptomycin (Huang, Huang, & Wu, ). The culture medium was changed every 2–3 days for removal of non‐adhering cells, and cells underwent passaged as they reached confluence.…”