Transmembrane calcium influx induced by ac electric fields.

Area of Science:

• Cell Biology
• Electrophysiology
• Biophysics

Background:

• Exogenous electric fields trigger cellular responses, including alterations in intracellular calcium ion concentration ([Ca2+]i).
• While direct current (DC) electric fields' effects on [Ca2+]i are known, quantitative data on alternating current (AC) electric fields and their mediating calcium pathways are scarce.

Purpose of the Study:

• To quantitatively measure the effects of AC electric fields on intracellular calcium ([Ca2+]i) levels in a model cell system.
• To identify the specific calcium ion pathways involved in AC electric field-induced calcium signaling.

Main Methods:

• Human hepatoma (Hep3B) cells were exposed to 1 or 10 Hz AC electric fields.
• Epifluorescence microscopy was used to monitor changes in intracellular calcium ([Ca2+]i) concentration.
• Experiments involved extracellular calcium depletion and the use of specific inhibitors (U73122, GdCl3, CoCl2).

Main Results:

• A fourfold increase in [Ca2+]i (50 nM to 200 nM) was observed within 30 minutes of AC electric field exposure.
• The increase in [Ca2+]i was dependent on extracellular calcium, indicating influx across the plasma membrane.
• Inhibitors of phospholipase C (U73122) did not affect the calcium increase, ruling out receptor-regulated release.
• GdCl3 (stretch-activated channel inhibitor) and CoCl2 (non-specific calcium channel blocker) partially inhibited the [Ca2+]i increase, with combined treatment causing complete inhibition.

Conclusions:

• AC electric fields induce a significant increase in intracellular calcium ([Ca2+]i) in Hep3B cells primarily through influx from the extracellular environment.
• The calcium influx is mediated by stretch-activated cation channels and non-specific calcium channels.
• Receptor-regulated intracellular calcium release pathways are not involved in AC electric field-induced calcium elevation.