When cellular stimulants such as neurotransmitters, hormones, autacoids, cytokines and growth factors stimulate their respective specific receptors in the plasma membranes of cells, a variety of responses are elicited. GTP-binding proteins are also involved in the reactions between receptors and cellular effectors. Stimulation of receptors are subsequently coupled to the activation of ion channels, turnover of inositol phospholipid metabolism, adenylate cyclase and guanylate cyclase, inhibition of adenylate cyclase and potentiation of all proliferation. Active substances such as the so-called second messengers are produced in the cells. In this article, two findings are described: 1) Ca2+, which increases by stimulation of receptors with neurotransmitters and hormones, stimulated Ca2+/calmodulin-dependent protein kinase II in cell systems such as NG108-15 neuroblastoma × glioma hybrid cells and primarily cultured neuronal cells of rat hippocampus. 2) Coupling preferences and possible transduction mechanisms from experiments on NG108-15 cells and NL308 neuroblastoma × fibroblast hybrid cells which have been stably transfected with DNA for ml, m2, m3 and m4 muscarinic acetylcholine receptors were examined. These results may provide a useful research model for examining and evaluating the effects and mechanisms of the drugs on a living system and may help develop useful methodology for the discovery of innovative drugs.
This review is derived from the symposium held at the 66th Annual Meeting of the Japanese Pharmacological Society (March, 1993). The symposium consisted of six invited papers whose general theme was the application of recently found ATPase inhibitors selective to SR and ER-Ca2+-ATPase to the analyses of the physiological and pharmacological roles of endoplasmic and sarcoplasmic reticulum Ca stores. Inhibitors used were: thapsigargin, cyclopiazonic acid, 2, 5-di-(t-butyl)-1, 4-benzohydroquinone and 3', 3", 5', 5"-tetraiodosulfophthalein. Gingerol was found to facilitate the action of the ATPase. In either smooth, cardiac or skeletal muscle, sympathetic neurons or several cell lines these inhibitors affected a variety of cell functions and conditions such as contraction, ionic conductance and excitability of the plasma membrane, regulation of intracellular free Ca2+ concentration, transport of viral glycoprotein to the cell surface. Many of these studies utilized either single or cultured cell preparations or skinned muscle. These inhibitors were shown to be useful tools for investigating the SR and ER functioning as Ca sources or Ca sequestrating pumps, and further for estimating the contribution of ER or SR to regulating the flux of Ca2+ and other ions through the plasma membrane. Results of analyses using these inhibitors are discussed.
In this paper, we briefly review current topics about smooth muscle with regards to Ca2+ release, Ca2+ sensitization, and Ca2+ regulation of contraction. Inositol 1, 4, 5-trisphosphate releases Ca2+ from the sarcoplasmic reticulum, where Ca2+-dependent immediate feedback control may work. However, the involvement of this feedback control in the Ca2+-induced Ca2+ release mechanism remains to be elucidated. Either agonist or GTP γ S is known to increase the Ca2+ sensitivity of myofilaments. The agonist-induced Ca2+ sensitization could be explained by the up-regulation due to myosin light chain kinase or by the down-regulation due to myosin light chain phosphatase. The GTP γ S-induced Ca2+ sensitization seems to be mediated by rho A p21, a small G protein. Thus, myosin phosphorylation is not the obligatory way to regulate the actin-myosin interaction. We propose that cross-linking between actin and myosin may work as an alternative way to regulate the interaction from biochemical studies. The candidates for the cross-linkers are caldesmon, calponin and myosin light chain kinase. The inhibitory effect of Ca2+ on the interaction, which is observed under the specific conditions for measuring smooth muscle contraction, may hold the key to finding the physiological significance of the cross-linking activity.
Development of novel drugs relies on research to discover new drugs. Testing and evaluating new drugs on human subjects are usually impossible because of ethical concerns. Therefore, for drug discovery research, it is essential to establish animal models of human diseases. Numerous animal models have been developed and used in drug discovery and evaluation studies. Such animal models have had important roles in developing new drugs as well as understanding the etiologies of diseases. In the field of cardiovascular drugs, several interesting animal models are currently in use. These include, transgenic mice carrying both human renin and human angiotensinogen genes, Watanabe's heritable hyperlipidemic rabbits, rats with pulmonary hypertension induced by monocrotaline, myocardial infarction model, cardial hypertrophy model and photochemical thrombosis models. It is envisaged that for drug discovery and development, the search for more physiological animal models will continue in the future.
The pressure and flow produced by circulating blood as well as contractions of the heart and blood vessels act as biomechanical stimuli on the cardiovascular system. The cardiovascular response to the hemodynamic stimuli is a type of physical reception and a subsequent reaction, and thus touches the core of up-to-date problems, including cellular signaling and the interaction between the blood and endothelium and/or medial smooth muscles. Pathophysiological conditions such as vasospasm, hypertension, cardiac arrhythmia and myocardial hypertrophy, and atherosclerosis, are also caused by abnormal biomechanical stimuli. The present article summarizes the papers presented at the congress symposium of the 66th Annual Meeting of the Japanese Pharmacological Society, in which the present status and the future prospects of current research fields such as shear stress and endothelial function, regulation of blood pressure and flow, myogenic tone, mechanosensitive ion channels, and clinical implications of high and low shear stress and hemodynamic overload were actively discussed. These studies will surely open the way to an era for the development of new drugs, and improvements in the knowledge about the hemodynamic mechanisms in health and disease.
The Cardiac Arrhythmia Suppression Trial (CAST) casted serious doubts on the usefulness of Class I antiarrhythmic drugs, causing us to turn our attention from drugs impairing conduction of excitation in the myocardium by blocking sodium channels toward those producing increased refractoriness of myocardial cells by blocking potassium channels. This change in the direction of thinking from the “Na+ channel paradigm” to “K+ channel paradigm” resulted in the generation of newly synthetized Class III drugs that have the common electrophysiological property of suppressing outward K+ currents (IK, IK1, Ito) without affecting inward currents (INa, Ica). However, their reversed use-dependence of action potential duration prolonging effect contributes to their untoward action of proarrhythmias. It is still controversial if ion channel blockers acting solely on a certain kind of ion channels are more beneficial than drugs having compound actions such as amiodarone or sotalol. Molecular biology, if combined with arrhythmology, is expected to provide new chemical and pharmacological bases for creating novel antiarrhythmic drugs.
The physiological characteristics and significance of long-term potentiation in the hippocampus were summarized. In particular, it was pointed out that different mechanisms are involved in the production of hippocampal LTP between the mossy fiber-CA3 system and other systems such as Schaffer collateral-CA1, fimbrial fiber-CA3 and commissural/associational fiber-CA3. Furthermore, the ε-subspecies of protein kinase C (PKC) was demonstrated to be exclusively located at the presynaptic terminals in the hippocampus and activated by arachidonic acid, and this enzyme is suggested to be involved in the production of LTP through a phosphorylation of GAP-43, while the γ-subspecies of PKC may be postsynaptically involved in LTP through an activation of NMDAR1. The production of LTP in the hippocampus is facilitated by many factors such as epidermal growth factor, fibroblast growth factors, somatostatin, M1 receptor agonists and many drugs like anirasetam, bifemelane, idebenone, indeloxazine and vinpocetine, but inhibited by M2-receptor agonists, scopolamine and midazolam. In addition to electrophysiological methods, LTP-like phenomena in 2-deoxyglucose uptake and leucine incorporation can be detected. These LTP phenomena in several animal models will be useful as indices for evaluating facilitatory actions of various compounds on learning/memory functions.
This review article describes the effect and mechanism of various antisecretory drugs. Both histamine H2-receptor antagonists and gastric proton pump inhibitors are now world-widely used as the first choice for the treatment of acid-related diseases. Because of their potential effectiveness in inhibiting gastric acid secretion, new H2-antagonists and pump inhibitors are under development with the aim of mitigating of the side effects. The local antisecretory effects of FPL-52694, NC-1300-O-3 and ME 3407, which were demonstrated in Heidenhain pouch dogs, will provide clues for the development of new types of antisecretory drugs. Antigastrin drugs are also promising.
The efficacy and toxicity of drugs are closely related to the kinetics and metabolism of drugs. The metabolism of drugs is variable depending on individual, age, sex and species differences. Therefore, in this paper, the following strategies of drug metabolism studies on each phase of development of new drugs is discussed: 1. Early selection of drug candidates for the development of new drugs by a preliminary drug metabolism study. 2. Selection of a drug candidate for the repeated administration of drug toxicity study. 3. Drug metabolism studies on sex- and species-related differences in experimental animals. 4. Drug toxicity and metabolic activation of drug candidates. 5. In vitro and in vivo drug metabolism studies in humans. 6. Arrangement of drug metabolism and pharmacokinetic profile of drug candidate for the phase I study. 7. Role of pharmacokinetics and drug metabolism studies in the phase I study. 8. Pharmacokinetic and metabolic studies for the development of chiral drugs. 9. Approach to drug design from the viewpoint of drug metabolism studies. In conclusion, performance of drug metabolism studies starting from the early stage of drug development is a powerful and useful tool to increase the efficiency and to minimize the period and cost for the development of new drugs.