scholarly journals Graded Activation in Frog Muscle Fibers

1973 ◽  
Vol 61 (4) ◽  
pp. 424-443 ◽  
Author(s):  
L. L. Costantin ◽  
S. R. Taylor
Keyword(s):  
Membrane Potential ◽  
Voltage Clamp ◽  
Cross Section ◽  
Muscle Fibers ◽  
Frog Muscle ◽  
Single Muscle ◽  
Fiber Cross Section ◽  
Striation Spacing ◽  
Velocity Of Shortening ◽  
Electrode Voltage

The membrane potential of frog single muscle fibers in solutions containing tetrodotoxin was controlled with a two-electrode voltage clamp. Local contractions elicited by 100-ms square steps of depolarization were observed microscopically and recorded on cinefilm. The absence of myofibrillar folding with shortening to striation spacings below 1.95 µm served as a criterion for activation of the entire fiber cross section. With depolarizing steps of increasing magnitude, shortening occurred first in the most superficial myofibrils and spread inward to involve axial myofibrils as the depolarization was increased. In contractions in which the entire fiber cross section shortened actively, both the extent of shortening and the velocity of shortening at a given striation spacing could be graded by varying the magnitude of the depolarization step. The results provide evidence that the degree of activation of individual myofibrils can be graded with membrane depolarization.

scholarly journals Extracellular Hco3− Dependence of Electrogenic Na/Hco3 Cotransporters Cloned from Salamander and Rat Kidney

2000 ◽  
Vol 115 (5) ◽  
pp. 533-546 ◽  
Author(s):  
Irina I. Grichtchenko ◽  
Michael F. Romero ◽  
Walter F. Boron
Keyword(s):  
Membrane Potential ◽  
Voltage Clamp ◽  
Xenopus Oocytes ◽  
Rat Kidney ◽  
Outward Current ◽  
Membrane Vesicles ◽  
Disulfonic Acid ◽  
Ambystoma Tigrinum ◽  
Ph Titration ◽  
Electrode Voltage

We studied the extracellular [HCOabstract 3 −] dependence of two renal clones of the electrogenic Na/HCO3 cotransporter (NBC) heterologously expressed in Xenopus oocytes. We used microelectrodes to measure the change in membrane potential (ΔVm) elicited by the NBC cloned from the kidney of the salamander Ambystoma tigrinum (akNBC) and by the NBC cloned from the kidney of rat (rkNBC). We used a two-electrode voltage clamp to measure the change in current (ΔI) elicited by rkNBC. Briefly exposing an NBC-expressing oocyte to HCOabstract 3 −/CO2 (0.33–99 mM HCOabstract 3−, pHo 7.5) elicited an immediate, DIDS (4,4-diisothiocyanatostilbene-2,2-disulfonic acid)-sensitive and Na+-dependent hyperpolarization (or outward current). In ΔVm experiments, the apparent Km for HCOabstract 3− of akNBC (10.6 mM) and rkNBC (10.8 mM) were similar. However, under voltage-clamp conditions, the apparent Km for HCOabstract 3− of rkNBC was less (6.5 mM). Because it has been reported that SOabstract 3=/HSO abstract 3− stimulates Na/HCO3 cotransport in renal membrane vesicles (a result that supports the existence of a COabstract 3= binding site with which SOabstract 3= interacts), we examined the effect of SOabstract 3=/HSO abstract 3− on rkNBC. In voltage-clamp studies, we found that neither 33 mM SOabstract 4= nor 33 mM SOabstract 3 =/HSOabstract 3− substantially affects the apparent Km for HCO abstract 3−. We also used microelectrodes to monitor intracellular pH (pHi) while exposing rkNBC-expressing oocytes to 3.3 mM HCOabstract 3 −/0.5% CO2. We found that SO abstract 3=/HSOabstract 3 − did not significantly affect the DIDS-sensitive component of the pHi recovery from the initial CO2 -induced acidification. We also monitored the rkNBC current while simultaneously varying [CO2]o, pHo, and [COabstract 3=]o at a fixed [HCOabstract 3−]o of 33 mM. A Michaelis-Menten equation poorly fitted the data expressed as current versus [COabstract 3=]o . However, a pH titration curve nicely fitted the data expressed as current versus pHo. Thus, rkNBC expressed in Xenopus oocytes does not appear to interact with SOabstract 3 =, HSOabstract 3−, or COabstract 3=.

scholarly journals Membrane Dysfunction Induced by In Vitro Ischemia in Rat Hippocampal CA1 Pyramidal Neurons

1999 ◽  
Vol 81 (4) ◽  
pp. 1872-1880 ◽  
Author(s):  
E. Tanaka ◽  
S. Yamamoto ◽  
H. Inokuchi ◽  
T. Isagai ◽  
H. Higashi
Keyword(s):  
Membrane Potential ◽  
Voltage Clamp ◽  
Pyramidal Neurons ◽  
Membrane Surface ◽  
Bathing Medium ◽  
Ca1 Pyramidal Neurons ◽  
In Vitro Ischemia ◽  
Hippocampal Ca1 ◽  
Electrode Voltage

Membrane dysfunction induced by in vitro ischemia in rat hippocampal CA1 pyramidal neurons. Intracellular and single-electrode voltage-clamp recordings were made to investigate the process of membrane dysfunction induced by superfusion with oxygen and glucose-deprived (ischemia-simulating) medium in hippocampal CA1 pyramidal neurons of rat tissue slices. To assess correlation between potential change and membrane dysfunction, the recorded neurons were stained intracellularly with biocytin. A rapid depolarization was produced ∼6 min after starting superfusion with ischemia-simulating medium. When oxygen and glucose were reintroduced to the bathing medium immediately after generating the rapid depolarization, the membrane did not repolarize but depolarized further, the potential reaching 0 mV ∼5 min after the reintroduction. In single-electrode voltage-clamp recording, a corresponding rapid inward current was observed when the membrane potential was held at −70 mV. After the reintroduction of oxygen and glucose, the current induced by ischemia-simulating medium partially returned to preexposure levels. These results suggest that the membrane depolarization is involved with the membrane dysfunction. The morphological aspects of biocytin-stained neurons during ischemic exposure were not significantly different from control neurons before the rapid depolarization. On the other hand, small blebs were observed on the surface of the neuron within 0.5 min of generating the rapid depolarization, and blebs increased in size after 1 min. After 3 min, neurons became larger and swollen. The long and transverse axes and area of the cross-sectional cell body were increased significantly 1 and 3 min after the rapid depolarization. When Ca2+-free (0 mM) with Co2+ (2.5 mM)-containing medium including oxygen and glucose was applied within 1 min after the rapid depolarization, the membrane potential was restored completely to the preexposure level in the majority of neurons. In these neurons, the long axis was lengthened without any blebs being apparent on the membrane surface. These results suggest that the membrane dysfunction induced by in vitro ischemia may be due to a Ca2+-dependent process that commences ∼1.5 min after and is completed 3 min after the onset of the rapid depolarization. Because small blebs occurred immediately after the rapid depolarization and large blebs appeared 1.5–3 min after, it is likely that the transformation from small to large blebs may result in the observed irreversible membrane dysfunction.

scholarly journals The Effect of Bathing Solution Tonicity on Resting Tension in Frog Muscle Fibers

1973 ◽  
Vol 62 (6) ◽  
pp. 737-755 ◽  
Author(s):  
J. Lännergren ◽  
J. Noth
Keyword(s):  
Cross Section ◽  
Short Range ◽  
Muscle Fibers ◽  
Bathing Solution ◽  
Direct Function ◽  
Fiber Cross Section ◽  
Resting Tension ◽  
Hypertonic Solutions ◽  
Cross Section Area ◽  
Section Area

Resting tension and short-range elastic properties of isolated twitch muscle fibers of the frog have been studied while bathed by solutions of different tonicities. Resting tension in isotonic solution at 2.3-µm sarcomere spacing averaged 0.46 mN·mm-2 and was proportional to the fiber cross-section area. Hypertonic solutions, containing 0.1–0.5 mM tetracaine to block contracture tension, caused a small sustained tension increase, which was proportional to the fiber cross-section area and which reached 0.9 mN·mm-2 at two times normal tonicity (2T). Further increases in tonicity caused little increase in tension. Hypotonic solutions decreased tension. Thus, tension at 2.3 µm is a continuous, direct function of tonicity. The dependence of tension on tonicity lessened at greater sarcomere lengths. At 3.2 µm either a very small rise or, in some fibers, a fall in tension resulted from an increase in tonicity. Hypertonic solutions also decreased the tension of extended sarcolemma preparations. In constant-speed stretch experiments the elastic modulus, calculated from the initial part of the stretch response, rose steeply with tonicity over the whole range investigated (1–2.5T). The results show that tension and stiffness of the short-range elastic component do not increase in parallel in hypertonic solutions.

scholarly journals The Suppression of the Late After-Potential in Rubidium-Containing Frog Muscle Fibers

1965 ◽  
Vol 48 (6) ◽  
pp. 1003-1010 ◽  
Author(s):  
D. C. Hellam ◽  
D. A. Goldstein ◽  
L. D. Peachey ◽  
W. H. Freygang
Keyword(s):  
Membrane Potential ◽  
Potassium Concentration ◽  
Muscle Fibers ◽  
Frog Muscle ◽  
Muscle Membrane ◽  
Potassium Permeability ◽  
Intracellular Potassium ◽  
Intracellular Potassium Concentration

The late after-potential that follows trains of impulses in frog muscle fibers is virtually absent when most of the intracellular potassium is replaced by rubidium and the muscle is immersed in rubidium-containing Ringer's fluid. Its amplitude is also reduced in freshly dissected, potassium-containing muscle fibers that are immersed directly in Rb-Ringer's fluid. These findings are discussed in terms of the model for muscle membrane of Adrian and Freygang (1962 a, b) and in relation to the report of Adrian (1964) that Rb-containing muscle fibers do not exhibit the variations in potassium permeability as a function of membrane potential that are found in fibers with normal intracellular potassium concentration immersed in Ringer's fluid.

Single-electrode voltage-clamp analysis of the N-methyl-D-aspartate component of synaptic responses in neocortical slices from children with intractable epilepsy

1992 ◽  
Vol 67 (1) ◽  
pp. 84-93 ◽  
Author(s):  
J. P. Wuarin ◽  
W. J. Peacock ◽  
F. E. Dudek
Keyword(s):  
Electrical Stimulation ◽  
Membrane Potential ◽  
Nmda Receptor ◽  
Voltage Clamp ◽  
Intractable Epilepsy ◽  
Perfusion Solution ◽  
Electrode Voltage ◽  
Voltage Dependent ◽  
Abnormal Tissue ◽  
Synaptic Responses

1. Synaptic transmission mediated by the N-methyl-D-aspartate (NMDA)-receptor type was studied in neocortex from children undergoing surgical treatment for intractable epilepsy. Intracellular recordings from pyramidal cells were obtained in slices of neocortical tissue by use of microelectrodes. Synaptic responses were induced by electrical stimulation and studied with current-clamp and single-electrode voltage-clamp techniques. The NMDA-receptor-mediated component of the synaptic responses was isolated by addition of 10 microM bicuculline and 30 microM 6-cyano-2,3-dihydroxy-7-nitroquinoxaline (CNQX) in the perfusion solution. 2. In the presence of bicuculline and CNQX, electrical stimulation evoked an excitatory postsynaptic potential (EPSP) in every recorded cell. The amplitude of this EPSP increased when membrane potential was depolarized with injected current. 3. All cells studied in voltage clamp were recorded with microelectrodes containing Cs+ and QX 314. To avoid contamination of the responses from voltage-dependent Ca2+ conductances, membrane potential was held at depolarized potentials until Ca2+ spiking inactivated completely. The evoked excitatory postsynaptic currents (EPSCs) measured at resting membrane potential ranged from 100 to 400 pA. The NMDA receptor-selective antagonist DL-2-amino-5-phosphonopentanoic acid (AP-5) reversibly decreased the current amplitude by 60% for 10 microM and 80% for 30 microM. 4. The current-voltage (I-V) relation showed a region of negative slope conductance between -100 and -20 mV. The largest currents (-250 to -900 pA) were recorded in the range of -45 to -20 mV and reversed between -10 and +10 mV. Removing Mg2+ from the perfusion solution decreased the negativity of the slope, which is consistent with a reduction in the voltage-dependent Mg2+ block of the NMDA-receptor channel. 5. The I-V plots obtained from cells recorded in the most abnormal tissue were averaged and compared with those from the least abnormal tissue. No significant difference was found between these two groups. The averaged plots from the youngest patients (8 and 10 mo old) and those from the oldest (5-15 yr old) patients were also compared, and the results from these two groups were not significantly different.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Voltage Clamp Experiments on Single Muscle Fibers of Rana pipiens

1972 ◽  
Vol 60 (1) ◽  
pp. 1-19 ◽  
Author(s):  
L. E. Moore
Keyword(s):  
Voltage Clamp ◽  
Rana Pipiens ◽  
Muscle Fibers ◽  
Petroleum Jelly ◽  
Single Muscle ◽  
Transverse Tubular System ◽  
Anomalous Rectification ◽  
Outward Currents ◽  
Delayed Rectification ◽  
Tubular System

A voltage clamp for single muscle fibers has been developed. Stability of the system was achieved when an artificial node was created by enclosing a single muscle fiber in a petroleum jelly seal which served as an analogue of the myelin sheath. Typical voltage clamp records were obtained with large inward transient currents followed by a delayed rectification of the outward currents. These currents looked qualitatively similar when the transverse tubular system was destroyed. Errors in current measurement, especially those due to anomalous rectification, are discussed.

scholarly journals The Influence of Sodium-Free Solutions on the Membrane Potential of Frog Muscle Fibers

1963 ◽  
Vol 47 (1) ◽  
pp. 117-132 ◽  
Author(s):  
L. J. Mullins ◽  
K. Noda
Keyword(s):  
Membrane Potential ◽  
Activity Coefficients ◽  
Muscle Fibers ◽  
Frog Muscle ◽  
Sartorius Muscle ◽  
Coupling Ratio ◽  
Nernst Equation ◽  
Ringer’S Solution ◽  
Na Efflux ◽  
Frog Sartorius

The membrane potential of frog sartorius muscle fibers in a Cl- and Na-free Ringer's solution when sucrose replaces NaCl is about the same as that in normal Ringer's solution. The K+ efflux is also about the same in the two solutions but muscles lose K and PO4 in sucrose Ringer's solutions. The membrane potential in sucrose Ringer's solution is equal to that given by the Nernst equation for a K+ electrode, when corrections are made for the activity coefficients for K+ inside and outside the fiber. For a muscle in normal Ringer's solution, the measured membrane potential is within a few millivolts of EK. This finding is incompatible with a 1:1 coupled Na-K pump. It is consistent with either no coupling of Na efflux to K influx, or a coupling ratio of 3 or greater.

Kinetics of L-glutamate influx in single barnacle muscle fibers under 0-trans conditions

1992 ◽  
Vol 262 (6) ◽  
pp. C1485-C1490
Author(s):  
L. W. Horn
Keyword(s):  
Membrane Potential ◽  
Cell Membrane ◽  
Binding Site ◽  
Kinetic Models ◽  
Glutamate Uptake ◽  
Muscle Fibers ◽  
Single Muscle ◽  
Constant Flux ◽  
Kinetics Of ◽  
Barnacle Muscle Fibers

The dependence of L-glutamate influx on extracellular Na and L-glutamate concentrations was determined using internally dialyzed single muscle fibers of Balanus nubilus. Internal Na and glutamate concentrations were held at zero, and the cell membrane potential was constant. Flux activation curves for external glutamate were measured for five different external Na concentrations, and flux activation curves for external Na were measured independently for three different external glutamate concentrations. An analysis of alternative kinetic models for the transporter mechanism was made and led to the conclusions that under 0-trans conditions the Na:glutamate stoichiometry is 1:1, that glutamate first binding to the external transporter binding site is the preferred order under most extracellular conditions, and that the Na:glutamate coupling is too tight to permit measurable Na-independent glutamate uptake by the transporter.

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