Palmitoylcarnitine increases [Na+]i and initiates transient inward current in adult ventricular myocytes.
This study was performed to determine whether long-chain acylcarnitines, specifically palmitoylcarnitine, could account for the increase in intracellular Na+ ([Na+]i) during ischemia eliciting a secondary increase in intracellular Ca2+ ([Ca2+]i). Accordingly, whole cell voltage-clamp procedures and Na(+)-sensitive electrode recordings were employed simultaneously in isolated adult rabbit ventricular myocytes to assess the relationship between activation of a slow-inactivating Na+ current [INa(s)] and a potential increase in [Na+]i. The [Na+]i increased progressively from 8.4 +/- 1.2 to 22.5 +/- 1.8 mM (n = 8, P < 0.01) on exposure to palmitoylcarnitine (10 microM) accompanied by the activation of INa(s); both effects were reversible. Inhibition of INa(s) by tetrodotoxin (TTX, 10 microM) inhibited the increase in [Na+]i. Increasing [Na+]i to 20 mM without ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) to mimic effects measured with palmitoylcarnitine consistently elicited the transient inward current (Iti) and delayed afterdepolarizations (DADs). The percent inhibition (12.9 +/- 2.8%) of the Na(+)-K(+)-adenosinetriphosphatase pump activity by palmitoylcarnitine (10 microM) was much smaller than that induced by ouabain (10 microM, 90.5 +/- 2.5%), suggesting that this modest effect of palmitoylcarnitine on the pump is unlikely to account for the increase in [Na+]i induced by palmitoylcarnitine. Thus palmitoylcarnitine induces the INa(s) leading to an increase in [Na+]i, which elicits an increase in [Ca2+]i probably via the Na+/Ca2+ exchanger, thereby leading to the development of Iti and DADs.
Wu
J
J
Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Corr
P B
PB
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D004594:Electrophysiology / Q000379:methods; D005260:Female; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006352:Heart Ventricles; D066298:In Vitro Techniques; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009532:Nickel / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D010172:Palmitoylcarnitine / Q000494:pharmacology*; D011817:Rabbits; D012508:Sarcolemma / Q000201:enzymology; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors
D010172:Palmitoylcarnitine; D013779:Tetrodotoxin; D004533:Egtazic Acid; D010042:Ouabain; C022838:nickel chloride; D009532:Nickel; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium