期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 107, 期 21, 页码 9897-9902出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1004552107
关键词
cell-cell coupling; pH-dependent gating; EGFP; hemichannel; connexon
资金
- NHLBI NIH HHS [R01 HL084464-04, R01 HL084464, HL084464] Funding Source: Medline
- NINDS NIH HHS [R01 NS045287, R01 NS036706, NS045287, NS036706, R01 NS036706-09] Funding Source: Medline
Intracellular pH (pHi) can change during physiological and pathological conditions causing significant changes of electrical and metabolic cell- cell communication through gap junction (GJ) channels. In HeLa cells expressing wild-type connexin45 (Cx45) as well as Cx45 and Cx43 tagged with EGFP, we examined how pHi affects junctional conductance (g(j)) and g(j) dependence on transjunctional voltage (V-j). To characterize V-j gating, we fit the g(j)-V-j relation using a stochastic four-state model containing one V-j-sensitive gate in each apposed hemichannel (aHC); aHC open probability was a Boltzmann function of the fraction of V-j across it. Using the model, we estimated gating parameters characterizing sensitivity to V-j and number of functional channels. In homotypic Cx45 and heterotypic Cx45/Cx43-EGFP GJs, pH(i) changes from 7.2 to similar to 8.0 shifted g(j)-V-j dependence of Cx45 aHCs along the V-j axis resulting in increased probability of GJ channels being in the fully open state without change in the slope of g(j) dependence on V-j. In contrast, acidification shifted g(j)-V-j dependence in the opposite direction, reducing open probability; acidification also reduced the number of functional channels. Correlation between the number of channels in Cx45-EGFP GJs and maximal gj achieved under alkaline conditions showed that only similar to 4% of channels were functional. The acid dissociation constant (pKa) of g(j)-pH(i) dependence of Cx45/Cx45 GJs was similar to 7. The pK(a) of heterotypic Cx45/Cx43-EGFP GJs was lower, similar to 6.7, between the pK(a)s of Cx45 and Cx43-EGFP (similar to 6.5) homotypic GJs. In summary, pHi significantly modulates junctional conductance of Cx45 by affecting both V-j gating and number of functional channels.
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