Activation of a Ca²⁺‐permeable cation channel by two different inducers of apoptosis in a human prostatic cancer cell line

Abstract

We have combined patch clamp recording with simultaneous [Ca2+]i measurements in single LNCaP cells (a human prostate cancer cell line), to study the activation of Ca2+‐permeable channels by two different inducers of apoptosis, ionomycin and serum deprivation. In perforated patch recording, LNCaP cells had a membrane potential of ‐40 mV and a resting [Ca2+]i of 90 nM. Application of ionomycin at levels that induced apoptosis in these cells (10 μM) produced a biphasic increase in [Ca2+]i. The first rise in [Ca2+]i was due to release of Ca2+ from internal stores and it was associated with a membrane hyperpolarization to ‐77 mV. The latter was probably due to the activation of high conductance, Ca2+‐ and voltage‐dependent K+ channels (maxi‐K). Conversely, the second rise in [Ca2+]i was always preceded by and strictly associated with membrane depolarization and required external Ca2+. Serum deprivation, another inducer of apoptosis, unmasked a voltage‐independent Ca2+ permeability as well. A lower concentration of ionomycin (1 μM) did not induce apoptosis, and neither depolarized LNCaP cells nor produced the biphasic increase in [Ca2+]i. However, the first increment in [Ca2+]i due to release from internal Ca2+ stores was evident at this concentration of ionomycin. Simultaneous recordings of [Ca2+]i and ion channel activity in the cell attached configuration of patch clamp revealed a Ca2+‐permeable, Ca2+‐independent, non‐selective cation channel of 23 pS conductance. This channel was activated only during the second increment in [Ca2+]i induced by ionomycin. The absence of serum activated the 23 pS channel as well, albeit at a lower frequency than with ionomycin. Thus, the 23 pS channel can be activated by two unrelated inducers of apoptosis and it could be another Ca2+ influx mechanism in programmed cell death of LNCaP cells.

Mitochondrial stress-induced calcium signaling, phenotypic changes and invasive behavior in human lung carcinoma A549 cells

“…There is also compelling evidence that Ca 2+ , released through select sources such as the IP3 regulated release, is preferentially taken up by mitochondria, possibly due to proximity of the mitochondrial import sites with the ER release sites (Szalai et al, 1999). In fact, mitochondrial uptake of large amounts of Ca 2+ is thought to be an important factor in apoptosis (Andreyev and Fiskum, 1999;Gutierrez et al, 1999;Stridh et al, 1999;Iwakura et al, 2000). Recent studies show that disruption of Dc m also induces mitochondrial permeability pore transition, a major site of mitochondrial Ca 2+ transport.…”

Evidence that TRPM8 Is an Androgen-Dependent Ca2+ Channel Required for the Survival of Prostate Cancer Cells

“…To test whether the androgen-regulated TRPM8 Ca 2ϩ -permeable channel is coupled with Ca 2ϩ and other signaling pathways involved in cell survival (14,15), LNCaP cells were incubated with capsazepine for 3 days, and nuclear morphology and cell viability then were examined. Cells grown in RPMI plus FCS with 10 mol/L capsazepine exhibited nuclear condensation and fragmentation (Fig.…”

Expression of Drosophila Ca2+ permeable transient receptor potential-like channel protein in a prostate cancer cell line decreases cell survival

“…4,5 There is evidence for a sustained increase in the cytoplasmic free Ca 2+ concentration ([Ca 2+ ] cyt ) in androgen-dependent normal prostate epithelial cells and androgen-dependent prostate cancer cells prior to the onset of apoptosis, and for a decreased apoptotic response when the extracellular Ca 2+ concentration is low. 2,4,5 The failure to initiate this increase in [Ca 2+ ] cyt following androgen ablation is believed to play an important role in the emergence of a hormone refractory phenotype. 6 In animal models, the Ca 2+ channel blocker nifedipine was found to inhibit castration-induced apoptosis and tumor regression.…”