Barbiturates increase the rate of voltage-dependent inactivation of the calcium current in snail neurones

Effects of barbiturates (thiopentone, pentobarbitone, phenobarbitone and barbitone) on the calcium current (ICa) in identified Helix neurones were studied, using a conventional suction pipette technique. Barbiturates depressed the maximal peak amplitudes (MPA) of ICa in a dose-dependent manner without shifting the current-voltage relationships along the voltage axis. Barbiturates accelerated the decay phase of ICa at high concentrations (1 X 10(-4) to 3 X 10(-3) M), at which concentrations double-pulse experiments showed the increased rate of a voltage-dependent inactivation of ICa. It is concluded that the acceleration of the decay phase of ICa by barbiturates may be due to the increased rate of the voltage-dependent inactivation of ICa.

Neural regulation on the active sodium-potassium transport in hypokalaemic rat skeletal muscles

C.N.S.-induced suppression of muscle Na-pump activity was studied in fast 'twitch' muscle, extensor digitorum longus, of hypokalaemic rats which were fed a K-deficient diet for 0-9 weeks. The results were compared with those of slow 'tonic' muscle, soleus, reported previously. K-deficient diet caused blood hypokalaemia and a considerable K+ loss and Na+ accumulation in the skeletal, heart and smooth muscles. The cellular K+ loss was in the order of soleus greater than extensor digitorum longus greater than diaphragm greater than duodenum greater than auricle greater than ventricle; C.N.S. organs such as cerebrum, cerebellum, medulla oblongata, spinal cord and liver were spared this K+ fall. Skeletal, heart and smooth muscles lost more K+ with prolongation of hypokalaemic periods, whereas plasma K+ concentration did not fall much below 1.6 mM during hypokalaemia. Peripheral nerve section, cervical and brain-stem transection, decerebration and cortical spreading depression with 20% KCl, which activated the active Na+ and K+ transport in soleus muscles during hypokalaemia, could not enhance the pump activity in extensor digitorum longus muscles. Alpha-adrenoreceptor antagonists such as phenoxybenzamine, phentolamine and dibenamine and a specific blocker of post-synaptic alpha 1-adrenoreceptor, prazosin, did not stimulate Na+ and K+ transport in the extensor digitorum longus muscles during hypokalaemia while the beta-adrenoreceptor antagonist, propranolol, also had no effect. The sensitivity of the active Na+ and K+ transport system in rat muscles to ouabain applied intraperitoneally was greater in extensor digitorum longus muscles than in soleus muscles. The binding experiment with a radiolabelled ligand of alpha 1 adrenoreceptor antagonist, [3H]prazosin, demonstrated the presence of alpha 1-adrenergic receptors on the soleus muscle membranes of hypokalaemic rats, but not of normal rats. alpha 1 Adrenergic receptors were not detected on the extensor digitorum longus muscle membranes prepared from either hypokalaemic or normal rats. The correlation between the C.N.S.-induced inhibition on the Na pump in soleus muscle during hypokalaemia and the occurrence of alpha 1 adrenergic receptors on the muscle was discussed.

A dose ranging study of atenolol in hypertension: fall in blood pressure and plasma renin activity, beta-blockade and steady-state pharmacokinetics

The relationship between the oral dosage and plasma concentration of the long-acting cardioselective beta-adrenoceptor blocker atenolol and the antihypertensive response to the the degree of beta-adrenoceptor blockade and change in plasma renin activity (PRA) was evaluated in patients with mild-to-moderate essential hypertension in a double-blind, randomized, between-patient, dose-ranging (25, 50 or 100 mg once daily for 4 weeks) study. The optimum, or minimum, daily dose of atenolol to treat patients with mild-to-moderate hypertension was not clearly identified in this study. A between-treatment comparison did not demonstrate that all blood pressure falls were always less in the 25 mg group than in the other two groups. Calculation of beta-error or the power for the negative results between doses suggested that a large sample size is required to draw a conclusion that no dose-antihypertensive relationship of atenolol exists in the treatment of mild-to-moderate hypertension. A relatively flat plasma concentration-antihypertensive response relationship was observed. Steady-state plasma concentrations of atenolol were dose-related and renal drug clearance was well correlated with individual creatinine clearance. beta-adrenoceptor blockade was better correlated with plasma atenolol concentration. Correlations which were less strong were between plasma drug concentration and change in various blood pressures and between blood pressure falls and beta-adrenoceptor blockade. There was no relationship between the fall in blood pressure and change in PRA. Atenolol appeared to suppress PRA in an all-or-none fashion.

Accelerating effects of pentobarbitone on the inactivation process of the calcium current in Helix neurones

The effect of pentobarbitone on Ca2+ current (ICa), separated from other ionic currents was studied under voltage clamp using a suction pipette technique in Helix neurones. Pentobarbitone depressed the maximal peak amplitude (MPA) of ICa in a concentration-dependent manner without shifting the current-voltage (I-V) relationships along the voltage axis. Increases in external Ca2+-concentration [( Ca2+]o) overcame the inhibitory action of the agent on MPA. Pentobarbitone markedly accelerated the decay phase of ICa which took a distinctly different time course from that of the control. The accelerating action of the agent on the decay phase of ICa was not overcome by increases in [Ca2+]o. In the presence of internal EGTA (20 mM), pentobarbitone also accelerated the decay of ICa. Changes in pH of the external perfusing solution altered the potency of pentobarbitone in depressing MPA; in the presence of pentobarbitone (3 X 10(-4) M) at pH of 7.0, 8.0 and 9.0, fractional inhibition was approx. 46%, 21% and 4%, respectively. Internal application of pentobarbitone (10(-4)-10(-3) M) inhibited MPA, but exerted no effect on the decay phase of ICa. Pentobarbitone (10(-4) M) markedly accelerated the decrease of MPA of ICa induced by repetitive stimuli applied at an interval of 150 ms, indicating a use-dependent depression of MPA. Results provide evidence that pentobarbitone has a dual action on ICa, inhibiting MPA and accelerating the decay phase of ICa.

Actions of calcium antagonists on calcium currents in Helix neurons. Specificity and potency

We have examined the effects of organic Ca++ channel blockade on calcium currents in Helix neurones, using a suction pipette technique which allows internal perfusion of the cell body and voltage clamp. In experiments on large cells with large currents, a microelectrode was used to measure membrane potential and provide the feedback potential for the voltage clamp. Calcium current was recorded after suppression of Na+ and K+ currents. The Ca++ conductance transports Ca++ and other divalent cations, such as Sr++, Ba++, Mn++, Zn++ and Cd++. Calcium current is temperature-dependent, and the Q10 of peak current was about 2.5. The organic Ca++ antagonists, verapamil, diltiazem, and nifedipine, inhibit calcium currents over the entire range of the current-voltage relationship. The effects are dose-dependent and there is no shifting in the current-voltage curves. Increases in extracellular Ca++ overcame the inhibitory action of the agents. Double reciprocal plots for peak calcium currents vs. external Ca++ concentrations in the presence or absence of diltiazem indicated competition with Ca++ at a common binding site. Intracellular application of diltiazem inhibited calcium currents.

Quantitative in vivo studies on the active Na-K transports in "tonic" muscle of the hypokalemic rat

Central nervous system (CNS)-induced suppression on the muscle Na-pump activity was studied in soleus (SOL) muscles of hypokalemic rats. Peripheral nerve section, cervical soleus and brainstem transection, decerebration, and cortical spreading depression with 20% KCl activated the Na-pump in SOL muscles during hypokalemia. Blockage of the nerve conduction by tetrodotoxin (TTX) also activated the Na-pump in SOL muscles. The activation of Na-pump after the denervation was completely abolished by the pre-treatment of ouabain. However, the muscle cation contents were not affected by the injection of curare and atropine. The activation of Na-pump in the muscles after denervation in the curarized hypokalemic rats was completely removed by electrical stimulus of the distal nerve stump of cut sciatic nerve. alpha-Adrenoreceptor antagonists (phenoxybenzamine, phentolamine and dibenamine, and prazosin) stimulated the Na+ and K+ transports in the SOL muscles during hypokalemia while beta-adrenoreceptor antagonist (propranolol) had no effect. The denervation effect on SOL muscle cation contents was not affected with or without the presence of propranolol. It is concluded that CNS acts to inhibit the Na-pump mechanism in SOL muscles of hypokalemic rats and the inhibition is achieved by the apparent release of catecholamines onto muscle following neural activity. Thus, the CNS-induced suppression on the muscle Na-pump is prevented by denervation and by treatment with drugs that block either nerve conduction or alpha-adrenoreceptor.

Further analysis of inhibitory effects of propranolol and local anaesthetics on the calcium current in Helix neurones

1 The effects of propranolol and local anaesthetics on Ca2+ current (Ica), individually separated from other ionic currents, in Helix neurones were studied under voltage clamp, using a suction pipette technique. 2 Increases in external Ca2+ concentrations overcame the inhibitory action of propranolol on Ica. Double reciprocal plots for peak Ica versus external Ca2+ concentrations in the presence or absence of propranolol did not intersect at the ordinate. 3 Internal application of propranolol (10-4M) inhibited Ica to about 40-60% of the control in a time-dependent manner. 4 Lignocaine and procaine at concentrations of 10-3-10-2 M inhibited Ica without shifting the threshold in the I-V relationships. Internal application of lignocaine (10-3-10-2M) also inhibited Ica: the ratio of depression of the Ica was almost equivalent to that of the agent applied externally. 5 The results provide evidence that propranolol inhibits Ica in the noncompetitive manner with Ca2+ at the cell membrane, and suggest that the agents may occupy the receptor site in the Ca2+-channel somewhere between the outer surface and inner phase of the membrane.

[Gestational changes of cytoplasmic and nuclear estrogen and progesterone receptors in the human myometrium (author's transl)]

The gestational changes of both cytosol and nuclear estrogen and progesterone specific binding sites in human myometrial were studied to evaluate the role of these steroids in the mechanism of initiating labor. 1) In nonpregnant women, early and term pregnancy, the dissociation constants (Kd) of cytosol estradiol-17 beta (ERc) and progesterone (PRc) showed no change but the number of binding sites (NBS) of the former varied from 275 +/- 1.3 to 5.5 +/- 0.1 and 10.0 +/- 2.0 (x 10(-15) mol/mg protein) and the latter from 2.5 +/- 0.5 to 25.5 +/- 3.2 to 3.8 +/- 0.8, respectively. The number of nuclear acceptor sites of estradiol-17 beta (EAn) changes during this period from 4.0 +/- 1.5 to 5.0 +/- 1.0 and 0.6 +/- 0.3 (x 10(-15) mol/g DNA), while those of progesterone (PAn) are from 1.3 +/- 0.3 to 1.2 +/- 0.5 and 0.3 +/- 0.1, both showing a significant decrease towards term. 2) After the onset of labor, the nuclear acceptor sites increased significantly (RAn: 0.6 +/- 0.3/4.3 +/- 1.0, PAn: 0.3 +/- 0.1/3.3 +/- 0.8 x 10(-15) mol/micrograms DNA, p less than 0.01), while those in the cytosol remained unchanged. 3) Te ERc/PRc ratio of Kd unchanged throughout pregnancy but that of NBS increased a term (p less than 0.01) and the ratio of EAn/PAn decreased (p less than 0.05). This change became more apparent after the onset of labor. These findings suggest that at term, the myometrial hormone environment becomes dominant and this intracellular change of hormone sensitivity play an important role in the mechanism of initiating human parturition.

Inhibitory effects of propranolol on the calcium current of Helix neurones

1 Calcium current (ICa) and potassium current (IK) in isolated nerve cell bodies of Helix aspersa were independently separated after suppression of Na+ and K+ currents, and Na+ and Ca2+ currents, respectively. The suction pipette method was used. Under voltage clamp conditions, the effects of propranolol on both the ICa and IK were examined. 2 Propranolol inhibits the ICa at relatively low concentrations (10(-6)-10(-5) M). The inhibitory action was dose-dependent. 3 The IK was moderately suppressed by the drug at high concentrations (10(-5)-5 X 10(-1) M). 4 Results provide evidence for a new aspect of the pharmacological action of propranolol on the excitable cell membrane.

[Study of oxytocin receptor activities in human myometrial preparation (author's transl)]

This study was designed to investigate the oxytocin (OT) receptor activities in the human myometrial specimen throughout the course of pregnancy and in labor. The 3H-labeled OT with adequate specific activity (24 Ci/mM) and biologic activity (350 IU/mg) was employed for the OT radioreceptor assay and the apparent dissociation constant (Kds) and the number of binding sites (NBS) were analyzed by Scatchard plot. These activities were predominantly found in 20,000 xg pellets of the myometrial specimens and its binding activities were 2.2 +/- 0.1 nmol/mg protein that were assessed to be composed of two binding fractions: High-affinity--low capacity receptor fraction and low affinity--high capacity fraction. The gestational increase of the binding affinity was significant and so was the increase of the capacity, and the Kd was 1.87 +/- 0.30 nM and the NBS was 1.50 +/- 0.50 pmol/mg protein in the full term specimens and both were significantly higher than those of the nonpregnant specimens (p less than 0.01). When active labor was initiated, a significant decrease of the binding capacity (0.74 +/- 0.21 pmol/mg protein) was found, regardless of the mode of onset of labor; i.e. spontaneous or induced labor, while the binding affinity remained unchanged. These findings suggest that the gestational increase of the uterine sensitivity to OT is due to the increase of both binding affinity and capacity of the OT receptors. And there are OT and OT receptor interaction actively involved during the active stage of labor and this interaction seems to be coupled with the contractile process but is apparently modified when active labor had been already initiated.

[Electrophysiologic effects of calcium channel blocking agents on the sinus node function in anesthetized dogs (author's transl)]

The electrophysiologic effects of calcium channel blocking agents, diltiazem, verapamil and nifedipine, on the sinus node function were examined in 43 anesthetized closed-chest dogs in comparison with the effects of propranolol. The parameters of sinus node function, i.e. sinus cycle length (SCL), sinus node recovery time determined by overdrive suppression (SRT), both of which are thought to reflect sinus node automaticity, and sinoatrial conduction time estimated by Strauss method (SACT), were evaluated. Intravenously administered diltiazem (0.2 mg/kg), verapamil (0.1 mg/kg) and propranolol (0.1 approximately 0.2 mg/kg) increased SCL and SRT significantly although the increase of these parameters induced by nifedipine (0.03 mg/kg) was not statistically significant. The calcium channel blocking agents did not significantly affect SACT in contrast with propranolol which showed a prolonging effect. Thus calcium channel blocking agents suppressed sinus node automaticity yet had little effect on sinoatrial conduction.

Type A alternating Wenckebach periodicity in the re-entrant path of ventricular extrasystoles

A patient with ventricular extrasystoles is reported in whom Type A alternating Wenckebach periodicity in the re-entrant path of the extrasystoles is suggested for the first time. Namely, it appears that 2:1 exit block occurs at a proximal level in the re-entrant path and block of the Wenckebach form occurs at a distal level in the path. The presence of three-level block in the re-entrant path is also suggested in this patient.

Study of oxytocin receptor in human myometrium using highly specific 3H-labeled oxytocin

A highly specific tritium labeled oxytocin (3H-OT) was synthesized utilizing the method of catalytic substitution of halogen for hydrogen. The specific activity of 3H-OT was 19 Ci/mM and the biologic activity was 350 U/mg, which was sufficient for the OT radioreceptor assay. The maximum % uptake of 3H-OT in the human myometrium was observed in 20,000 X g pellets under the optimal conditions of pH 7.4, at 20 degrees C and the incubation time of 90 min and it was augmented in the presence of Mn++. It was observed from the Scatchard plot, that the binding site of OT in the human myometrial specimens was a single type within the range of OT concentration of 0.4 nM to 1.6 nM. The dissociation constants (Kd) and the number of binding sites (NBS) showed a relative increase as gestation advance. The apparent Kd of term pregnancies was 1.25 X 10(-9) M regardless of the presence or absence of labor pains, while the NBS of term pregnancies with and without labor pain was 1.2 X 10(-12) and 4.7 X 10(-12) moles/mg, protein, respectively.

The effects of diltiazem hydrochloride on the cardiac conduction: a clinical study of His bundle electrogram

The effects of diltiazem hydrochloride, a new Ca++ antagonistic antianginal drug, on the cardiac conductivity were evaluted in 10 patients with atherosclerotic heart disease. His bundle electrograms were obtained by catheter technique. R-R, A-H and H-V intervals were measured before and after intravenous administration of diltiazem. Diltiazem acted towards significant prolongation in A-H interval. R-R and H-V intervals were insensitive to diltiazem. Diltiazem did not interrupt the cardiac effects of atropine when A-H prolongation was still observed in the subject pretreated with atropine. In short, diltiazem depresses the conductivity of the atrioventricular node selectively and this is not mediated through vagus tone change. This Ca++ antagonist induced A-H prolongation strongly suggests the contribution of Ca++ current on the generation of atrioventricular nodal action potential in humans.

Clinical pharmacologic observations on timolol. I. Disposition and effect in relation to plasma level in normal individuals

The disposition profiles of a new beta-adrenergic blocking drug, timolol, were investigated at 11 different times in normal individuals after a single oral dose. The disposition of timolol follows first-order kinetics and may be adequately described by a one-compartment model. The pharmacokinetic data were not significantly different among the three dose levels examined. After the single oral doses, overall elimination half-life was 3.2 +/- 0.2 hours (mean +/- S.E.M.), with an observed peak time of 2.0 +/- 0.2 hours; extrapolated volume of distribution was 1.81 +/- 0.15 liter/kg; and the total plasma clearance was 557 +/- 61 ml/min. Approximately 20 per cent of elimination from the human body was dependent on the kidney. The area under the curve from zero to infinity and the peak concentration observed were dose dependent. A linear relationship was found between timolol plasma concentrations and beta-adrenergic blocking effects (per cent inhibition), as estimated from exercise-induced tachycardia. Timolol is a beta blocker which must await further clinical trials for the assessment of therapeutic implications in relation to plasma levels.

Clinical pharmacologic observations on timolol. II. Antihypertensive effect and kinetic disposition on twice-daily dosing in patients with mild or moderate hypertension

Timolol given on a twice-daily schedule has shown both antihypertensive effectiveness and plasma renin-suppressing action in eight patients with mild or moderate hypertension. However, the causal relationship between the drug plasma level, blood pressure fall, and change in plasma renin activity was not so clearly demonstrated in the present study. The disposition profiles of timolol at the steady state show an elimination half-life of 4.7 +/- 0.7 hours and a total plasma clearance of 225 +/- 21 ml/min. These values are found to be different from those of our previous observations obtained in normal individuals. Although the range of mean timolol concentrations at steady state varies to a certain extent among different patients, the dosage regimens for patients who will receive treatment for certain chronic disease states (e.g., arrythmias, obstructive cardiomyopathy, and angina pectoris, but not hypertension) in relation to plasma levels should be based on the disposition data obtained under steady state conditions. Bronchospasm developed in one of eight patients whose timolol level was found to be higher than the average of other patients given the same dosage.