Inhibition of sarcoplasmic reticular function by chronic interleukin-6 exposure via iNOS in adult ventricular myocytes.
Interleukin (IL)-6 has been shown to decrease cardiac contractility via a nitric oxide synthase (NOS)-dependent pathway during acute exposure. We previously reported that IL-6 decreases contractility and increases inducible NOS (iNOS) in adult rat ventricular myocytes (ARVM) after 2 h exposure. The goal of this study was to investigate the cellular mechanism underlying this chronic IL-6-induced negative inotropy and the role of iNOS. Pretreatment for 2 h with 10 ng ml-1 IL-6 decreased the kinetics of cell shortening (CS) and contractile responsiveness to Ca2+o ([Ca2+]o from(0) to 2 mM) in ARVM. We first examined whether IL-6 reduced Ca2+ influx via L-type Ca2+ -channel current (ICa,L). Whole-cell ICa,L in ARVM was measured under conditions similar to those used for CS measurements, and it was found to be unaltered by IL-6. The sarcoplasmic reticular (SR) function was then assessed by examining postrest potentiation (PRP) and caffeine responsiveness of CS. Results showed that treatment with IL-6 for 2 h significantly decreased PRP, which was concomitant with a decrease in the phosphorylation of phospholamban. Following removal of IL-6, PRP and responsiveness to 10 mM caffeine were also reduced. Meanwhile, the IL-6-induced increase in nitric oxide (NO) production after 2 h (but not 1 h) was abolished by NG-monomethyl-l-arginine (l-NMMA) and 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT; a selective inhibitor of iNOS). Furthermore, IL-6-elicited suppressions of PRP and responsiveness to caffeine and Ca2+o were abolished by L-NMMA and AMT. Thus, these results suggest that activation of iNOS mediates IL-6-induced inhibition of SR function in ARVM during chronic exposure.
Yu
Xin-Wen
XW
Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, 4301 West Markham Street , Little Rock, AR 72205, USA.
Chen
Qian
Q
Kennedy
Richard H
RH
Liu
Shi J
SJ
D000818:Animals; D019138:Antibodies, Blocking / Q000494:pharmacology; D015153:Blotting, Western; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000378:metabolism; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D066298:In Vitro Techniques; D015850:Interleukin-6 / Q000494:pharmacology*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D009569:Nitric Oxide / Q000096:biosynthesis; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012519:Sarcoplasmic Reticulum / Q000187:drug effects* / Q000201:enzymology; D000099211:Phospholamban; D000093242:Interleukin-6 Inhibitors
D019138:Antibodies, Blocking; D002110:Caffeine; D002118:Calcium; D002135:Calcium-Binding Proteins; D000697:Central Nervous System Stimulants; D015850:Interleukin-6; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D000099211:Phospholamban; D000093242:Interleukin-6 Inhibitors; C496318:Nos2 protein, rat