Phasic efflux of potassium from frog ventricle

1962 ◽  
Vol 203 (2) ◽  
pp. 253-257 ◽  
Author(s):  
Victor Lorber ◽  
John L. Walker ◽  
Ernest A. Greene ◽  
Margaret H. Minarik ◽  
Moon Jae Pak
Keyword(s):  
Cell Membrane ◽  
Action Potential ◽  
Cardiac Cycle ◽  
Pronounced Effect ◽  
Voltage Gradient ◽  
Perfusion Medium ◽  
Actual Increase ◽  
Frog Ventricle ◽  
Turtle Heart ◽  
Do So

A phasic effiux of K42 during the cardiac cycle, first described by Wilde in the turtle heart, has been observed in perfused strips of frog ventricle. This was shown to represent an actual increase in the outward movement of K, occurring during the action potential, and of approximately the same duration as the electrical transient. Perfusion with K-free Ringer's prolonged both events, and, within the limits of resolution of the method, appeared to do so to about the same extent. The level of K in the perfusion medium was found to have a pronounced effect on the K efflux, a result which may be interpreted in terms of an effect of extracellular [K+] on the permeability of the cell membrane to K. The finding that the increase in K efflux observed during the action potential is much smaller than that predicted from the increase in the voltage gradient (assuming the voltage gradient to be the only variable) is consistent with a diminished K conductance during the action potential.

Regression of LV hypertrophy with captopril normalizes membrane currents in rabbits

1998 ◽  
Vol 275 (4) ◽  
pp. H1216-H1224 ◽  
Author(s):  
Seth J. Rials ◽  
Xiaoping Xu ◽  
Ying Wu ◽  
Roger A. Marinchak ◽  
Peter R. Kowey
Keyword(s):  
Cell Membrane ◽  
Action Potential ◽  
Renal Artery ◽  
Current Density ◽  
Action Potential Duration ◽  
Left Ventricular ◽  
Membrane Current ◽  
Membrane Capacitance ◽  
Membrane Currents ◽  
Cell Membrane Capacitance

Recent studies indicate that regression of left ventricular hypertrophy (LVH) normalizes the in situ electrophysiological abnormalities of the left ventricle. This study was designed to determine whether regression of LVH also normalizes the abnormalities of individual membrane currents. LVH was induced in rabbits by renal artery banding. Single ventricular myocytes from rabbits with LVH at 3 mo after renal artery banding demonstrated increased cell membrane capacitance, prolonged action potential duration, decreased inward rectifier K+ current density, and increased transient outward K+ current density compared with myocytes from age-matched controls. Additional rabbits were randomized at 3 mo after banding to treatment with either vehicle or captopril for an additional 3 mo. Myocytes from LVH rabbits treated with vehicle showed persistent membrane current abnormalities. However, myocytes isolated from LVH rabbits treated with captopril had normal cell membrane capacitance, action potential duration, and membrane current densities. Captopril had no direct effect on membrane currents of either control or LVH myocytes. These data support the hypothesis that the action potential prolongation and membrane current abnormalities of LVH are reversed by regression. Normalization of membrane currents probably explains the reduced vulnerability to ventricular arrhythmia observed in this LVH model after treatment with captopril.

Analysis of catecholamine effects in single atrial trabeculae of the frog heart

1977 ◽  
Vol 197 (1128) ◽  
pp. 333-362 ◽  
Keyword(s):  
Cell Membrane ◽  
Action Potential ◽  
Time Course ◽  
Drug Exposure ◽  
Drug Application ◽  
Latency Period ◽  
Frog Heart ◽  
Phosphodiesterase Activity ◽  
Inward Current ◽  
Calcium Inward Current

A study was made of the time course of the effects of adrenaline and isoprenaline on both twitch tension and the intracellular action potential of single atrial trabeculae from frog heart, under a variety of experimental conditions. Twitch tension and overshoot of action potentials rose and subsided in a parallel fashion during build-up and decline of catecholamine action. Cessation of stimulation during drug application had little effect on the tension responses to the drugs. These, and also results obtained with step changes of external calcium concentration during drug exposure, suggest that tension enhancement is a direct consequence of the increased calcium inward current produced by the catecholamines. Exceptional results from trabeculae of ‘hypodynamic’ hearts are described and interpreted on the basis of previous findings obtained in the ‘hypo-dynamic’ condition. Under suitable conditions, including the use of brief periods of drug exposure (≤20 s), three phases of ( β -catecholamine action were discernible: (1) a latency period, of up to 15 s, which preceded tension and potential rise after drug application. Results are presented suggesting that this latency mainly reflects the time which it takes for drug-combined receptors to activate adenylate cyclase in the cell membrane. (2) A sub­sequent phase was critically dependent, in both its magnitude and time course, on phosphodiesterase activity, as was shown by the application of the specific inhibitors papaverine, ICI 63 197, and Ro 20-1724. This phase is probably controlled by the build-up and decline of cAMP within the cells and the subsequent activation and deactivation of a protein kinase. (3) A third phase, associated with the final portion of the decline of catecholamine action, was relatively insensitive to moderate inhi­bition of phosphodiesterase activity. It is attributed to a change of phosphorylation of sites at the internal surface of the cell membrane, the process which, it is assumed, determines the size of calcium inward current during an action potential. Tension decline after a short staircase occurred with a time course closely similar to that of the final phase of the declining catecholamine response. A common final step in the sequential cellular processes under­ lying the two responses is proposed. In some 40% of the trabeculae examined, adrenaline responses were of ‘mixed’ origin: in addition to the relatively slow β -adrenergic action, an initial rapid tension change was present, and experimental tests suggest that this is mediated by α -type receptors.

scholarly journals Observations on the Fine Structure of the Turtle Atrium

1958 ◽  
Vol 4 (1) ◽  
pp. 63-72 ◽  
Author(s):  
Don W. Fawcett ◽  
Cecily C. Selby
Keyword(s):  
Fine Structure ◽  
Cell Membrane ◽  
Synaptic Vesicles ◽  
Myoneural Junction ◽  
Amorphous Component ◽  
Intercalated Discs ◽  
Particulate Form ◽  
Transitional Forms ◽  
Basic Similarity ◽  
Turtle Heart

The general fine structure of the atrial musculature of the turtle heart is described, including; the nature of the sarcolemma; the cross-banded structure of the myofibrils; the character of the sarcoplasm, and the form and disposition of its organelles. An abundant granular component of the sarcoplasm in this species is tentatively identified as a particulate form of glycogen. The myocardium is composed of individual cells joined end to end at primitive intercalated discs, and side to side at sites of cohesion that resemble the desmosomes of epithelia. Transitional forms are found between desmosomes and intercalated discs. Both consist of a thickened area of the cell membrane with an accumulation of dense material in the subjacent cytoplasm. This dense amorphous component is often continuous with the Z substance of the myofibrils and may be of the same composition. The observations reported reemphasize the basic similarity between desmosomes and terminal bars of epithelia and intercalated discs of cardiac muscle. Numerous unmyelinated nerves are found beneath the endocardium. Some of these occupy recesses in the surface of Schwann cells; others are naked axons. No specialized nerve endings are found. Axons passing near the sarcolemma contain synaptic vesicles, and it is believed that this degree of proximity is sufficient to constitute a functioning myoneural junction.

scholarly journals Calcium Ions and the Action Potential in Nitella

1962 ◽  
Vol 15 (1) ◽  
pp. 69 ◽  
Author(s):  
GP Findlay
Keyword(s):  
Cell Membrane ◽  
Action Potential ◽  
Electrical Activity ◽  
Calcium Ions ◽  
Current Flow ◽  
External Medium ◽  
Feedback Circuit ◽  
Predetermined Level ◽  
Voltage Clamping ◽  
Main Factor

Experiments are described in which a "voltage� clamping" technique has been applied to large ecorticate internodal cells of the freshwater alga Nitella. In this technique, a feedback circuit is used to change the potential difference between the vacuole of the cell and the external medium to some predetermined level and maintain it as close as possible to this level during the electrical activity of the cell. It is shown that the main factor in the phenomena of potential change and current flow, during the initial stages of the action potential in Nitella, is a tran-sient increase in the permeability of the cell membrane to calcium ions, and a consequent flow of these ions into the cell from the external medium.

scholarly journals A STUDY ON THE COUPLING MECHANISM BETWEEN ACTION POTENTIAL AND CONTRACTION IN THE FROG VENTRICLE

1969 ◽  
Vol 19 (4) ◽  
pp. 492-508 ◽  
Author(s):  
Hiroshi KAWATA ◽  
Jun-ichi SHIBATA ◽  
Masayosi GOTO
Keyword(s):  
Action Potential ◽  
Coupling Mechanism ◽  
Frog Ventricle

Energy cost of work in aerobic and anaerobic turtle heart muscle

1963 ◽  
Vol 205 (1) ◽  
pp. 17-22 ◽  
Author(s):  
Robert B. Reeves
Keyword(s):  
Heart Rate ◽  
Mechanical Performance ◽  
Atp Hydrolysis ◽  
Lactate Production ◽  
Work Rate ◽  
Perfusion Medium ◽  
Anaerobic Work ◽  
Perfused Hearts ◽  
Aerobic And Anaerobic ◽  
Turtle Heart

Aerobic rates of oxygen consumption and anaerobic rates of lactate production, each as a function of work rate at 23–25 C, were compared in 75 isolated perfused hearts from turtles ( Pseudemys scripta). Pressure-volume work at constant heart rate was varied over the range of 2–14 x 105 ergs/min. Control experiments established that turtle hearts are capable of sustained (greater than 15 hr) anaerobic work provided some plasma is present in the perfusion medium. Mechanical performance was unaffected by anoxia (pO2 < 2 mm Hg) except for some decrease in heart rate. Adenosine triphosphate (ATP) demand was the same at any given work rate whether the energy was supplied by oxidative phosphorylation or exclusively by anaerobic glycolysis. The efficiency of the heart, expressed as mechanical work divided by free energy consumed, was therefore independent of the metabolic pathways leading to production of ATP. If the Δ F' of ATP hydrolysis is taken to be 7.0 kcal/mole, the efficiency of the working turtle heart is 50 ± 3.4%.

Excitable properties and voltage-sensitive ion conductances of horizontal cells isolated from catfish (Ictalurus punctatus) retina

1986 ◽  
Vol 56 (1) ◽  
pp. 32-49 ◽  
Author(s):  
R. Shingai ◽  
B. N. Christensen
Keyword(s):  
Membrane Potential ◽  
Cell Membrane ◽  
Action Potential ◽  
Voltage Clamp ◽  
Ictalurus Punctatus ◽  
Horizontal Cells ◽  
Resting Potential ◽  
Patch Type ◽  
Voltage Range ◽  
Plateau Potential

External horizontal cells were enzymatically dissociated from intact catfish (Ictalurus punctatus) retina and pipetted onto a small chamber attached to the stage of an inverted phase-contrast microscope. Individual horizontal cells were recognized by their large size and restricted dendritic arborization. Low-resistance (3-12 M omega) patch-type electrodes were used to record intracellular potentials and to pass current across the cell membrane under either current or voltage-clamp conditions. The average resting potential of isolated horizontal cells was -67 V + 6.9 mV (mean +/- SD, n = 40). At the resting potential, the cell membrane appears to be mainly permeable to K. A depolarizing current step evoked an action potential in the cell. The maximum rate of rise of the action potential (dV/dt) in normal physiological solution was 6.5 +/- 1.8 V/s (means +/- SD, n = 24) and was reduced to 1.2 +/- 0.39 V/s (means +/- SD, n = 9) in 1-10 micron tetrodotoxin (TTX) and 3.2 +/- 1.4 V/s (means +/- SD, n = 6) in Ca-free solution. The maximum dV/dt was reduced in 10 mM extracellular K concentration [K]o to about half of that seen in standard saline, and values in 30 or 80 mM [K]o were similar to that measured in TTX. Following an action potential, the membrane potential reached a plateau potential of + 17.4 +/- 8.1 mV (means +/- SD, n = 17) and remained depolarized for variable periods of time lasting from less than a second to a few minutes. When the plateau potential was long lasting, the cell repolarized slowly and upon reaching zero rapidly repolarized to the original resting potential. The duration of the plateau potential decreased or was absent in saline containing one of the following calcium channel antagonists: La, Cd, Co, or Ni. The voltage-clamp technique was used to identify the membrane currents responsible for the membrane potential changes seen under current clamp. Experiments were carried out using either a single or two individual electrodes. Fast and steady-state inward currents were recorded from isolated horizontal cells in the voltage range between -20 and +20 mV. These currents were a result of increased membrane conductance to both Na and Ca ions. The Na channels are inactivated at depolarized potentials and are TTX sensitive. Ca channels are partially inactivated at depolarized potentials. The Ca conductance is decreased by Cd, Co, Ni, and La. Ba can substitute for Ca in the channel.(ABSTRACT TRUNCATED AT 400 WORDS)

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