Poloxamer 188 does not Target Altered Ca2+ Channels in Cardiomyocytes during Hypoxia/Reoxygenation Injury
Authors: Salzman Michele M. , Hackel Benjamin J. , Bartos Jason A. , Riess Matthias L. 
Published: June 2021

IntroductionIschemia/reperfusion (I/R) injury is a complex pathological event. Membrane disruptions and altered calcium (Ca2+) transport during ischemia, continue in early reperfusion. With Ca2+ being a major regulator of cardiomyocyte function, increases in intracellular Ca2+ ([Ca2+]i) can have detrimental effects. Ca2+ may not only enter through membrane disruptions, but through altered Ca2+ channels or exchangers. The tri‐block copolymer cell membrane stabilizer, Poloxamer 188 (P188), has been shown to be protective, by targeting membrane disruptions caused by I/R. However, it is not known if P188 also targets altered Ca2+ channels or exchangers. We investigated the potential role of Ca2+ channels and exchangers that may contribute to increased Ca2+ influx during ischemia, and more importantly, reperfusion. Pharmacologic compounds were used to modify Ca2+ influx, and assess the effect of P188 present during reperfusion, on these modifications.HypothesisP188, with its unique hydrophobic/hydrophilic properties, protects cardiomyocytes (CMs) against hypoxia/reoxygenation (H/R; simulated I/R) injury by stabilizing membrane disruptions and blocking altered Ca2+ channels or exchangers.MethodsIsolated CMs were kept in control/normoxic (C/N) conditions or underwent 5 hrs of hypoxia (0.01% O2; serum‐ & glucose‐free medium), then 2 hrs reoxygenation (21% O2; complete medium). The pharmacologic compounds S‐(−)‐BayK8644 (a L‐type Ca2+ channel agonist), R‐(+)‐BayK8644 (a L‐type Ca2+ channel blocker), dobutamine (a β1 receptor agonist/activator of the voltage‐gated Na+ channel), and KB‐R7943 (a blocker of the reverse mode of the Na+/Ca2+ exchanger) were used. Each was used under both C/N and H/R conditions, and added at the start of reoxygenation (or final 2 hr period in C/N conditions) ± 100μM P188. Endpoints were markers of cell number/viability and [Ca2+]i. Statistics: ANOVA and SNK post hoc comparisons, p<0.05 *vs C/N, **vs H/R, Ɨ vs vehicle.ResultsUnder C/N conditions, S‐(−)‐BayK8644 significantly increased [Ca2+]i, but dobutamine did not, over a 2 hr period. P188 had no effect on attenuating the Ca2+ influx caused by S‐(−)‐BayK8644. R‐(+)‐BayK8644 significantly decreased Ca2+ influx. Under H/R conditions, S‐(−)‐BayK8644 and dobutamine significantly increased [Ca2+]i over the 2 hr reoxygenation period. P188 had no effect on attenuating the Ca2+ influx caused by the above compounds; however, P188 did significantly decrease the Ca2+ influx caused by the H/R itself. R‐(+)‐BayK8644 and KB‐R7943 significantly decreased Ca2+ influx that occurred during the 2 hr reoxygenation period; and, when P188 was also present, this decrease in Ca2+ influx was significantly enhanced.ConclusionsIn CMs, P188 does not appear to target Ca2+ channels or exchangers when administered during reoxygenation. The protective effect of P188 most likely comes from its ability to repair membrane disruptions, and thus restore membrane integrity and cellular function.Support or Funding InformationThis work was supported by institutional funds, NIH grant (5R01 HL123227), and a Merit Review Award (I01 BX003482) from the U.S. Department of Veteran Affairs Biomedical Laboratory R&D Service.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.