title: Inhibition of L-type Ca2+ channel current and negative inotropy induced by arachidonic acid in adult rat ventricular myocytes.
abstract: We have previously shown an increase in arachidonic acid (AA) release in response to proinflammatory cytokines in adult rat ventricular myocytes (ARVM). AA is known to alter channel activities; however, its effects on cardiac L-type Ca(2+) channel current (I(Ca,L)) and excitation-contraction coupling remain unclear. The present study examined effects of AA on I(Ca,L), using the whole cell patch-clamp technique, and on cell shortening (CS) and the Ca(2+) transient of ARVM. I(Ca,L) was monitored in myocytes held at -70 mV and internally equilibrated and externally perfused with Na(+)- and K(+)-free solutions. Exposure to AA caused a voltage-dependent block of I(Ca,L) concentration dependently (IC(50) 8.5 microM). The AA-induced inhibition of I(Ca,L) is consistent with its hyperpolarizing shift in the voltage-dependent properties and reduction in maximum slope conductance. In the presence of AA, BSA completely blocked the AA-induced suppression of I(Ca,L) and CS. Intracellular load with AA had no effect on the current density but caused a small depolarizing shift in the I(Ca,L) activation curve, suggesting a site-specific action of AA. Moreover, intracellular AA had no effect on the extracellular AA-induced decrease in I(Ca,L). Pretreatment with indomethacin, an inhibitor of cyclooxygenase, or addition of nordihydroguaiaretic acid, an inhibitor of lipoxygenase, had no effect on AA-induced changes in I(Ca,L). Furthermore, AA suppressed CS and Ca(2+) transients of intact ARVM with no significant effect on SR function and myofilament Ca(2+) sensitivity. Therefore, these results suggest that AA inhibits contractile function of ARVM, primarily due to its direct inhibition of I(Ca,L) at an extracellular site.
authors.affiliation: Dept. of Pharmaceutical Sciences and Dept. of Pharmacology & Toxicology, Univ. of Arkansas for Medical Sciences, 4301 West Markham St. MS 522-3, Little Rock, AR 72205, USA. sliu@uams.edu
authors.forename: Shi J
authors.initials: SJ
authors.lastname: Liu
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000378:metabolism* / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D002478:Cells, Cultured; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006352:Heart Ventricles / Q000166:cytology / Q000378:metabolism; D007213:Indomethacin / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects; D016859:Lipoxygenase Inhibitors / Q000494:pharmacology; D008297:Male; D009637:Masoprocol / Q000494:pharmacology; D008564:Membrane Potentials; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D012710:Serum Albumin, Bovine / Q000378:metabolism