Thesis (Ph. D.)--University of Wisconsin--Madison, 1967. / Typescript. Vita. Description based on print version record. Includes bibliographical references.

No description available.

Quinacainol, 1-[2-(1,1-dimethylethyl)-4-quinolyl]-3-(4-piperidyl)-1-propanol is a class I antiarrhythmic agent provisionally subclassified as Ic. Studies were carried out in order to (1) determine the actions of quinacainol in acute myocardial ischæmia, (2) ascertain the mechanism(s) responsible for these actions, and (3) ascertain the appropriateness of its subclassification. Toxicological, hæmodynamic, and ECG effects in chronically prepared conscious rats were determined following administration of 1, 2, 4, or 8 mg/kg of quinacainol given i.v. over 10 minutes on alternate days. Toxicity referable to the heart was seen at doses of 8 mg/kg and above. In rats given 8 or 16 mgkg, arrhythmias occurred. Quinacainol had no major effects on blood pressure, unlike most class I antiarrhythmics, but lowered heart rate (not statistically significantly) and prolonged P-R interval and QRS duration. In an attempt to protect against ischæmic arrhythmias, doses of 2 mg/kg and 4 mg/kg were given. The high dose gave the best protection. It reduced the incidence of ventricular tachycardia (VT) from a control value of 80% to 30%, and reduced the incidence of ventricular fibrillation (VF) from a control value of 60% to 10%. An increase in the incidence of premature ventricular contractions was seen at both doses. Blood pressure was not adversely effected although slight bradycardic effects as well as prolongation of the P-R interval were seen at both doses. Both doses reduced S-T segment and delayed onset of elevation of S-T segment and R-wave which were induced by coronary occlusion. Sensitivity to electrical stimulation was tested in pentobarbital anæsthetised rats using ventricular electrodes. Doses of 0.5, 1, 2, and 4 mg/kg were given cumulatively as a 10 min infusion every 25 min. Quinacainol did not affect QRS duration or the Q-Tc interval but dose-dependently widened P-R interval when compared to pretreatment. Quinacainol dose-dependently increased threshold current, threshold duration, and ventricular fibrillation threshold. In addition, quinacainol elevated effective refractory period while decreasing maximum following frequency. Open-chest rats under pentobarbital anæsthesia were used to record the effects of quinacainol on epicardial intracellular potentials. Recordings were made by conventional microelectrode techniques before and after cumulative doses of 0.5, 1, 2, 4, and 8 mg/kg i.v. Quinacainol dose-dependently reduced phase zero of the action potential (AP) and AP height but did not influence other phases of the AP (with the exception of prolonging repolarization at the highest dose); actions indicative of class Ic. Effects of quinacainol on isolated rat hearts were assessed using a modified Langendorff heart preparation and were compared with those of tetrodotoxin (TTX). Quinacainol widened the P-R interval and QRS duration without having major effect on the Q-Tc interval. In addition it slowed the sinus beating rate. Quinacainol was more potent than TTX. All findings indicated that quinacainol is a potent antiarrhythmic agent with Na⁺channel blocking properties. / Medicine, Faculty of / Anesthesiology, Pharmacology and Therapeutics, Department of / Graduate

The structural and functional consequences of the interaction of various antiarrhythmics with human erythrocyte membranes, guinea pig brain synap-tosomes and myocardial sarcolemmal membranes were studied at drug concentrations affecting the stability of intact erythrocytes to hypotonic lysis. It was assumed that such stabilization might bear some molecular resemblance to the electrical stabilizing properties of these drugs in excitable tissues. Membrane perturbational actions of these drugs were measured in terms of the specific incorporation of the chromophoric probes, 5,51-dithio-bis-(2-nitrobenzoic acid) (DTNB) and trinitrobenzenesulfonic acid (TNBS) into membrane sulfhydryl and amino groups respectively. Most drugs tested, including lidocaine, quinidine, the verapamil analogue D-600 and the quaternary analogues QX 572 and pranolium, exhibited a concentration-dependent stimulation of DTNB and TNBS incorporation. At drug concentrations producing erythrocyte stabilization, the protein perturbational properties of quinidine, lidocaine, D-600 and QX 572 as viewed in terms of DTNB labelling were equivalent while differences were apparent with quinidine, D-600 and lidocaine at high concentrations in the destabilizing range. Most agents, with the exception of pranolium, showed a similar pattern of DTNB incorporation in brain synaptic membranes as in erythrocytes. Studies of the incorporation of TNBS into erythrocyte membranes indicated that antiarrhythmics induce greater structural alterations in membrane phospholipids as compared with membrane proteins. Bretylium and practolol, two substances with minimal direct cardiodepressant properties, did not enhance DTNB or TNBS incorporations into erythrocyte membranes, although both agents, especially practolol, possessed marked antihemolytic properties. It appeared, therefore, that the membrane perturbational actions of antiarrhythmics as analyzed here by means of group-specific chemical probes are a better index of their direct myocardial membrane actions than erythrocyte stabilization. The functional consequences of drug-membrane interaction as reflected in the inhibition of membrane-associated enzymes by antiarrhythmics were shown to be critically dependent on the drug and membrane in question. The activity of erythrocyte membrane ouabain-sensitive K+-stimulated p-nitrophenyl-phosphatase (K+-NPPase) was more readily inhibited than that of Mg++-independent and Mg++-stimulated NPPase by most drugs examined. In myocardial sarcolemmal membranes, lidocaine was stimulatory to the K+-NPPase whereas all other agents exhibited stimulatory actions only at the lowest drug concentrations. The Ca++-ATPase system in the erythrocyte membrane was also inhibited by antiarrhythmics with propranolol, pranolium and lidocaine showing a relatively higher degree of inhibition of the high Ca++ affinity component while quinidine and D-600 exerted equal inhibitory actions on both high and low Ca++ affinity components of the enzyme. A comparison of the perturbational actions of antiarrhythmics in isolated erythrocyte membranes, in the membranes of the intact erythrocyte and in brain synaptic membranes was made by analyzing the effects of drugs on the activity of the membrane acetylcholinesterase present in these preparations. Inhibitory actions of all drugs tested were comparable in both intact and isolated erythrocyte membranes but differed in the excitable tissue membrane. The nature of the inhibition exerted by the antiarrhythmics on acetylcholinesterase of intact erythrocytes was of a mixed type for most drugs except practolol which inhibited non-competitively. The transmembrane chloride gradient had no influence on the inhibition by bretylium, lidocaine and D-600 of the acetylcholinesterase activity of the intact cells but the inhibition produced by quinidine and propranolol was enhanced when erythrocytes were suspended in a low chloride medium. The foregoing results, therefore, indicate that the membrane perturbational actions of antiarrhythmics vary with the agent in question and with the particular membrane system. It is suggested that the molecular mechanisms by which these drugs alter cardiac automaticity may not be identical and may differ in various regions of the myocardium. This in turn may underlie the differing spectra of clinical effectiveness exhibited by these pharmacological agents. / Medicine, Faculty of / Anesthesiology, Pharmacology and Therapeutics, Department of / Graduate

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published_or_final_version / Community Medicine / Master / Master of Public Health

No description available.

The cardiac ryanodine receptor (RyR2) plays a key role in excitation-contraction coupling (ECC). Mutations in RyR2 are known to be linked to the arrhythmogenic disorder, catecholaminergic polymorphic ventricular tachycardia (CPVT), a deadly disease which is characterized by a leak of calcium from sarcoplasmic reticulum and a decrease in calmodulin (CaM) binding. A novel drug, 84F2, shown to inhibit arrhythmias in RyR2-R176Q heterozygous CPVT mouse hearts (2.5 µg/kg), decrease spark frequency in cells derived from CPVT mice (IC50 = 35 nM), and inhibit RyR2 single channel activity at low nanomolar concentrations (IC50 = 8 nM). When CaM is added back to RyR2, 84F2's ability to inhibit channel activity is suppressed approximately 250 fold. A metabolite of 84F2, 78F3, is shown to also be active in the inhibition of RyR2. We propose that 84F2 decreases arrhythmias by binding to the CaM deficient RyR2, but does not affect normal ECC when CaM is present. This work characterizes for the first time a class of drugs whose inhibitory affects are dependent upon the removal of CaM from RyR2.

Reversible protein phosphorylation is an essential component of metazoan signaling and cardiovascular physiology. Protein kinase activity is required for regulation of cardiac ion channel and membrane receptor function, metabolism, and transcription, and aberrant kinase function is widely observed across disparate cardiac pathologies. In fact, multiple generations of cardiac therapies (eg. beta-adrenergic receptor blockers) have targeted cardiac kinase regulatory cascades. In contrast, essentially nothing is known regarding the mechanisms that regulate cardiac phosphatase activity at baseline or in cardiovascular disease. Protein phosphatase 2A (PP2A) is a key phosphatase with multiple roles in cardiac physiology. Here we demonstrate the surprisingly complex regulatory platforms that control PP2A holoenzyme activity in heart. We present the first full characterization of the expression and regulation of the PP2A family of polypeptides in heart. We identify the expression of seventeen different PP2A genes in human heart and define their differential expression and distribution across species and in different cardiac chambers. We show unique subcellular distributions of PP2A regulatory subunits in myocytes, strongly implicating the regulatory subunit in conferring PP2A target specificity in vivo. We report striking differential regulation of PP2A scaffolding, regulatory, and catalytic subunit expression in multiple models of cardiovascular disease as well as in human heart failure samples. Importantly, we demonstrate that PP2A regulation in disease extends far beyond expression and subcellular location, by identifying and describing differential post-translational modifications of the PP2A holoenzyme in human heart failure. Furthermore, we go to characterize a mechanism for this method of post-translational modification that may represent a pathway capable of being therapeutically manipulated in human heart failure. Lastly we provide evidence that dysregulation of phosphatase activity contributes to the cellular pathology associated with a previously described inheritable human arrhythmia syndrome, highlighting the importance of the PP2A in cardiovascular physiology and disease. Together, our findings provide new insight into the functional complexity of PP2A expression, activity, and regulation in heart and in human cardiovascular disease and identify potentially new and specific gene and subcellular targets for the treatment of human arrhythmia and heart failure.

Reversible protein phosphorylation is an essential component of metazoan signaling and cardiovascular physiology. Protein kinase activity is required for regulation of cardiac ion channel and membrane receptor function, metabolism, and transcription, and aberrant kinase function is widely observed across disparate cardiac pathologies. In fact, multiple generations of cardiac therapies (eg. beta-adrenergic receptor blockers) have targeted cardiac kinase regulatory cascades. In contrast, essentially nothing is known regarding the mechanisms that regulate cardiac phosphatase activity at baseline or in cardiovascular disease. Protein phosphatase 2A (PP2A) is a key phosphatase with multiple roles in cardiac physiology. Here we demonstrate the surprisingly complex regulatory platforms that control PP2A holoenzyme activity in heart. We present the first full characterization of the expression and regulation of the PP2A family of polypeptides in heart. We identify the expression of seventeen different PP2A genes in human heart and define their differential expression and distribution across species and in different cardiac chambers. We show unique subcellular distributions of PP2A regulatory subunits in myocytes, strongly implicating the regulatory subunit in conferring PP2A target specificity in vivo. We report striking differential regulation of PP2A scaffolding, regulatory, and catalytic subunit expression in multiple models of cardiovascular disease as well as in human heart failure samples. Importantly, we demonstrate that PP2A regulation in disease extends far beyond expression and subcellular location, by identifying and describing differential post-translational modifications of the PP2A holoenzyme in human heart failure. Furthermore, we go to characterize a mechanism for this method of post-translational modification that may represent a pathway capable of being therapeutically manipulated in human heart failure. Lastly we provide evidence that dysregulation of phosphatase activity contributes to the cellular pathology associated with a previously described inheritable human arrhythmia syndrome, highlighting the importance of the PP2A in cardiovascular physiology and disease. Together, our findings provide new insight into the functional complexity of PP2A expression, activity, and regulation in heart and in human cardiovascular disease and identify potentially new and specific gene and subcellular targets for the treatment of human arrhythmia and heart failure.