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

摘要

class="enumerated" style="list-style-type:decimal">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.