Effects of alfentanil on isolated cardiac tissues of the rabbit

Alfentanil causes cardiac stimulation or depression in intact animals and in clinical practice; there is no information concerning its direct effects on the heart. Therefore, we studied the effects of alfentanil on isolated cardiac tissues from young adult rabbits. The right atrium with sinoatrial node (SA node) was beating spontaneously, and the left atrium and papillary muscle were stimulated. Isometric contraction was monitored. Alfentanil, in concentrations of 0.05-0.5 mM, decreased by 6%-55% the frequency of contractions of the right atrial-SA node in a dose-related manner. In left atria and right atrial-SA node, but not in papillary muscle, alfentanil in concentrations greater than or equal to 0.01 mM increased the peak developed force and its maximum rate of increase. The time-to-peak developed force was prolonged in papillary muscle but not in right atrial-SA node and left atria. The maximum rate of fall of peak developed force was increased in left atria and decreased in papillary muscle by the administration of alfentanil. The time-to-50% relaxation of peak developed force was not consistently affected by alfentanil in all three muscle preparations. The same concentrations of alfentanil (greater than or equal to 0.01 mM) increased resting force in papillary muscle but not in left atria or right atrial-SA node. It is concluded that alfentanil has direct positive inotropic and negative chronotropic effects on the heart and that it causes contracture of ventricular myocardium.

[Antagonism of verapamil on the injurious action of endothelin of isolated rat heart]

Isolated rat hearts perfused with endothelin at a concentration of 10(-8) mol/L showed serious functional and cellular myocardial deterioration as manifested by a significant increase of mean perfusion and left ventricular pressure, decrease of +/- LV dp/dtmax, leakage of myocardial protein, formation of lipid peroxides, increase of myocardial calcium content, etc. Calcium channel blocker, verapamil, effectively antagonized the injurious action of endothelin on rat heart whether administered along with or after endothelin perfusion.

Genetic and molecular analysis of the SOE1 gene: a tRNA(3Glu) missense suppressor of yeast cdc8 mutations

The CDC8 gene of Saccharomyces cerevisiae encodes deoxythymidylate (dTMP) kinase and is required for nuclear and mitochondrial DNA replication in both the mitotic and meiotic cell cycles. All cdc8 temperature-sensitive mutants are partially defective in meiotic and mitochondrial functions at the permissive temperature. In a study of revertants of temperature-sensitive cdc8 mutants, the SOE201 and SOE1 mutants were isolated. The SOE201 mutant is a disome of chromosome X to which the cdc8 gene maps. Using the chromosome X aneuploids to vary cdc8 gene dosage, we demonstrate that different levels of dTMP kinase activity are required for mitotic, meiotic or mitochondrial DNA replication. The SOE1 mutant contains a dominant suppressor that suppresses five different cdc8 alleles but does not suppress a complete cdc8 deletion. The SOE1 gene is located less than 1.5 cM from the CYH2 gene on chromosome VII and is adjacent to the TSM437-CYH2 region, with the gene order being SOE1-TSM437-CYH2. SOE1 is an inefficient suppressor that can neither suppress the cdc8 hypomorphic phenotype nor restore dTMP kinase activity in vitro. SOE1 is a single C to T mutation in the anticodon of a tRNA(3Glu) gene and thereby, produces a missense suppressor tRNA capable of recognizing AAA lysine codons. We propose that the resultant lysine to glutamate change stabilizes thermo-labile dTMP kinase molecules in the cell.

[Factors affect Na(+)-Ca2+ exchange in rat's cardiomyocytes and protein-reconstituted liposomes]

Rat's Ca-resistant ventricular myocytes and reconstituted liposomes of canine cardiac sarcolemma were used in analysing factors affecting Na(+)-Ca2+ exchange system. Decrease in extracellular (extravesicular) Na+ or increase in intracellular Na+ by inhibition of the Za(+)-K(+)-ATPase with ouabain stimulated the Na(+)-Ca2+ exchange. Mn2+, an antagonist of Na(+)-Ca2+ exchange, dose-dependently inhibited the Na(+)-dependent Ca2+ uptake. However, verapamil had no effect on it. Arachidonic acid and lipid peroxides caused by incubation with-H2O2 significantly stimulated Na(+)-Ca2+ exchange in a dose-dependent fashion.

[Significance of endothelin in shock pathogenesis]

Endothelin is a recently discovered bioactive peptide produced by vascular endothelial cells. By means of specific radioimmunoassay we found that plasma endothelin level in patients with late septic shock was significantly increased. And a typical shock model in healthy rats was reproduced by continuous infusion of endothelin (endothelin shock). Infusion of endothelin at a small dose to hemorrhagic shocked rats deteriorated the shock process and resulted in an irreversible development. From these results it is suggested that endothelin may be an endogenous injury-inducing factor, acting as one of the important humoral factors involved in shock pathogenesis.

Intracellular mechanisms of halothane's effect on isolated aortic strips of the rabbit

The intracellular mechanisms of halothane action were examined in vascular smooth muscle from the aorta. Medial layers of the aorta from rabbits were mounted on photodiode tension transducers, stretched to 20 mg resting tension, and "skinned" with saponin. The skinned fiber preparations were then immersed in bathing solutions to study the effects of halothane (0.5-2%) on Ca2+ activation of the contractile proteins, and Ca2+ uptake and release from the sarcoplasmic reticulum (SR) using caffeine-induced tension transients. For comparison, isolated intact aortic rings were mounted on Blinks' dual tissue bath and attached to force transducers. The preparations were contracted with either 40 mM KCl, or norepinephrine (NE) followed by acetylcholine (ACh)- or sodium nitroprusside (SNP)-induced relaxation. At steady state contraction or relaxation, the effects of halothane (1-3%) were studied. The steady state tension during halothane was expressed as a percentage of the steady state tension before administration of halothane. In the isolated intact aortic rings, halothane (1-3%) produced biphasic effects on KCl-induced tension, i.e., an initially slight increase followed by decreases, independent of endothelium. Halothane markedly increased tension in the ACh- or SNP-relaxed state. The effects were dose-dependent. In the skinned aortic strips, halothane slightly decreased maximum Ca2+-activated tension development of the contractile proteins. Halothane decreased Ca2+ accumulation in the SR and increased Ca2+ release from the SR in a dose-dependent manner. The halothane-induced increases in Ca2+ release from the SR were blocked by ryanodine, an SR Ca2+ release channel blocker. It is concluded that halothane directly causes vascular contraction or relaxation, depending on the condition, and that halothane's effects on the SR may play a role.

Comparison of the effects of halothane on skinned myocardial fibers from newborn and adult rabbit: II. Effects on sarcoplasmic reticulum

The effect of halothane on Ca2+ uptake or release by the sarcoplasmic reticulum (SR) was compared in the newborn and adult rabbit myocardium. The sarcolemma of right ventricular myocardium was disrupted (skinned) by homogenization. Fiber bundles were dissected from the homogenate, mounted on tension transducers, and immersed sequentially in five solutions that loaded Ca2+ into the SR, then in solutions containing either 2 or 25 mM caffeine to release SR-stored Ca2+, resulting in transient tension development. Experimental solutions were saturated with halothane in N2 gas during Ca2+ uptake by SR, Ca2+ release by SR, or during both SR Ca2+ uptake and release. Halothane (0.5-1.7%) resulted in dose-dependent depression of SR Ca2+ uptake in both newborn and adult skinned fibers. Less tension transient depression resulted in newborn (35%) than adult skinned fibers (49.5%, P less than 0.05) with 0.5% halothane exposure during SR Ca2+ uptake. Similar depression resulted in newborn (53.7% and 73.4%) and adult fibers (65.2% and 77.9%) with 1.0% and 1.7% halothane. Halothane had little effect on SR Ca2+ release by 25 mM caffeine but enhanced submaximal SR Ca2+ release by 2 mM caffeine more in newborn than adult myocardium. Increased Ca2+ efflux from newborn SR may contribute to the greater sensitivity of intact newborn cardiac muscle to exposure to halothane.

[Anoxia-reoxygenation injury in isolated rat myocytes is modulated by cell sodium during the anoxia period]

Using the model of anoxia-reoxygenation injury in isolated rat myocytes, we observed that incubation of myocytes with ouabain, inhibitor of Na+-K+ ATPase, during anoxia period significantly increased the cell sodium content. These myocytes demonstrated severe injury and intracellular calcium overload during reoxygenation period. The sodium content of myocytes at the end of anoxia period was positively correlated with the overload of intracellular calcium at reoxygenation (r = 0.882, P less than 0.01). Mn2+, an inhibitor of Na+-Ca2+ exchange, significantly attenuated the anoxia-reoxygenation injury when given during reoxygenation period. Mn2+ also inhibited the cell injury caused by incubation of myocytes with Na+-free medium. These results suggest that anoxia-reoxygenation injury of rat myocytes is modulated by cell sodium during the anoxia period, and the Na+-Ca2+ exchange mechanism plays an important role in influx of extracellular calcium during reoxygenation period.

Comparison of the effects of halothane on skinned myocardial fibers from newborn and adult rabbit. I. Effects on contractile proteins

The effect of halothane on maximal and submaximal Ca2+-activated tension development of the contractile proteins of newborn and adult cardiac muscle from rabbits was determined. Right ventricular muscle was removed from newborn and adult rabbits, and the sarcolemma was disrupted (skinned) by homogenization. Fiber bundles were dissected from the homogenate and mounted on tension transducers. Fiber bundles were alternately immersed in relaxing solution [( Ca2+] less than 10(-9) M) and contracting solutions (various [Ca2+] from 10(-5.6) to 10(-3.8) M), which were saturated with 100% N2 alone or with three concentrations of halothane-N2 mixture. In the absence of halothane, newborn skinned myocardial fibers were slightly more sensitive to submaximal Ca2+ concentrations than were adult myocardial fibers. [Ca2+] required for 50% maximum tension were 10(-5.43) M and 10(-5.31) M, respectively (P less than 0.05). Halothane (1-3%) decreased the maximal Ca2+-activated tension (at [Ca2+] = 10(-3.8) M) similarly in adult and newborn myocardial fibers in a dose-dependent fashion. Tension was reduced by 5.9% for each 1% increase in halothane concentration. Halothane also decreased the sensitivity of adult myocardial skinned fibers to submaximal Ca2+ concentrations (10(-5.6) M to 10(-5.0) M) by shifting the Ca2+-tension response curve to the right. Only 3% halothane decreased the sensitivity of newborn myocardial skinned fibers to Ca2+. The authors conclude that halothane causes less depression of Ca2+ activation of the contractile proteins in newborn than adult rabbit myocardium and that this effect of halothane cannot account for greater negative inotropy of halothane in the newborn.

Intracellular mechanisms of verapamil and diltiazem action on striated muscle of the rabbit

Skinned fibers from striated muscle were used to study the intracellular mechanisms (contractile proteins and sarcoplasmic reticulum [SR]) of action of diltiazem (DT) and verapamil (VP) on muscle contraction. Rabbit papillary muscle (PM), and the skeletal muscles adductor magnus (AM, fast-twitch) and soleus (SL, slow-twitch) were used. The muscles were skinned by homogenization and fibre bundles for PM and single fibres for AM and SL were dissected from the homogenate and mounted on photodiode force transducers. VP (0.1-3.0 mmol/l) (and to a lesser degree DT) increased Ca2+-activated tension development of the contractile protains in PM and SL and decreased it in AM (+[4-20]%, +4%, -[14-28]%, respectively). Both drugs increased the submaximal Ca2+-activated tension development at the order of PM = SL greater than AM in a dose-dependent manner. The changes of half-maximal pCa50 at 1 mmol/l VP were 0.25, 0.25, and 0.15, respectively. For Ca2+ uptake and release from the SR, VP as well as DT (0.1-3.0 mmol/l) in the uptake phase decreased caffeine-induced tension transients in a dose-dependent fashion. At 0.01-3.0 mmol/l, the drugs directly induced Ca2+ release from the SR or enhanced caffeine-induced tension transients with the exception that in PM, DT attenuated caffeine-induced tension transients. Thus, VP and DT have similar intracellular mechanisms of action in striated muscle. Both drugs induced calcium release from the SR and increase Ca2+ sensitivity of the contractile proteins, and thus could be the underlying mechanisms for potentiating twitch tension, and inducing contracture in skeletal muscle.

Mechanisms of ryanodine-induced depression of caffeine-induced tension transients in skinned striated rabbit muscle fibers

Evidence suggests that ryanodine affects ligand-gated calcium channels in the sarcoplasmic reticulum (SR) resulting in depressed muscle contraction. In skinned fibers from striated muscle the effects of ryanodine were examined (1) on Ca2+ uptake and on Ca2+ release to differentiate whether the effects are on the pump or channel, and (2) during the tension transient, with ryanodine exposure at various times either simultaneous with or directly after exposure to caffeine. Of total calcium content in the SR, 25 mM caffeine released greater than 90% in papillary muscle (PM), approximately equal to 25% in soleus (SL), and approximately equal to 20% in adductor magnus (AM). Ryanodine (100 microM for 1-3 s for AM and SL; 1 microM for 7-10 s for PM), in the initial loading phase, did not significantly change, and in the initial release phase, markedly depressed the subsequent control caffeine-induced tension transients (C2) in all three muscle types. The depression increased with increasing time of exposure to ryanodine (10 microM) in the order of PM greater than AM greater than SL. Upon introduction of ryanodine after caffeine-induced tension transients, maximal depression was observed at half-maximum rise of the tension transient, followed by recovery of depression to completion in SL, and only partially in AM and PM at steady state of relaxation. The extent of recovery was in the order of SL greater than AM greater than PM. The data suggest that ryanodine affects Ca2+ releasing channel as a result of its binding to open channels.

Effects of ryanodine on skinned myocardial fibers of the rabbit

Skinned fiber bundles from papillary muscle of rabbits were used to study the effects of ryanodine (1) on direct Ca2+ activation of the contractile proteins, and (2) on direct Ca2+ uptake and release from the sarcoplasmic reticulum (SR). Caffeine (25 mM) was used to release Ca2+ from the SR and to generate a tension transient. Each tension transient occurred after sequential immersion of the fiber bundles into five solutions: loading (uptake phase, [U]) and releasing (release phase, [R]). The height of free Ca2+-activated tension development of the contractile proteins, and the area of the tension transient generated by caffeine were assessed. (1) The direct free Ca2+-activated tension development of the contractile proteins was not significantly affected by ryanodine up to 0.1 mM, either at the submaximal or maximal free Ca2+ concentrations. (2) Ryanodine (1 nM-1 microM), in U, R, or in U and R, did not significantly change the immediate caffeine-induced tension transients. In the same preparation after ryanodine treatments, the second control caffeine-induced tension transients (C2, no ryanodine) were decreased in a dose-dependent manner (IC50 = 50 nM, 10 nM, 10 nM for R, U, and U and R, respectively). The depression caused by ryanodine on the SR was "activity"-dependent and not readily reversible. Total calcium content in the SR of C2 was not significantly changed by small quantities of ryanodine (less than 0.1 microM) and was decreased with greater amounts of ryanodine (greater than or equal to 0.1 microM). Thus, at low concentrations of ryanodine, the negative inotropic action is due to decrease Ca2+ release from the SR; at high concentration of ryanodine, it is due to decrease in calcium accumulation in the SR.

Comparison of the effects of halothane on newborn and adult rabbit myocardium

The effect of halothane on myocardial contractility was studied in isolated right ventricular muscle preparations from newborn and adult rabbits. Right ventricular strips were mounted in oxygenated Krebs' solution and stimulated with supramaximal voltages at 1.0 Hz, while isometric force of contraction was continuously recorded. Halothane (0.4, 0.7, and 1.1%) caused a significant dose-dependent depression of both peak developed tension (42, 61, and 70%, respectively) and maximum rate of rise of isometric tension (40, 56, and 64%, respectively) of newborn myocardium. Newborn myocardial preparations exhibited approximately 20% greater depression of contractility than adult myocardium at each concentration studied (P less than 0.05), thus a parallel shift of the dose-response curves was observed. It was concluded that halothane exerts a potent depressant effect on newborn myocardium that is greater than that on adult myocardium. The depression effect of halothane on the newborn myocardium may contribute to its hypotensive effect in newborn infants.

Effects of ryanodine on skinned skeletal muscle fibers of the rabbit

The mechanism(s) of ryanodine-induced contracture of skeletal muscle were studied in skinned fibers from soleus (SL) and adductor magnus (AM) (slow- and fast-twitch skeletal muscles) of rabbits. Pieces of SL or AM were homogenized (sarcolemma disrupted). Single fibers were dissected from the homogenate and mounted on photodiode force transducers. At concentrations 1-50 microM, ryanodine slightly but significantly increased the submaximal Ca2+-activated tension development of the contractile proteins in skinned fibers of AM but not of SL. Ryanodine in uptake phase or release phase increased caffeine-induced tension transients in the SR of both muscle types; however, no dose-response relation was found. Ryanodine greater than or equal to 1 microM decreased, however, the second control tension transients in a dose-dependent manner. The depression was nearly irreversible and "activity"-dependent. The concentrations of ryanodine that inhibited the second control tension transients by 50% were 10 microM and 5 microM for SL and AM, respectively, following ryanodine administration in the release phase, and 100 microM and 30 microM, respectively, for these preparations after the drug was present in the uptake phase. The quantity of calcium released from the SR by Triton X-100 and caffeine in the second control tension transient was unchanged by ryanodine at all concentrations tested when compared with that of the absence of ryanodine. The present findings suggest that the ability of ryanodine to increase immediate calcium release from the SR, and in AM but not SL, to increase the sensitivity of the contractile proteins to Ca2+ underlies the contracture caused by this agent in intact skeletal muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

24xi-Methyl 5 alpha-cholestane-3 alpha,6 beta,9 alpha,25-tetrol 24-monoacetate, a novel polyhydroxylated steroid from the soft coral Sarcophyton tortuosum

A novel polyhydroxylated steroid, named sartortuosterol A, with rare 3 alpha- and 6-hydroxyl groups, was isolated from the South China Sea soft coral Sarcophyton tortuosum Tixier-Durivault, and its structure was established as 24xi-methyl 5 alpha-cholestane-3 alpha, 6 beta, 9 alpha,25-tetrol 25-monoacetate from spectroscopic data and chemical conversions.

Intracellular mechanism of action of isoflurane and halothane on striated muscle of the rabbit

Studies were conducted on the effects of isoflurane and halothane on intracellular mechanisms of striated muscle contraction: Ca2+ activation of the contractile proteins and Ca2+ uptake and release from the sarcoplasmic reticulum. Functionally skinned muscle fibers (sarcolemma disrupted by homogenization) from isolated papillary muscle (PM), soleus (SL) (slow-twitch skeletal muscle), and adductor magnus (AM) (fast-twitch skeletal muscle) of rabbits were mounted on a photodiode tension transducer. They were immersed in control solution (saturated with N2), then in test solution (saturated with anesthetic-N2 mixture), and in control solution again. The following two studies were carried out: 1) in the study of Ca2+ -activated tension development of the contractile proteins, free Ca2+ concentration in the bathing solution was controlled by the use of a high EGTA (7 mM), and 2) in the study of Ca2+ uptake and release from the sarcoplasmic reticulum (SR), Ca2+ was loaded into the SR and released with caffeine and the resulting tension transients were measured. Isoflurane (1-4%) decreased (6-9%) the maximal Ca2+ -activated tension development in PM and SL but more in PM than in SL. In AM, however, isoflurane and halothane (1-3%) produced no change. Isoflurane decreased submaximal Ca2+ -activated tension development in PM, but effected no change in it in SL. Isoflurane and halothane increased the tension development in AM to the extent of producing a shift to the left in the pCa-tension curves of less than or equal to 0.1 pCa unit.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of halothane and verapamil in isolated papillary muscle

The combined depressant effects of verapamil and halothane on myocardial contractility were studied using isolated papillary muscle from the rabbit. Verapamil alone (0.5 microM) significantly decreased peak developed tension (PDT) by 15 +/- 2%, time to peak tension (TPT) by 10 +/- 1%, and maximum rate of increase of tension (+dT/dt) by 5 +/- 1%, but not maximum rate of decrease of tension (-dT/dt). Halothane alone (0.8%) significantly decreased PDT by 56 +/- 2%, TPT by 11 +/- 2%, +dT/dt by 53 +/- 2%, and -dT/dt by 56 +/- 2%. During the exposure period, the combination of verapamil and halothane together produced a simple additive effect (no significant interaction effect by two-way analysis of variance), with PDT decreased by 68 +/- 2%, TPT by 20 +/- 3%, +dT/dt by 62 +/- 2%, and -dT/dt by 65 +/- 2%. The reversibility of halothane-induced depression was also studied. Peak developed tension showed complete reversibility 30 min after discontinuing halothane. In the presence of verapamil, however, the reversibility of halothane-induced depression was not complete, and significant residual depression of PDT (19 +/- 3%) was observed. We conclude that the acute depressant effect of verapamil plus halothane in isolated papillary muscle is additive, but reversibility of halothane-induced depression may be impaired or prolonged in the presence of verapamil.

Effects of (+)-propranolol on intracellular mechanisms of contraction in striated muscle of the rabbit

In functionally skinned muscle fibers from the rabbit, we studied the effect of propranolol on calcium activation of the contractile proteins and, in separate experiments, on calcium uptake and release from the sarcoplasmic reticulum (SR) while measuring physiological tension. Pieces from isolated papillary muscle (PM), soleus (SL) (slow-twitch skeletal muscle), and adductor magnus (AM) (fast-twitch skeletal muscle) were homogenized (sarcolemma disrupted). A fiber bundle from PM and single fibers from SL and AM were dissected from the homogenate and mounted on a photodiode tension transducer. To study Ca2+-activated tension development of the contractile proteins, we used high EGTA (7 mmol/l) to control the free calcium concentration. To study SR function, we used five different solutions to load the calcium into the SR and to release it from the SR with 25 mmol/l caffeine, thus producing a tension transient. In general, propranolol has similar mechanisms of action in the three muscle types. Propranolol (0.1-1.0 mmol/l) increased the submaximal calcium-activated tension development in all muscles but with PM = SL greater than AM, and this increase was correlated with increases in calcium binding to isolated troponin C. Propranolol increased the maximal calcium-activated tension development in PM and SL, but decreased that in AM. Propranolol at concentrations of 0.3-1.0 mmol/l decreased calcium uptake by the SR but did not change calcium release in any of the three muscles. In PM, however, propranolol at a concentration of 0.1 mmol/l increased calcium uptake by the SR. We conclude that propranolol induces decreases in muscle contraction mainly by decreasing calcium uptake by the SR.

Differences in threshold for protamine toxicity in isolated atrial and ventricular tissue

The inotropic and chronotropic effects of protamine sulfate on rabbit myocardium were studied using isolated preparations of atrial and ventricular tissue. Each tissue differed markedly in its susceptibility to depression of peak isometric developed tension. The threshold concentration for depression of tension was 0.022% for left atrium, 0.055% for right atrium, and 0.3% for right ventricular papillary muscle. Tension in the left atrial preparation increased 20% over control at a protamine concentration of 0.02%, but decreased to less than 30% of control at a concentration of 0.022%. Right atrial tissue tension decreased to 48% of control at a protamine concentration of 0.055% and then to 17% of control at a concentration of 0.6%. In papillary muscle, tension decreased to 64% of control at a concentration of 0.3% and then to 9% of control at a concentration of 0.35%. Thus a very steep dose-response curve was observed for each tissue. In the right atrium-sinoatrial node preparation, administration of protamine at concentrations of 0.05-0.06% produced intermittent atrial extrasystoles, but no significant change in overall rate of discharge. The narrow margin of safety of the protamine dose-response curve may provide a partial explanation for the precipitous nature of hypotensive episodes during clinical administration.