Mutations in GJA5 encoding the
gap junction protein connexin40 (Cx40) have been linked to lone
atrial fibrillation. Some of these mutants result in impaired gap junction function due to either abnormal
connexin localization or impaired gap junction channels, which may play a role in promoting
atrial fibrillation. However, the effects of the
atrial fibrillation-linked Cx40 mutants on hemichannel function have not been studied. Here we investigated two
atrial fibrillation-linked germline Cx40 mutants, V85I and L221I. These two mutants formed putative gap junction plaques at cell-cell interfaces, with similar gap junction coupling conductance as that of wild-type Cx40.
Connexin deficient HeLa cells expressing either one of these two mutants displayed prominent
propidium iodide-uptake distinct from cells expressing wild-type Cx40 or other
atrial fibrillation-linked Cx40 mutants, I75F, L229M, and Q49X.
Propidium iodide-uptake was sensitive to [Ca2+]o and the hemichannel blockers,
carbenoxolone,
flufenamic acid and
mefloquine, but was not affected by the pannexin 1 channel blocking agent,
probenecid, indicating that uptake is most likely mediated via
connexin hemichannels. A gain-of-hemichannel function in these two
atrial fibrillation-linked Cx40 mutants may provide a novel mechanism underlying the etiology of
atrial fibrillation.