High Activity of Hemichannels Permeable to Calcium Ions Leads to ROS Generation and Reduced Cell Viability

Area of Science:

• Cell Biology
• Ion Channel Physiology
• Biochemistry

Background:

• Hemichannels (HCs), formed by connexins (Cxs) and pannexin1 (Panx1), facilitate intercellular communication by allowing ion and small molecule exchange.
• Elevated intracellular calcium (Ca2+) and increased HC activity are linked to cell death and pathological conditions.

Purpose of the Study:

• To investigate the role of high hemichannel activity in Ca2+ influx and subsequent cell death.
• To determine if alkaline extracellular conditions (pH 8.5) induce Ca2+ permeability in various HCs.
• To identify novel Ca2+-permeable HCs and elucidate their contribution to alkaline stress-induced cell death.

Main Methods:

• Utilized HeLa cells expressing different connexins (Cx39, Cx43, Cx45) and pannexin1 (Panx1).
• Applied alkaline extracellular solution (pH 8.5) to stimulate hemichannel activity.
• Assessed hemichannel activity using dye uptake assays and measured Ca2+ influx and cell viability.

Main Results:

• Alkaline stress significantly increased hemichannel activity in cells expressing Cx39, Cx43, Cx45, and Panx1, but not in parental cells.
• Connexin 45 (Cx45) hemichannels were identified as novel Ca2+-permeable channels, alongside Cx43.
• Elevated Ca2+ influx through Cx43 and Cx45 HCs under alkaline stress led to increased cytosolic Ca2+, lipid peroxidation, and reduced cell viability.

Conclusions:

• Connexin 45 (Cx45) hemichannels are permeable to Ca2+ and contribute to cell death under alkaline stress.
• Alkaline stress promotes Ca2+ entry via Cx43 and Cx45 hemichannels, inducing oxidative stress and cell death.
• The findings highlight the critical role of specific hemichannels in mediating cellular responses to environmental stress.