ATP activates a Ca(2+)-dependent Cl- current in the rat thyroid cell line, FRTL-5

Area of Science:

• Cellular electrophysiology
• Purinergic signaling
• Thyroid cell biology

Background:

• Thyroid cells (FRTL-5) exhibit a resting membrane potential sensitive to potassium.
• Extracellular ATP is known to modulate various cellular functions through purinergic receptors.

Purpose of the Study:

• To investigate the effects of external ATP on membrane potential and transmembrane current in FRTL-5 cells.
• To elucidate the signaling pathways and receptor types involved in ATP-induced cellular responses.

Main Methods:

• Patch-clamp whole-cell recording configuration.
• Application of ATP and its analogs, P2 receptor agonists/antagonists.
• Intracellular perfusion with inositol trisphosphate (IP3) and calcium chelation.

Main Results:

• ATP ( > 1 microM) increased chloride conductance, causing membrane depolarization, blocked by quinidine.
• ATP-induced changes were inhibited by intracellular calcium chelation.
• Inositol trisphosphate (IP3) mimicked ATP's effect on chloride current.
• ATP induced a calcium influx pathway, evidenced by a secondary response upon calcium readmission.
• ADP and ATP gamma S mimicked ATP's effects; AMP and adenosine did not.
• Specific P2X and P2Y agonists were ineffective.

Conclusions:

• ATP elicits a significant inositol trisphosphate (IP3)-mediated, calcium-dependent chloride current and membrane depolarization in FRTL-5 cells.
• These effects are mediated through a novel P2-type purinergic receptor.
• The findings reveal a new mechanism of purinergic signaling in thyroid cells.