Abstract
Ion channels in the plasma membrane are important for the apoptotic process. Different types of voltage-gated ion channels are up-regulated early in the apoptotic process and block of these channels prevents or delays apoptosis. In the present investigation we examined whether ion channels are up-regulated in oocytes from the frog Xenopus laevis during apoptosis. The two-electrode voltage-clamp technique was used to record endogenous ion currents in the oocytes. During staurosporine-induced apoptosis a voltage-dependent Na+ current increased three-fold. This current was activated at voltages more positive than 0 mV (midpoint of the open-probability curve was +55 mV) and showed almost no sign of inactivation during a 1-s pulse. The current was resistant to the Na+-channel blockers tetrodotoxin (1 µM) and amiloride (10 µM), while the Ca2+-channel blocker verapamil (50 µM) in the bath solution completely blocked the current. The intracellular Na+ concentration increased in staurosporine-treated oocytes, but could be prevented by replacing extracellular Na+ whith either K+ or Choline+. Prevention of this influx of Na+ also prevented the STS-induced up-regulation of the caspase-3 activity, suggesting that the intracellular Na+ increase is required to induce apoptosis. Taken together, we have found that a voltage dependent Na+ channel is up-regulated during apoptosis and that influx of Na+ is a crucial step in the apoptotic process in Xenopus oocytes.
Highlights
Programmed cell death, apoptosis, is an essential process in the development and the sculpturing of the growing organism
In the present investigation we have found that an endogenous Na+ channel in Xenopus oocytes is up-regulated during STSinduced apoptosis and that the Na+ influx is essential for the apoptotic process
The described ion channel activated during apoptosis is an atypical Na+ channel
Summary
Programmed cell death, apoptosis, is an essential process in the development and the sculpturing of the growing organism. A number of ion channels open during the early steps of the apoptotic process and block of the channels prevents or delays the apoptotic process. Apoptotic stimuli, such as staurosporine (STS) or serum deprivation has been shown to activate K+ channels [4]. Opening of K+ channels leads to an efflux of K+ ions and a decrease in the intracellular K+ concentration [4,5,6,7]. Opening of Cl2 channels is possibly an essential step in combination with opening of K+ channels [4,15,18] Block of these Cl2 channels has been shown to prevent apoptosis
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