Received for publication September 19, 2008.
Revised November 18, 2008.
Accepted for publication November 19, 2008.

Pharmacological characterization of pannexin-1 currents expressed in mammalian cells

Abstract

Pannexin 1 (Panx1) is a widely expressed protein that shares structural, but not amino acid, homology with gap junction proteins, the connexins. Panx1 does not form gap junctions in mammalian cells but it may function as a plasma membrane hemichannel. Little is known of the pharmacological properties of panx1 expression in mammalian cells. Here we identify three variants in the human PANX1 gene. We expressed these variants and mouse Panx1 in mammalian cells and compared Panx1-induced currents. All human Panx1 variants and the mouse Panx1 showed identical protein expression levels, localization patterns, and functional properties although the frequency of functional expression was species-dependent. Panx1 currents were independent of changes in extracellular or intracellular calcium or phospholipase C transduction. We found compounds that inhibited Panx1 currents with a rank order of potency: CBX > DIDS SITS NPPB > IAA-94 >> probenecid >> FFA = NFA. Triphosphate nucleotides (ATP, GTP and UTP) rapidly and reversibly inhibited Panx1 currents via mechanism(s) independent of purine receptors. When Panx1 was co-expressed with P2X₇R, DIDS was found to act as a P2X₇R antagonist to inhibit ATP-evoked currents, but none of the other compounds inhibited P2X₇R currents. This is the first detailed pharmacological characterization of Panx1 mediated currents in mammalian cells and sheds new, though contradictory, light on the hypothesis that Panx1 acts as a hemichannel to allow passage of large molecules in response to P2X₇R activation.

Key words: P2X7 receptor, heterologous expression, ion channels, pannexins, patch clamp, purine receptors