Hemichannels in cardiomyocytes open transiently during ischemia and contribute to reperfusion injury following brief ischemia.
The aim of this study was to investigate changes in hemichannel activity during in vitro simulated ischemia [oxygen-glucose deprivation (OGD)] and the contribution of hemichannels to ischemia-reperfusion injury in rat neonatal cardiomyocytes. Dye uptake assays showed that hemichannels opened as OGD progressed, peaking after 1 h, and then closed, returning to the pre-OGD state after 2 h of OGD. The increase in dye uptake after 1 h of OGD was inhibited by hemichannel blockers (lanthanum chloride and a connexin 43 mimetic peptide, Gap26). During OGD, intracellular Ca(2+) concentration ([Ca(2+)](i)) began to increase after 1 h and reached several micromolar after 2 h. After 1 h of OGD, Gap26 inhibited the increases in hemichannel activity and [Ca(2+)](i). In contrast, dantrolene [an endo(sarco)plasmic reticulum Ca(2+) release inhibitor] suppressed the increase in [Ca(2+)](i), but not in hemichannel activity. After 2 h of OGD, the combined administration of 2',4'-dichlorobenzamil and dantrolene reduced [Ca(2+)](i) to <1 microM and increased hemichannel activity to the level attained after 1 h of OGD. Simulated ischemia-reperfusion, induced by 1 h of OGD followed by 2 h of recovery, reduced cell viability to 54% of the control level. The addition of Gap26 to OGD medium improved viability to 80% of the control level. In conclusion, this study demonstrated that 1) hemichannels open transiently during OGD, 2) closure of hemichannels, but not their opening, is regulated by an increase in [Ca(2+)](i) during OGD, and 3) open hemichannels contribute to cell injury during recovery from OGD.
Shintani-Ishida
Kaori
K
Department of Forensic Medicine, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. kaori@m.u-tokyo.ac.jp
Uemura
Koichi
K
Yoshida
Ken-ichi
K
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D017630:Connexins / Q000037:antagonists & inhibitors / Q000502:physiology*; D003620:Dantrolene / Q000494:pharmacology; D019157:Ischemic Preconditioning, Myocardial; D007811:Lanthanum / Q000494:pharmacology; D009125:Muscle Relaxants, Central / Q000494:pharmacology; D015428:Myocardial Reperfusion Injury / Q000378:metabolism / Q000503:physiopathology*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000502:physiology*; D010455:Peptides / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
D017630:Connexins; C514423:Gap 26 peptide; D009125:Muscle Relaxants, Central; D010455:Peptides; C028521:lanthanum chloride; D007811:Lanthanum; D003620:Dantrolene; D002118:Calcium