Kumiko Shibasaki

The role of extracellular Ca2+ in carbachol-induced tonic contraction of the pig detrusor smooth muscle

The role of extracellular Ca2+ in the toniccontractile response to muscarinic receptor stimulation was investigated in isolated detrusor smooth muscle from the pig urinary bladder.Carbachol (10−8 −10−5 M) produced a concentration-dependent contractile response in isolated pig detrusor smooth muscle strips consisting of an initial phasic component followed by a tonic component. During the plateau of the tonic contractions induced by carbachol at the submaximal concentration of 10−6 M, the inhibiting effects of atropine, EGTA, nifedipine (a voltage-dependent calcium channel antagonist), H-7 [a protein kinase C (PKC) inhibitor] and YM 934 (a potassium channel opener) on the contractions were evaluated. Atropine (10−10 −3 × 10−8 M) concentration-dependently inhibited the tonic contractions induced by carbachol. In the same experimental conditions, EGTA (4 mM) and nifedipine (10−9 −3 × 10−7 M) depressed the tonic contractions in a concentration-dependent manner as did H-7 (10−5 −3 × 10−5 M) and YM934 (10−8 -10−6 M). However, H-7 (10−5-3 × 10−5 M) and YM934 (10−6 M) were very weak in inhibiting the contractions induced by KCl (50 mM) in isolated pig detrusor smooth muscle strips.These results suggest that the tonic-contractile response induced by carbachol in pig detrusor smooth muscle strips is dependent mainly on depolarization of the cell membranes and an influx of extracellular Ca2+, and also suggest that this depolarizing response may be due to inactivation of ATP-sensitive potassium channels through muscarinic activation of PKC.

Effect of the Potassium Channel Opener YM934 on the Contractile Response to Electrical Field Stimulation in Pig Detrusor Smooth Muscle

PURPOSE The effect of a potassium channel opener, YM934, on the contractile response to excitatory neurotransmitters was investigated in isolated pig detrusor smooth muscle. MATERIALS AND METHODS Electrical field stimulation (EFS; 5 second trains, 50 V, 0.8 msec. duration), alpha, beta-MeATP (3 x 10(-7) to 10(-5) M.) or carbachol (3 x 10(-8) to 10(-6) M.) produced a contractile response in isolated pig detrusor smooth muscle. The effect of YM934 on the contractile responses was evaluated in comparison with the antagonism of the putative cotransmitters, acetylcholine and ATP. RESULTS A tetrodotoxin-sensitive, frequency-dependent contractile response to electrical field stimulation was obtained. Atropine (3 x 10(-8) M.) significantly inhibited the contractile response at high frequencies, whereas alpha, beta-MeATP (5 x 10(-6) M.) (desensitizer of P2X-purinoceptors) significantly inhibited the response at low frequencies. YM934 (10(-8) to 10(-7) M.) dose-dependently inhibited the nerve-mediated contractile responses to all frequencies but preferentially at low frequencies, by analogy with alpha, beta-MeATP. A combination of YM934 (3 x 10(-8) M.) and atropine (3 x 10(-8) M.) reduced the response at all frequencies to between 10 and 20% of control, an effect similar to that obtained with alpha, beta-MeATP (5 x 10(-6) M.) and atropine (3 x 10(-8) M.). In addition, YM934 (3 x 10(-8) M.) markedly inhibited the contractile response induced by exogenously applied alpha, beta-MeATP (3 x 10(-7) to 10(-5) M.) but only slightly inhibited the contractile response induced by exogenously applied carbachol (3 x 10(-8) to 10(-6) M.). CONCLUSION These results suggest that YM934 may hyperpolarize the membrane of pig detrusor smooth muscle through the opening of ATP-sensitive potassium channels and, as a result, may functionally inhibit the contractile response to purinergic nerve stimulation that elicits the membrane depolarization.

Inhibitory effects of a selective endothelin-A receptor antagonist YM598 on endothelin-1-induced potentiation of nociception in formalin-induced and prostate cancer-induced pain models in mice.

In some diseases in which endothelin-1 (ET-1) production increases (e.g. prostate cancer), ET-1 is considered to be involved in the generation of pain. In the present study, we investigated the effects of a selective endothelin-A receptor antagonist, YM598, on the nociception potentiated by ET-1 in formalin-induced and cancer inoculation-induced pain models in mice. The formalin-induced pain model was prepared by intraplantar injection of 0.7% formalin into the hind paws of ICR mice, and the cancer pain model was prepared by inoculation of the human prostate cancer cell line PPC-1 into the hind paws of severe combined immunodeficiency mice. Formalin caused a biphasic pain response and paw edema in the mouse hind paw. ET-1 (10 pmol/paw) potentiated these responses, and single oral administration of YM598 (0.3-3 mg/kg) significantly inhibited this ET-1-induced potentiation of nociception and paw edema. ET-1 (10 pmol/paw) also potentiated the pain response in prostate cancer-inoculated mice. Both YM598 and atrasentan (0.3-3 mg/kg) significantly inhibited the ET-1-induced potentiation of nociception. These results suggest that selective endothelin-A receptor antagonists relieve pain in patients with various diseases in which ET-1 production increases (e.g. prostate cancer).

Pharmacologic Profiles of Ym934, a Novel Potassium Channel Opener

Pharmacologic profiles of YM934, a newly synthesized 1,4-benzoxazin derivative K channel opener were evaluated in in vitro and in vivo experiments. In isolated rat portal vein, YM934 and a benzopyran derivative K channel opener lemakalim inhibited the frequency of spontaneous rhythmic contractions concentration de-pendently, with IC50 values of 14 and 38 μM, respectively. These inhibitory effects were competitively antagonized by glibenclamide (an ATP-sensitive K channel blocker; 10-7-3 x 10-6 M). In isolated rabbit aorta, YM934 (10-8-10-6 M) and lemakalim (10-8-l0-6 M) relaxed the contractions induced by 20 mAf KC1 concentration dependency but were ineffective against the contractions induced by 50 mM KC1. YM934 (10_8-3 x KT6 M) and lemakalim (3 x 10-8-10-5 M), but not the calcium antagonist nifedipine, relaxed the contractions induced by norepinephrine (NE 10-6 M) or prostaglandin F2α (PGF2α 3 x 10_6 M) in the aorta. In pentobarbital-anesthetized dogs, YM934 (1–10 μg/kg intravenously, i.v.) dose-dependently increased coronary artery blood flow (CBF), and decreased total peripheral resistance (TPR) and mean blood pressure (MBP). YM934 selectively increased CBF, but had little effect on vertebral, carotid, mesenteric, renal and femoral artery BF. These vasodilatory effects of YM934 were antagonized by glibenclamide. YM934 is a potent K channel opener and possesses potent vasodilatory effects, with particularly pronounced effects on the coronary artery. These effects of YM934 may, like lemakalim, be mediated by opening of ATP-sensitive K channels.

Antianginal effects of YM-16151-4 in various experimental angina models

The antianginal effects of YM-16151–4, a combined calcium entry blocking and β1-adrenoceptor blocking agent, were evaluated in various experimental angina models and compared with those of nifedipine and propranolol. In anesthetized dogs, YM-16151–4 (0.3 and 1 mg/kg intravenously, i.v.) increased coronary blood flow and reduced myocardial oxygen consumption (MV02). In isolated dog coronary arteries, YM-16151–4 concentration-dependently inhibited 3,4-diaminopyridine-induced rhythmic contractions with an IC50 value of 91 nAf. In anesthetized rats, YM-16151–4 also inhibited the ST-segment depression induced by vasopressin (0.5 U/kg i.v.) with an ED50 value of 29 mg/kg orally, (p.o.). Nifedipine was also effective in these models, but propranolol was not. In addition, YM-16151–4 (0.3 mg/kg i.v.) inhibited the ST-segment elevation in the epicardial ECG induced by coronary artery occlusion in anesthetized dogs. Propranolol (1 mg/kg i.v.) also inhibited this elevation, but nifedipine (0.003 mg/kg i.v.) did not. In anesthetized dogs, furthermore, the prolongation of PQ-interval induced by YM-16151–4 was almost the same as that induced by propranolol. These results demonstrate that YM-16151–4, in contrast to nifedipine and propranolol, is fully effective in these various types of angina models. Thus, YM-16151–4 is expected to prove a valuable antianginal agent in treatment of various types of angina pectoris, with these antianginal effects resulting from the sum of its calcium entry blocking and (β1-adrenoceptor blocking activities.

Antianginal Effects of YM430, a Novel Calcium Entry–Blocking and β-Adrenoceptor–Blocking Agent in Several Experimental Angina Models

1. We evaluated the antianginal effects of YM430 in several experimental models in vitro and in vivo. 2. In isolated dog coronary artery, YM430 (10(-8)-10(-6) M) inhibited 3,4-diaminopyridine-induced rhythmic contractions with an IC50 value of 59.2 nM. 3. In anesthetized rats, YM430 (10-100 mg/kg PO) inhibited arginine vasopressin-induced ST-segment depression with an IC50 value of 36.6 mg/kg PO. 4. In anesthetized dogs, YM430 (0.3 mg/kg IV) significantly inhibited ST-segment elevation induced by coronary artery occlusion. 5. These findings suggest that YM430 may be of value in the treatment of various types of angina pectoris such as variant and stable angina.

Cardiovascular effects of YM-16151-4 : a novel calcium entry blocking and selective β1-adrenoceptor blocking agent in rats and dogs

Summary: The cardiovascular effects of YM-16151–4 were evaluated in rats and dogs. In conscious rats, YM-16151–4 (3–30 mg/kg p.o.) produced a dose-dependent hypotensive effect without increasing heart rate (HR) and plasma renin activity (PRA). Nifedipine (3–10 mg/kg p.o.) produced a dose-dependent hypotensive effect but significantly increased HR and PRA. Atenolol (30 mg/kg p.o.) decreased PRA but did not decrease blood pressure and HR. The cardiovascular effects of the combination of nifedipine and atenolol were similar to those of YM-16151–4. It is interesting that the time course of the hypotensive effect of YM-16151–4 was similar to that of its β1-adrenoceptor blocking effect, although the time courses of these effects of the combination of nifedipine and atenolol were different. In conscious dogs, YM-16151–4 (0.3–10 mg/kg p.o.) also produced a long-lasting hypotensive effect with almost no effect on HR and PQ-interval. The time course of the β1-adrenoceptor blocking effect was similar to that of its hypotensive effect. Furthermore, during 10-day repeated oral administration, neither tolerance nor augmentation was observed in the hypotensive and β1-adrenoceptor-blocking effects. In conclusion, the present results indicate that YM-16151–4 is an effective and long-lasting hypotensive agent that does not increase HR and PRA. These effects of YM-16151–4 may be attributable to its calcium-entry-blocking and β1-adrenoceptor-blocking activities, and the ratio of two activities was constant after single and repeated oral administrations.

Cardiovascular effects of a novel calcium entry blocking and selective beta 1-adrenoceptor blocking agent, YM-16151-4, in anesthetized and conscious dogs.

Cardiovascular effects of YM-16151-4, a combined calcium entry blocking and beta 1-adrenoceptor blocking agent, were evaluated in dogs. In anesthetized dogs, YM-16151-4 (0.01-1 mg/kg intravenously, i.v.) dose-dependently increased coronary blood flow (CBF) and decreased mean blood pressure (MBP), total peripheral resistance (TPR), dP/dtmax, double product, and left ventricular (LV) work without increasing heart rate (HR) and cardiac output (CO). YM-16151-4 increased vertebral blood flow as well as CBF, but had no effect on carotid, mesenteric, renal, and femoral blood flow. Coronary vasodilating activity of YM-16151-4 was also observed after intracoronary artery injection (i.a.). In anesthetized and vagotomized dogs, YM-16151-4 dose-dependently inhibited isoproterenol (0.2 micrograms/kg i.v.)-induced tachycardia and decrease in diastolic BP (DBP), with ED50 values of 0.039 and 0.52 mg/kg i.v., respectively. In conscious dogs, YM-16151-4 (0.1-1 mg/kg i.v.) produced a dose-dependent hypotensive effect with no effect on HR or PQ-interval. The hypotensive effect of YM-16151-4 (0.3 and 1 mg/kg i.v.) reached its maximum approximately 1-2 h after each dosing and lasted 6-8 h. These results suggest that YM-16151-4 actually behaves as a hybrid compound, combining calcium entry blocking and beta 1-adrenoceptor blocking activities, and that this compound could be a novel long-acting antianginal and antihypertensive agent.

Pharmacological properties of YM-26365, a low molecular weight, orally active renin inhibitor.

This report describes the pharmacological properties of a novel renin inhibitor (YM-26365: (3R)-3-[3-[(1S)-1-cyclohexylmethyl-2-hydroxy-3- [(1-methyl-5-tetrazolyl)thio]propyl]ureido]-1-methyl-5-phenyl- 2,3-dihydro-1H-1,4-benzodiazepin-2-one) with molecular weight 577 and no peptide bonds. YM-26365 inhibited human plasma renin with an IC50 value of 2.9 x 10(-6) M, but did not affect plasma renin from dogs, rabbits, and rats at 10(-4) M. YM-26365 inhibited not only human renin, but also cathepsin D with an IC50 value of 1.7 x 10(-5) M. This compound competitively inhibited the reaction between recombinant human renin and N-acetyl tetradecapeptide with a Ki value of 1.1 x 10(-6) M. In pithed spontaneously hypertensive rats, YM-26365 at 10 mg/kg i.v. significantly antagonized the pressor response to recombinant human renin, but did not affect responses to angiotensin II, angiotensin I, norepinephrine, or arginine vasopressin. Similarly, oral administration of YM-26365 (10 and 30 mg/kg) to pithed spontaneously hypertensive rats caused a shift to the right of the recombinant human renin dose-pressor response curve. Systemic bioavailability as determined on the basis of the ratio of the total area under the plasma concentration-time curve after 3 mg/kg i.v. and 30 mg/kg orally to rats was 9.6%. These results demonstrate that YM-26365 is a weak but orally absorbed, low molecular weight renin inhibitor.