. Louis MO 63110; {Departments of Artherosclerosis Therapeutics, }Biochemistry and }Chemistry Parke-Davis, Ann Arbor MI 48105 and #Department of Pharmacology, Columbia University, New York, NY 10032, U.S.A.1 15-Lipoxygenase (15-LO) has been implicated in the pathogenesis of atherosclerosis because of its localization in lesions and the many biological activities exhibited by its products. To provide further evidence for a role of 15-LO, the e ects of PD 146176 on the development of atherosclerosis in cholesterol-fed rabbits were assessed. This novel drug is a speci®c inhibitor of the enzyme in vitro and lacks signi®cant non speci®c antioxidant properties. 2 PD 146176 inhibited rabbit reticulocyte 15-LO through a mixed noncompetitive mode with a K i of 197 nM. The drug had minimal e ects on either copper or 2,2'-azobis(2-amidinopropane)hydrochloride (ABAP) induced oxidation of LDL except at concentrations 2 orders higher than the K i . 3 Control New Zealand rabbits were fed a high-fat diet containing 0.25% wt./wt. cholesterol; treated animals received inhibitor in this diet (175 mg kg 71 , b.i.d.). Plasma concentrations of inhibitor were similar to the estimated K i (197 nM). During the 12 week study, there were no signi®cant di erences in weight gain, haematocrit, plasma total cholesterol concentrations, or distribution of lipoprotein cholesterol. 4 The drug plasma concentrations achieved in vivo did not inhibit low-density lipoprotein (LDL) oxidation in vitro. Furthermore, LDL isolated from PD 146176-treated animals was as susceptible as that from controls to oxidation ex vivo by either copper or ABAP. 5 PD 146176 was very e ective in suppressing atherogenesis, especially in the aortic arch where lesion coverage diminished from 15+4 to 0% (P50.02); esteri®ed cholesterol content was reduced from 2.1+0.7 to 0 mg mg 71 (P50.02) in this region. Immunostainable lipid-laden macrophages present in aortic intima of control animals were totally absent in the drug-treated group. 6 Results of these studies are consistent with a role for 15-LO in atherogenesis.

PKC␦ leads to depressed maximum tension and cross-bridge kinetics, attributable to a dominant effect of cTnI-Thr144 phosphorylation. Our data implicate PKC␦-Tyr 311 /Thr 505 phosphorylation as dynamically regulated modifications that alter PKC␦ enzymology and allow for stimulus-specific control of cardiac mechanics during growth factor stimulation and oxidative stress. Protein kinase C␦ (PKC␦)2 is a ubiquitous serine/threonine kinase implicated in a wide range of cellular responses (1, 2). PKC␦ is conventionally viewed as a lipid-dependent enzyme that is anchored to membranes in close proximity to target substrates through interactions with lipid cofactors. However, there is recent evidence that PKC␦ also is dynamically regulated through activation loop (Thr 505 ) phosphorylation (3, 4). For other PKC isoforms, activation loop phosphorylation is a stable "priming" phosphorylation completed during de novo enzyme synthesis (5). In the case of cPKCs, activation loop phosphorylations are mediated by phosphoinositide-dependent kinase-1 and are essential to generate a catalytically competent enzyme. Although newly synthesized PKC␦ also undergoes maturational phosphoinositide-dependent kinase-1-dependent Thr 505 phosphorylation, PKC␦ differs from other PKC isoforms in that 1) PKC␦ is a catalytically active enzyme even without Thr 505 phosphorylation and 2) PKC␦-Thr 505 phosphorylation is dynamically regulated through an autocatalytic mechanism (4). Although there are hints that Thr 505 phosphorylation might contribute to the control of PKC␦ enzymology, a PKC␦-Thr 505 autophosphorylation mechanism that regulates the actions of PKC␦ toward a physiologically relevant substrate in a differentiated cell has never been reported.PKC␦ also is regulated through tyrosine phosphorylation. However, the consequences of PKC␦ tyrosine phosphorylation remain disputed, because PKC␦ tyrosine phosphorylation is variably linked to increased, decreased, or unchanged PKC␦ activity (1). Inconsistencies in the literature have been attributed to the presence of multiple tyrosine residues throughout the structure of PKC␦ (including

Background-We tested the hypothesis that I Ca,L is important to the development of cardiac memory. Methods and Results-The effects of L-type Ca 2ϩ channel blockade and ␤-blockade were tested on acutely anesthetized and on chronically instrumented, conscious dogs. Short-term memory (STM) was induced by 2 hours of ventricular pacing and long-term memory (LTM) by ventricular pacing for 21 days. STM dogs received placebo, nifedipine, or propranolol, and LTM dogs received placebo, atenolol, or amlodipine. AT 1 receptor blockade (candesartan) and ACE inhibition (trandolapril) were also tested in LTM. Microelectrodes were used to record transmembrane potentials from isolated epicardial and endocardial slabs using a protocol simulating STM in intact animals. Left ventricular epicardial myocytes from LTM or sham control dogs were dissociated, and I Ca,L was recorded (whole-cell patch-clamp technique). Evolution of STM and LTM was attenuated by I Ca,L blockers but not ␤-blockers. Neither AT 1 receptor blockade nor ACE inhibition suppressed LTM. In microelectrode experiments, pacing induced an epicardial-endocardial gradient change mimicking STM that was suppressed by nifedipine. In patch-clamp experiments, peak I Ca,L density in LTM and control were equivalent, but activation was more positive and time constants of inactivation longer in LTM (PϽ0.05). Conclusions-I Ca,L blockade but not ␤-adrenergic blockade suppresses cardiac memory. LTM evolution is unaffected by angiotensin II blockade and is associated with altered I