Biomedical subjects

G Suarez-Kurtz

Publications and source records attributed to G Suarez-Kurtz.

At least 55 records · Page 3Linked to original sources

PubMed1989

Effects of aminoglycoside antibiotics on calcium action potentials and calcium channel currents.

The author reviews work from his laboratory on the effects of neomycin and streptomycin on the Ca(2+)-dependent electrogenesis of crustacean muscle fibers and on two distinct Ca2+ channel currents of pituitary cells. The data indicate that these aminoglycosides inhibit the graded electrogenesis and the action potentials of crustacean muscle; these effects are accompanied by inhibition of tension development upon membrane depolarization. Increasing the extracellular Ca2+ concentration reverses the aminoglycoside-induced blockade of the Ca(2+)-dependent electrogenesis of the muscle fibers. Neomycin blocked both the transient (T-type) and the slowly-inactivating (L-type) Ca2+ currents of clonal pituitary GH3 cells, studied with the whole cell modality of the patch clamp technique. The blockade of these currents was not modulated by activation or inactivation of the channels. Neomycin inhibited also the currents conveyed by Na+ through the slowly-inactivating Ca2+ in cells equilibrated with Ca(2+)-free media. Interpretation of these data led to the suggestion that the blockade of Ca2+ currents by neomycin (and other aminoglycosides) cannot be explained by competition with Ca2+ ions for binding to high affinity transition sites within the Ca2+ channel path.

Action Potentials↗

PubMed1988

Release of sarcoplasmic enzymes from skeletal muscle by Bothrops jararacussu venom: antagonism by heparin and by the serum of South American marsupials.

The venom of B. jararacussu induced a time- and dose-dependent (2-100 micrograms/ml) increase in the rate of release of sarcoplasmic enzymes (CK and LDH) from isolated rat and frog muscles. This effect, which we attribute to sarcolemmal damage by the venom, persisted in a Ca2+-free media, suggesting that phospholipase A activity was not required. The venom-induced enzyme release from the isolated muscles was reversibly inhibited by the sera (1-10 microliters/ml) of the marsupials Didelphis marsupialis aurita and Philander opossum, by an acidic glycoprotein fraction isolated from the opossum serum (50 micrograms/ml), and by heparin (50 micrograms/ml). Incubation of the B. jararacussu venom with opossum sera or heparin prevented the increase in plasma CK level observed in mice in which the snake venom (2.5-5.0 micrograms/g) was injected i.m. It is suggested that formation of acid-base complexes between basic myotoxins of B. jararacussu venom and either acidic components in the marsupial sera or the polyanionic heparin could account for the inhibition of the in vitro and in vivo effects of the venom on the release of sarcoplasmic enzymes from skeletal muscles.

Animals↗

PubMed1988

Effects of dichlorobenzamil on calcium currents in clonal GH3 pituitary cells.

Membrane currents were recorded from voltage-clamped clonal (GH3) pituitary cells, using the whole-cell patch clamp method. Under conditions in which currents through Na+ and K+ channels were abolished, two distinct Ca++ channel currents were identified. Dichlorobenzamil (DCB), an amiloride analog and potent inhibitor of Na-Ca exchange, inhibited both the T-type Ca++ current (ICa,t) and slowly-inactivating L-type current carried by either Ca++ (ICa,s) or Ba++ (IBa,s). The blockade was dose-dependent (1-25 microM) and ICa,t was more sensitive to inhibition by DCB than the L-type channel currents. Although the inhibition of ICa,t was not accompanied by changes in the time course of inactivation of the T-type channels, the blockade of L-type Ca++ channel currents was time-dependent, increasing throughout the depolarizing test pulse (300 msec). Repetitive stimulation at 1.0 Hz or the application of depolarizing prepulses augmented the blockade of ICa,s and IBa,s by DCB. It is proposed that the blockade is modulated by the functional state of the L-type channel, being enhanced by the channel opening. Currents conveyed by Na+ ions through both types of Ca++ channels in GH3 cells equilibrated with Ca++-free salines were inhibited by DCB concentrations (1-5 microM) comparable to those required for blocking the currents conveyed by Ca++ or Ba++ ions.

Amiloride↗

PubMed1988

Effects of dichlorobenzamil, a sodium-calcium exchange inhibitor, on the calcium paradox and the sodium withdrawal contractures of frog atrial muscle.

1. The effects of dichlorobenzamil (DCB), an amiloride derivative and potent inhibitor of Na-Ca exchange in cardiac sarcolemmal vesicles and isolated cardiac myocytes, were investigated in two paradigms involving Na-Ca exchange, namely the Ca2+ paradox and the Na+-withdrawal contractures of frog atrial muscle strips. 2. Pretreatment with DCB (10-100 microM) inhibited in a dose-dependent manner the contractures elicited by reexposure of the atrial strips to the control Ringer solution after a 5-20 min equilibration with a Ca2+-free saline (Ca2+-readmission contractures; Ca2+ paradox). These contractures were not inhibited, however, when DCB was applied after the preparation had been exposed to the Ca2+-free saline, but before the reexposure to the control Ringer solution. 3. DCB (10-100 microM) did not inhibit the contractures elicited by Na+-deficient saline (Na+-withdrawal contractures) in atrial strips pretreated or not with acetylstrophantydin. This result suggests that, under our experimental conditions, DCB failed to substantially inhibit the Ca2+ influx mediated by Na-Ca exchange. 4. The duration of the plateau of the action potentials of atrial cells equilibrated with Ca2+-free saline was reduced from 1.42 +/- 0.27 s to 0.61 +/- 0.13 s by 50 microM DCB (P less than 0.001). This was attributed to blockade of Na+ currents through modified L-type Ca2+ channels. 5. It is proposed that the shortening of the Na+-dependent action potentials can account for the inhibition of the Ca2+-readmission contractures, because these contractures have a steep dependence on the Na+ influx and intracellular Na+ accumulation that occurs during the Ca2+-free period. 6. The results of this study support the conclusion that DCB has multiple effects on heart muscle, including a potent blockade of Ca2+ channels, and its use as a selective inhibitor of Na-Ca exchange in cellular systems is unwarranted.

Amiloride↗

PubMed1988

Release of creatine kinase from skeletal muscles by Bothrops venoms: heparin potentiation of inhibition by antivenin.

The glycosaminoglycan, heparin (50 micrograms/ml) inhibited the increase in creatine kinase (CK) released from rat extensor digitorum longus (EDL) muscles exposed to Bothrops jararaca venom (150 micrograms/ml). Heparin (2 micrograms/ml) and polyvalent antivenin (0.5 microliter/ml) did not affect the increase in CK release induced by exposure of the muscles to 50 micrograms/ml B. jararacussu venom. Simultaneous exposure of the muscles to venom plus heparin (2 micrograms/ml) plus antivenin (0.5 or 1 microliter/ml) reduced CK release after 160 min by 50% and 80% compared to that induced by venom alone. These changes in CK release from rat EDL muscle show that heparin inhibits the myotoxic effects of Bothrops venoms and increases the potency of their antivenin.

Animals↗

PubMed1987

Currents carried by sodium ions through transient calcium channels in clonal GH3 pituitary cells.

The transient or T-type Ca channel currents of voltage-clamped clonal (GH3) pituitary cells were studied after blockade of Na and K channels. Removal of Ca ions from the bathing medium abolished the Ca currents and allowed Na ions to convey current through the transient channels. These Na currents (I Na,t) were activated at threshold potentials of ca. -85 mV, reached peak amplitudes (up to 2,000 pA) at -60 mV, and were 50% inactivated at holding membrane potentials of -110 to -120 mV. The time constant for inactivation of the maximal I Na,t was 12 +/- 2.4 msec (compared with 22.1 =/- 0.85 msec for maximal I Ca,t). The I Na,t was insensitive to tetrodotoxin (1 micron) and to nimodipine (200 nM) but was abolished by 100 micron external [Ca2+]. It is suggested that high affinity Ca binding sites in the channel modulate the ion selectivity and the current flow through T-type Ca channels.

Action Potentials↗

PubMed1987

Effects of neomycin on calcium channel currents in clonal GH3 pituitary cells.

Membrane Ca currents were recorded from voltage-clamped clonal (GH3) pituitary cells under conditions where currents through Na and K channels were abolished. Two Ca currents, with distinct kinetics and voltage dependence for activation and inactivation, were identified. Neomycin, an aminoglycoside polycation, inhibited both the "transient" (ICa,t) and the "slowly-inactivating" (ICa,s) Ca currents in a dose-dependent manner (100-1,000 microM). The blockade was reversible and ICa,s was more sensitive to neomycin than ICa,t. The inhibition of ICa,s was frequency and time-independent, and was not affected by changes in the holding membrane potential (-35 to -100 mV). Neomycin did not affect the voltage dependence for inactivation of ICa,t. The blockade of both Ca currents by neomycin is ascribed to the general property of aminoglycosides to compete with, and displace Ca ions from membrane binding sites that determine the currents and selectivity of Ca channels. Because comparable concentrations of neomycin were required for blocking the currents conveyed by Ca or, in the absence of external divalent cations, by Na ions through the slowly-inactivating Ca channels, we suggest that the neomycin binding sites are distinct from the high-affinity transition sites within the Ca channel path.

Cells, Cultured↗

PubMed1987

Studies of the halothane-cooling contractures of skeletal muscle.

The characteristics of transient contractures elicited by rapid cooling of frog or mouse muscles perfused in vitro with solutions equilibrated with 0.5-2.0% halothane are reviewed. The data indicate that these halothane-cooling contractures are dose dependent and reproducible, and their amplitude is larger in muscles containing predominantly slow-twitch type fibers, such as the mouse soleus, than in muscles in which fast-twitch fibers predominate, such as the mouse extensor digitorum longus. The halothane-cooling contractures are potentiated in muscles exposed to succinylcholine. The effects of Ca2+-free solutions, of the local anesthetics procaine, procainamide, and lidocaine, and of the muscle relaxant dantrolene on the halothane-cooling contractures are consistent with the proposal that the halothane-cooling contractures result from synergistic effects of halothane and low temperature on Ca sequestration by the sarcoplasmic reticulum. Preliminary results from skinned rabbit muscle fibers support this proposal. The halothane concentrations required for the halothane-cooling contractures of isolated frog or mouse muscles are comparable with those observed in serum of patients during general anesthesia. Accordingly, fascicles dissected from muscle biopsies of patients under halothane anesthesia for programmed surgery develop large contractures when rapidly cooled. The amplitude of these halothane-cooling contractures declined with the time of perfusion of the muscle fascicles in vitro with halothane-free physiological solutions. It is suggested that the halothane-cooling contractures could be used as a simple experimental model for the investigation of the effects of halothane on Ca homeostasis and contractility in skeletal muscle and for study of drugs of potential use in the management of the contractures associated with the halothane-induced malignant hyperthermia syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthetics, Local↗

PubMed1987

Interaction of Bothrops venoms and antivenin on the release of creatine kinase from skeletal muscle.

A polyvalent antivenin (5 microliter/ml) inhibited the increase in creatine kinase (CK) release from rat extensor digitorum longus muscles exposed to the venoms of B. jararacussu (20 micrograms/ml) or B. jararaca (150 micrograms/ml). The increase in plasma CK activity induced by intramuscular injection of B. jararacussu venom (2.5 micrograms/g) into mice was reduced by pretreatment with antivenin and was abolished by preincubation of the venom with the antivenin. Changes in CK release from isolated muscles or in plasma CK activity provide simple, quantitative methods for evaluating the effectiveness of antivenin against the myotoxicity of Bothrops venoms.

Animals↗

PubMed1986

The temperature dependence of halothane-induced contractures of skeletal muscle.

Frog muscles bathed in solutions equilibrated with 0.5%-2.0% halothane develop large contractures when cooled to 2-4 degrees C. These halothane-cooling contractures (HCC) are dose dependent and reproducible; they are potentiated by lidocaine (5 mM), abolished by procaine (5 mM), and partially inhibited by procainamide (5 mM) or sodium salicylate (2 mM). The HCC provides a simple model system for investigating the effects of low halothane concentrations on Ca homeostasis and contractility in skeletal muscle.

Anesthetics, Local↗

PubMed1986

Two calcium currents in a smooth muscle cell line.

Membrane currents in small cells of a smooth muscle cell line (A10) derived from embryonic rat thoracic aorta were monitored by the patch electrode whole-cell voltage clamp technique. Three currents, two divalent cation currents, and a Ca2+-activated K+ current have been observed. The latter is readily abolished pharmacologically, allowing the characterization of the divalent cation currents. With a holding potential of -50 mV, a single divalent current, which inactivates slowly, is elicited on depolarization of the membrane potential to values positive to ca. -10 mV. The second divalent cation current is only observed when the holding potential is negative to -55 mV and the membrane is pulsed to values positive to ca. -35 mV. This current is rapidly inactivating, peaking in approximately 5 ms and decaying with a t1/2 of ca. 15 ms at 0 mV when conveyed by Ba2+. The rapidly inactivating divalent cation current is depressed by substitution of Ba2+ for Ca2+ in the bathing solution and is highly insensitive to organic Ca2+ channel blockers. The slowly inactivating channel has more typical characteristics of Ca2+ channels; it is more permeable to Ba2+ than to Ca2+ and is sensitive to modulation by dihydropyridines. These data demonstrate the presence of two distinctly different Ca2+ channels in A10 cells.

Animals↗

PubMed1986

Halothane-cooling contractures of mammalian muscles.

Mouse soleus and extensor digitorum longus muscles exposed to halothane concentrations (0.3-2.0%) that, at room temperature, have no effect on either resting or twitch tension, develop transient contractures when cooled to 2-10 degrees C. The halothane-cooling contractures (HCC) are reproducible and their amplitudes can be graded by both the halothane concentration and the temperature of cooling. Under identical conditions the HCC is significantly larger in soleus as compared to extensor digitorum longus muscles. The maximal HCC in soleus muscles (1-2% halothane, 2 degrees C) reaches 42% of the tetanic tension recorded at 24 degrees C; in extensor digitorum longus the maximum is 12% of tetanic tension. This difference is ascribed to the predominance of slow-twitch fibers in the soleus muscle. Neither membrane depolarization with high [K]0 solutions nor a short (2 min) exposure to Ca-free media inhibits the HCC. The contractures are depressed, however, when the muscles are preequilibrated for 30 min with Ca-free solutions; under these conditions, the muscle twitches and the caffeine-cooling contractures are also depressed. These effects are ascribed to partial depletion of the Ca content of the sarcoplasmic reticulum. The HCC is abolished by 4 mM procaine, partially inhibited by 4 to 10 mM procainamide and potentiated by 4 mM lidocaine, but it is not significantly affected by dantrolene (40 microM). It is proposed that the HCC results from synergistic interaction of halothane and low temperature inhibiting Ca-sequestration by the sarcoplasmic reticulum of the muscle fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthetics, Local↗

PubMed1985

Basic polyaminoacids and protamine stimulate enzyme release from frog muscles.

Polylysines, polyornithine, and protamine increased the release of creatine kinase (CK) and lactate dehydrogenase (LDH) from frog muscles. With 5 micrograms/ml (50 nM) of a polylysine of molecular weight 100,000, enzyme release reached peak values (ten-fold above control) within 30 minutes; subsequent removal of the polylysine did not reduce significantly the release rates. The effectiveness of the polycations increased with the degree of polymerization. Their effects were prevented by pretreatment of the muscles with polyanions (heparin or polyglutamic acids) and were reversed when heparin was applied within 30 minutes of exposure to polylysine. The initial stimulation of enzyme release by polylysine was attenuated by Ca-free solutions and by low temperature (4 degrees C). It is suggested that, while fiber damage can explain the increased loss of sarcoplasmic enzymes after prolonged treatment of frog muscles with polycations, other mechanisms (perhaps exocytosis) are involved in the stimulation of CK and LDH release during brief exposures to nanomolar concentrations of polylysines or polyornithine.

Animals↗

PubMed1985

Excitation-contraction coupling in crab muscle fibers with swollen T tubules.

Single crab (Callinectes danae) fibers were equilibrated with isotonic, high KCl solutions and were subsequently returned to the control saline. This caused marked swelling of the T tubules. Fibers treated with 100 mM KCl had a 2.5-mV residual depolarization, a 50% decrease in effective membrane resistance (Reff) and a 75% reduction in membrane time constant (tau m). These fibers exhibited large increases in membrane conductance upon depolarization and were inexcitable; membrane depolarization with current pulses elicited no contraction. The effects of the KCl treatment on membrane properties were not reproduced by treatment with high potassium gluconate solutions, which did not cause tubular swelling. Tetrabutylammonium (10 mM) or Ba ions (10-20 mM), but not tetraethylammonium (40-100 mM), Sr ions (15-70 mM), or procaine (1-8 mM) reversed the effects of the KCl treatment on Reff, tau m, membrane excitability, and excitation-contraction coupling. The time course of the Ba effects was consistent with the suggestion that the KCl treatment increases the K conductance of the tubular membranes, which in turn prevents the activation of voltage-dependent Ca channels located in the membranes of the T system. This results in inhibition of the Ca-dependent electrogenesis and consequently, the absence of contraction upon depolarization of the plasma membrane.

Animals↗

PubMed1984

Inhibitory effects of salicylate on contractility in skeletal muscle.

Salicylate (1-5 mM) had no effect on the peak amplitude (Pt) of twitches elicited at 0.05 to 0.05 Hz, but depressed the Pt in frog and toad "toe" muscles stimulated at 5 to 10 Hz. The maximal tetanic tension (Po) was not reduced significantly by salicylate, but the time to reach Po was increased to several seconds. K-induced contractures were reduced by ca 40 and 50%, respectively, in the presence of 5 and 10 mM salicylate. Pretreatment with salicylate (5 mM) reduced the twitch potentiation by quinine, shortened the duration of twitches in caffeine-treated muscles and inhibited the caffeine- and the quinine-induced contractures. Muscles in contracture because of a previous exposure to quinine relaxed promptly upon addition of salicylate to the bathing medium. The inhibitory effects of salicylate on Pt, on Po and on K- or drug-induced contractures were reversible and were not affected by changes in pH between 7.5 and 6.5. Salicylate depressed the caffeine-rapid cooling contractures (RCC). In toad muscles, this effect was affected markedly by the order in which caffeine and salicylate were applied. Blockade of the caffeine-RCC by salicylate was enhanced by lowering the pH of the medium. Salicylamide (1-5 mM) reproduced the effects of salicylate on the caffeine- and the quinine-induced contractures and the caffeine-RCC. In addition, salicylamide reduced the twitch tension. It is proposed that salicylate and salicylamide affect Casequestration by the sarcoplasmic reticulum.

Animals↗

PubMed1984

Potassium-induced contractures in crab (Callinectes danae) muscle fibers.

The contractures induced by 20-200 mM [K+]o in single crab muscle fibers were resolved into two components. The first component, consisting of single twitches or brief tetanic contractions, was associated with electrogenic membrane responses. The second occurred after spiking subsided with an amplitude that increased linearly with the [K+]o between 20 and 90 mM. The amplitude and time course of the contractures elicited by a given [K+]o differed markedly between different fibers. Contracture reproducibility of a single fiber was best when 90 mM [K+]o was used. The K-induced contractures were abolished after brief (3 min) exposure of the fibers to a calcium-free solution and were greatly depressed by 8 mM procaine. The data suggest that the contractures require both Ca2+-influx across the sarcolemma and release of Ca2+ stored in the sarcoplasmic reticulum.

Animals↗

PubMed1983

Excitation-contraction coupling: role of K-activation within the transverse tubular system.

Long-duration Ca action potentials induced in crustacean muscle fibers after prolonged exposure to quaternary ammonium ions are accompanied by attenuated tensions with unique time courses. The tensions have three phases. The initial phase, correlated with the upstroke of the spike, is a rapid increase in tension followed by relaxation to or near to resting level (on-tension). In the second phase, tension rises slowly as the spike plateau declines. The final phase is another rapid increase and decay in tension that is correlated with termination of the action potential (off-tension). To observe these tensions, fibers must be exposed to 50-100 mM tetrabutylammonium ion for about 1 hr or to lower concentrations for longer periods (e.g., 5 mM for 20-30 hr). To obtain a similar response in fibers treated with tetraethylammonium ion, higher concentrations or longer soaking periods, or both, are required. Because neither caffeine-induced tensions in intact fibers nor contractile protein and sarcoplasmic reticulum function in skinned fibers were modified by quaternary ammonium ions, their site of action appears to be limited to surface or transverse tubular system membranes, or both. The unique tensions can be explained by considering the mode by which quaternary ammonium ions block K channels in conjunction with a scheme in which activation of K channels within the transverse tubular system controls the driving force for influx of Ca ions.

Action Potentials↗

PubMed1983

Contractions induced by sodium withdrawal in crab (Callinectes danae) muscle fibres.

A study was made of the effects of Na removal on the resting tension of single muscle fibres of the crab Callinectes danae. Reduction of [Na]o (replacement with Li, Tris or choline) below a threshold value, typical for each fibre, induced spontaneous, local contractions randomly dispersed along the fibres; this was followed by propagated contractile waves and tension oscillations. Sustained contractures were occasionally seen at threshold [Na]o and were consistently observed when [Na]o was further reduced. The Na withdrawal contractions depended on [Ca]o and were abolished in Ca-free media; they were restored within seconds after the addition of Ca (3-12 mM) or Sr (15-25 mM), but not Ba (10-100 mM), to the media. Caffeine (0.2-1.0 mM) facilitated, whereas La (2-5 mM), procaine (1 mM) or lidocaine (10 mM) inhibited the Na-withdrawal contractions. It is concluded that increased Ca influx across the sarcolemma and release of stored Ca from the sarcoplasmic reticulum are involved in the contractions induced by Na-deficient solutions in crab fibres.

Anesthetics, Local↗