Katsuharu Tsuchida

The anti-emetic activity of GK-128 in Suncus murinus.

In Suncus murinus, various emetic responses and the anti-emetic activity of a new 5-hydroxytryptamine3 (5-HT3) receptor antagonist, GK-128 (2-[(2-methylimidazol-1-yl) methyl benzo[f]thiochromen-1-one monohydrochloride hemihydrate), were investigated. Cancer chemotherapeutic agents, cisplatin and cyclophosphamide, dose-dependently induced emesis of long-lasting duration. The 5-HT3 receptor agonist, 2-methyl-5-HT, and copper sulfate also induced emesis of short duration. However, another 5-HT3 receptor agonist, m-chlorophenylbiguanide, was not consistently emetic. GK-128 inhibited the emetic responses induced by chemotherapeutic agents and 2-methyl-5-HT with similar potency. The anti-emetic action of GK-128 was more potent than that of ondansetron, Y-25130, granisetron and metoclopramide. The order of potency of these drugs, except granisetron, was consistent with that of their 5-HT3 receptor binding affinity in rat cortex. GK-128 failed to inhibit copper sulfate-induced emesis. These data suggest that GK-128 has a potent inhibitory effect on emesis via the 5-HT3 receptor, and that the 5-HT3 receptor involved in emesis in Suncus murinus may be different from the classically defined 5-HT3 receptor in other animals such as rats, dogs and ferrets.

Electrophysiological actions of A23187 and X-537A in spontaneously beating and in voltage-clamped rabbit sino-atrial node preparations

SummaryElectrophysiological effects of calcium ionophores, A23187 and X-537A, on spontaneously beating and voltage-clamped rabbit sino-atrial node preparations were examined, using the voltage-clamp technique with two microelectrodes. (1)A23187 (administered cumulatively) increased the cycle length significantly at 3 × 10−6 and 10−5 mol/l, and X-537 only at 10−5 mol/l. Other action potential parameters were unaffected in the presence of these concentrations of either agent. At 2 × 10−5 mol/l, either agent prolonged the cycle length significantly, but increased the amplitude and the duration of the action potentials and the maximum diastolic potential not to any significant extent. Both X-537A and A23187, at 2 × 10−5 mol/l, induced a dysrhythmia, which in the former was probably due to delayed afterdepolarizations.(2)In voltage-clamped sino-atrial node cells, the holding current was shifted outwardly, to a greater extent in the presence of X-537A than A23187 at the same concentration (2 × 10−5 mol/l). The ionophores initially increased the slow inward current and then decreased it. The steady outward current was inhibited, and its activation curve was shifted to a more negative voltage range. X-537A caused a transient inward current and an inward tail current on repolarization to the holding potential.(3)At concentrations of 10 and 18 mmol/l [Ca2+]o or in the presence of isoprenaline 10−7 mol/l, these ionophores induced a more severe dysrhythmia. Conversely in the nominal absence of [Ca2+]o the regular rhythm was resumed.(4)These findings suggest that the calcium ionophores may induce a calcium overload intracellularly due to increases in not only Ca2+ transport into cell but also the slow inward current and Ca2+ release from internal stores, and may then modify the conductance of potassium channels due to elevation of [Ca2+]i.

Inhibitory effect of TS-962 on the formation of early atherosclerotic lesions in high fat-fed hyperlipidemic hamsters.

The hypocholesterolemic and anti-atherosclerotic effect of TS-962, a specific ACAT inhibitor, was investigated in a hamster model fed a high fat diet containing 10% coconut oil and 0.05% cholesterol. Lipid accumulated atherosclerotic lesions were detected by using oil red O staining in the lesion-prone aortic arch. A high dose, estimated to be 15 mg/kg, of TS-962 decreased serum cholesterol to normal levels with reduction of liver cholesterol contents below normal levels, and as a consequence, entirely inhibited the lipid accumulation in the aortic arch. Furthermore, a low dose, estimated to be 1.5 mg/kg, of TS-962 remarkably inhibited aortic lipid accumulation by 73% compared with the control group, without changing either serum cholesterol level or liver cholesterol content. These findings suggest that TS-962 is effective in the primary prevention of atherosclerosis by directly suppressing the formation of foam cells in arteries.

Potassium currents in ventricular myocytes from genetically diabetic rats

Our previous study demonstrated the longer duration of action potential in ventricular myocytes from genetically diabetic WBN/Kob rats without change in calcium channel density compared with age-matched controls [Tsuchida, K., H. Watajima, and S. Otamo. Am. J. Physiol. 267 (Heart Circ. Physiol. 36): H2280-H2289, 1994]. In the present study we examined the alteration of potassium currents, especially transient outward current, in ventricular myocytes of genetically diabetic WBN/Kob rats. WBN/Kob rats gradually develop hyperglycemia with aging and show some similarity to non-insulin-dependent diabetes mellitus models, which differ from the insulin-dependent streptozotocin-treated rat model. The density of the intracellular calcium ion-independent transient outward current (I(to)) from 17- to 19-mo diabetic rat myocytes was significantly smaller than that from age-matched control rat myocytes. In addition, the density of I(to) from 17- to 19-mo rat myocytes was significantly less than that from 2-mo rat myocytes, suggesting that aging-induced alteration of I(to) was accelerated by the diabetic state. The steady-state inactivation curves of I(to), the recovery from I(to) inactivation, and the other outward currents were not significantly altered between diabetic myocytes and age-matched control myocytes. In conclusion, the prolonged duration of action potential from genetically diabetic rat myocytes is mainly due to the depressed I(to).

Changes in responsiveness of the aorta to vasorelaxant agents in genetically diabetic rats: a study in WBN/Kob rats.

The effects of various vasorelaxant agents on aortas from control and genetically diabetic rats were examined. The concentration-response curves for the isoproterenol (ISO)-induced relaxation of both aortic strips with and without endothelium are shifted to the right in diabetic rats. The relaxation responses of diabetic aorta to forskolin and vasoactive intestinal peptide did not differ from those of controls. The relaxation responses of diabetic aorta to cromakalim and nicorandil did not differ from those of controls. These results indirectly indicate that ISO-induced relaxation responses of the aortic strips from genetically diabetic rats decreased, and that this decreased relaxation response of the strips to ISO may be due to decreased density or affinity of beta adrenoceptors on the endothelium and vascular smooth muscle.

HL-004, the ACAT inhibitor, prevents the progression of atherosclerosis in cholesterol-fed rabbits

HL-004, N-(2,6-diisopropylphenyl) tetradecylthioacetamide, a novel acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, was evaluated concerning the possible prevention of hyperlipidemia and atherosclerosis in 1% cholesterol-fed rabbits. HL-004 (0.2, 5 and 25 mg/kg) was orally administered once a day for 12 weeks. HL-004 inhibited the rise of total serum cholesterol at a dose of 5 mg/kg and over. In the thoracic aorta, HL-004 at the doses of 5 mg/kg and 25 mg/kg reduced the total cholesterol content by 56.3% and 84.2% compared with control, and decreased ACAT activity, dose-dependently. HL-004 also attenuated the development of aortic lesions. The area of atherosclerotic lesions was reduced by 30.3% with 5 mg/kg of HL-004 and 100% with 25 mg/kg. In this study, we suggest that the main reason for HL-004 preventing the progression of atherosclerosis is its hypocholesterolemic effect due to the inhibition of cholesterol absorption in the intestine.

Comparison of a calcium antagonist, CD-349, with nifedipine, diltiazem, and verapamil in rabbit spontaneously beating sinoatrial node cells

Effects of CD-349, a novel 1,4-dihydro-pyridine, and other calcium antagonists on membrane potentials in spontaneously beating and the membrane currents in voltage-clamped rabbit sinoatrial (SA) node cells were examined. CD-349 10-8 M significantly decreased the maximum rate of depolarization and prolonged action potential duration (APD) and the cycle length (CL) without affecting action potential (AP) amplitude (APA) and maximum diastolic potential (MDP). CD-349 affected only the last part of pacemaker potential (phase 4 depolarization) and then lengthened the cycle. These effects of CD-349 became accentuated as the drug concentration increased. Sinus arrest occurred in two of five preparations at 10 -7 M, and occurred in all preparations at a concentration of 10 -6 M. The concentration inducing arrest of CD-349 was about one-tenth lower as compared with that of nifedipine. In voltage-clamped SA node cells, CD-349 in concentrations of 3 × 10-8 and 10 -7 M decreased the slow inward current; the steady-state outward current and the hyperpolarization-activated inward current were also reduced, but less markedly. Nifedipine decreased the slow inward current, the potency of which was one third less than that of CD-349. Diltiazem and verapamil were weaker in prolonging cycle length and in inducing arrest as compared with CD-349 and nifedipine. These results suggest that CD-349 is a more potent calcium antagonist for decreasing pacemaker activity of rabbit SA node cells as compared with the other three calcium antagonists tested.

Impairment of Endothelium-dependent Relaxation and Changes in Levels of cyclic GMP in Carotid Arteries from Stroke-prone Spontaneously Hypertensive Rats

Abstract— Endothelium‐dependent relaxation of carotid arteries and changes in levels of cyclic (c)GMP between stroke‐prone spontaneously hypertensive (SHRSP) and Wistar‐Kyoto (WKY) rats have been compared. The concentration‐response curve for acetylcholine (ACh)‐induced relaxation was shifted to the right in carotid arteries from SHRSP. Relaxation responses produced by calcimycin (A 23187) and melittin, both endothelium‐dependent agents, were depressed in carotid arteries from SHRSP. Relaxation responses produced by sodium nitroprusside and 8‐Br‐cGMP were similar to those in strips from WKY. ACh‐induced production of cGMP was significantly decreased in carotid arteries from SHRSP when compared with the level for similarly treated strips from WKY. These results suggest that functional changes in endothelium, but not guanylate cyclase activity or cGMP sensitivity in the carotid arteries, may occur in hypertension. Thus, impaired endothelium‐dependent relaxation in SHRSP may play an important role in hypertensive vascular diseases such as stroke.

Effects of VA-045, a novel apovincaminic acid derivative, on isolated blood vessels: Cerebroarterial selectivity

We investigated the effects of VA-045, an apovincaminic acid derivative, on isolated blood vessels. VA-045 (10(-7)-10(-5) M) and vinpocetine (10(-7)-10(-5) M) inhibited the 64 mM KCl-induced and 10(-6)M norepinephrine (NE)-induced contraction of rat aortic strips. VA-045 (10(-7)-10(-4) M) and vinpocetine (10(-7)-10(-4) M) inhibited the activity of cyclic AMP and cyclic GMP phosphodiesterase in porcine coronary artery. VA-045 (3 x 10(-9-3 x 10(-6) M) relaxed the 64 mM KCl-induced contraction of the canine basilar artery without affecting the peripheral arteries. These results indicate that VA-045 selectively dilates canine cerebral artery, and that it may be a useful agent for the treatment of cerebrovascular diseases such as stroke.

Electrophysiological effects of monensin, a sodium ionophore,on cardiac

Monensin, a monovalent cation ionophore, transports sodium ions preferentially. We found that, in the cardiac Purkinje fibers, monensin 10(-5) M increased the resting tension of the fiber bundle in Tyrode solution containing 4.5 mM Ca. This ionophore (10(-5) M) shortened the duration of the action potential and suppressed the pacemaker potential. In Na-free or Ca-free solutions, monensin had no effect on the configuration of the action potential. In voltage clamp experiments, monensin 10(-5) M shifted the holding current at -40 mV outwardly, increased the instantaneous inward current (possibly inward rectifying potassium current, IK1) and increased the transient outward current (Ito), whereas it attenuated the hyperpolarization-activated inward current (If). The delayed rectifying outward current (IK) was not significantly affected by monensin 10(-5) M. The transient inward current (ITI) appeared in the presence of monensin 10(-5) M. These changes induced by monensin are consistent with changes in configuration of the action potential induced by monensin. The membrane current changes are considered to be induced by an increase in intracellular Ca concentration, probably via a Na-Ca exchange following an increase in intracellular Na concentration, and by alteration of intra- and extracellular Na and K concentrations.