scholarly journals The resting membrane potential of hSC-CM in a syncytium is more hyperpolarised than that of isolated cells

Channels ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 239-252
Author(s):  
Dieter V. Van de Sande ◽  
Ivan Kopljar ◽  
Alaerts Maaike ◽  
Ard Teisman ◽  
David J. Gallacher ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Resting Membrane Potential ◽  
Isolated Cells

scholarly journals Control of ion distribution in isolated smooth muscle cells. I. Potassium.

1980 ◽  
Vol 75 (2) ◽  
pp. 163-182 ◽  
Author(s):  
C R Scheid ◽  
F S Fay
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Smooth Muscle Cells ◽  
Muscle Cells ◽  
Resting Membrane Potential ◽  
Stomach Muscle ◽  
Isolated Cells ◽  
Intracellular Space ◽  
Ion Movements ◽  
Isolated Smooth Muscle Cells

We describe a technique for examining unidirectional ion movements in suspensions of enzymatically disaggregated smooth muscle cells derived from stomach muscle of the toad. This technique has been used to analyze the movement of 42K across these cells. This analysis was greatly simplified by the finding that the cells were in a steady state with respect to K+ distribution after isolation. The potassium contents of the isolated cells were identical to those of intact smooth muscle (131 mM/liter intracellular fluid) and stable for over 4 h; moreover, the unidirectional influx and efflux rates were equal. An additional simplification was provided by the finding that virtually all the K+ exchanges in a manner predicted for a simple two-compartment system consisting of an extracellular and an intracellular space. Transmembrane K+ flux in these cells averaged 1.2 pmol.cm-2.s-1 at room temperature. A large portion (approximately 80%) of 42K influx appeared to be mediated by a saturable transport system with an apparent Km of 0.6 mM and an apparent Vmax of 1.3 pmol.cm-2.s-1. The calculated resting membrane permeability to K+ in these isolated smooth muscle cells, assuming a membrane potential of -50 mV, was 2.9 X 10(-8) cm/s. The calculated gK+ was 2.7 mumho/cm2 constituting only a small fraction of the total membrane conductance as measured electrophysiologically. The latter finding suggests that the resting membrane potential in the isolated cells must be determined by ions in addition to K+. We propose that these methods for studying ion movements in smooth muscle should aid in unraveling the mechanisms responsible for controlling the distribution of ions both at rest, as in the present study, as well as in response to neurotransmitters.

scholarly journals Exercise training increases K+-channel contribution to regulation of coronary arterial tone

1998 ◽  
Vol 84 (4) ◽  
pp. 1225-1233 ◽  
Author(s):  
D. K. Bowles ◽  
M. H. Laughlin ◽  
M. Sturek
Keyword(s):  
Membrane Potential ◽  
Exercise Training ◽  
Sodium Nitroprusside ◽  
K Channel ◽  
Resting Membrane Potential ◽  
Channel Blockers ◽  
Miniature Swine ◽  
Isolated Cells ◽  
Resting Tension ◽  
Basal Tone

The present study examined whether regulation of coronary tone in conduit arteries (>1.0 mm ID) is altered by exercise training. Yucatan miniature swine were treadmill trained for 16–20 wk (Ex) and compared with sedentary counterparts (Sed). Endothelium-denuded arterial rings were stretched to optimal length and allowed to equilibrate for 60 min. Inhibition of either Ca2+-activated channels [1 mM tetraethylammonium (TEA) or 10 nM iberiotoxin (IBTX)] or voltage-dependent K+ channels [1 mM 4-aminopyridine (4-AP)] significantly increased resting tension in both groups; however, the effect of all K+-channel blockers was greater in Ex. Addition of 1 mM sodium nitroprusside reduced resting tension in both groups, confirming the presence of active basal tone; however, sodium nitroprusside-sensitive tone was increased approximately twofold in Ex compared with Sed group. Perforated patch-clamp experiments on isolated smooth muscle cells demonstrated no effect of exercise training on whole cell TEA-sensitive, 4-AP-sensitive, or basal K+ current. Similarly, whereas TEA, 4-AP, and IBTX all decreased resting membrane potential, there was no difference in depolarization between groups. The greater effect of TEA on resting tension in Ex could be mimicked in Sed by addition of the Ca2+-channel agonist BAY K 8644. In conclusion, the greater response to K+-channel blockers after exercise training is consistent with an increased contribution of K+ channels to regulation of basal tone in conduit coronary arteries. The lack of an effect of training on K+ current characteristics or membrane potential responses in isolated cells suggests that a requisite factor for enhanced K+-channel activation in arteries from Ex, possibly stretch, is absent in isolated cells.

Effect of low chloride on relaxation in hamster diaphragm muscle

1986 ◽  
Vol 61 (1) ◽  
pp. 180-184 ◽  
Author(s):  
S. A. Esau ◽  
N. Sperelakis
Keyword(s):  
Membrane Potential ◽  
Muscle Fatigue ◽  
Time Constant ◽  
Diaphragm Muscle ◽  
Resting Membrane Potential ◽  
Krebs Solution ◽  
Sarcolemmal Membrane ◽  
Cl Conductance

With muscle fatigue the chloride (Cl-) conductance of the sarcolemmal membrane decreases. The role of lowered Cl- conductance in the prolongation of relaxation seen with fatigue was studied in isolated hamster diaphragm strips. The muscles were studied in either a Krebs solution or a low Cl- solution in which half of the NaCl was replaced by Na-gluconate. Short tetanic contractions were produced by a 160-ms train of 0.2-ms pulses at 60 Hz from which tension (T) and the time constant of relaxation were measured. Resting membrane potential (Em) was measured using KCl-filled microelectrodes with resistances of 15–20 M omega. Mild fatigue (20% fall in tension) was induced by 24–25 tetanic contractions at the rate of 2/s. There was no difference in Em or T in the two solutions, either initially or with fatigue. The time constant of relaxation was greater in low Cl- solution, both initially (22 +/- 3 vs. 18 +/- 5 ms, mean +/- SD, P less than 0.05) and with fatigue (51 +/- 18 vs. 26 +/- 7 ms, P less than 0.005). Lowering of sarcolemmal membrane Cl- conductance appears to play a role in the slowing of relaxation of hamster diaphragm muscle seen with fatigue.

Calcium channels and excitation–contraction coupling in cardiac cells. I. Two components of contraction in guinea-pig papillary muscle

1987 ◽  
Vol 65 (9) ◽  
pp. 1821-1831 ◽  
Author(s):  
E. Honoré ◽  
M. M. Adamantidis ◽  
B. A. Dupuis ◽  
C. E. Challice ◽  
P. Guilbault
Keyword(s):  
Membrane Potential ◽  
Guinea Pig ◽  
Papillary Muscle ◽  
Cardiac Cells ◽  
Resting Membrane Potential ◽  
Tonic Component ◽  
Contraction Coupling ◽  
Rich Solution ◽  
The Relationship ◽  
Guinea Pig Atria

Biphasic contractions have been obtained in guinea-pig papillary muscle by inducing partial depolarization in K+-rich solution (17 mM) containing 0.3 μM isoproterenol; whereas in guinea-pig atria, the same conditions led to monophasic contractions corresponding to the first component of contraction in papillary muscle. The relationships between the amplitude of the two components of the biphasic contraction and the resting membrane potential were sigmoidal curves. The first component of contraction was inactivated for membrane potentials less positive than those for the second component. In Na+-low solution (25 mM), biphasic contraction became monophasic subsequent to the loss of the second component, but tetraethylammonium unmasked the second component of contraction. The relationship between the amplitude of the first component of contraction and the logarithm of extracellular Ca2+ concentration was complex, whereas for the second component it was linear. When Ca2+ ions were replaced by Sr2+ ions, only the second component of contraction was observed. It is suggested that the first component of contraction may be triggered by a Ca2+ release from sarcoplasmic reticulum, induced by the fast inward Ca2+ current and (or) by the depolarization. The second component of contraction may be due to a direct activation of contractile proteins by Ca2+ entering the cell along with the slow inward Ca2+ current and diffusing through the sarcoplasm. These results do not exclude the existence of a third "tonic" component, which could possibly be mixed with the second component of contraction.

scholarly journals Activation of Ca(2+)-dependent K+ current by acetylcholine and histamine in a human gastric epithelial cell line.

1993 ◽  
Vol 102 (4) ◽  
pp. 667-692 ◽  
Author(s):  
E Hamada ◽  
T Nakajima ◽  
S Ota ◽  
A Terano ◽  
M Omata ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Epithelial Cell ◽  
Cell Line ◽  
K Channel ◽  
Resting Membrane Potential ◽  
Induced Response ◽  
Epithelial Cell Line ◽  
Bathing Solution ◽  
Pipette Solution ◽  
K Current

The effects of acetylcholine (ACh) and histamine (His) on the membrane potential and current were examined in JR-1 cells, a mucin-producing epithelial cell line derived from human gastric signet ring cell carcinoma. The tight-seal, whole cell clamp technique was used. The resting membrane potential, the input resistance, and the capacitance of the cells were approximately -12 mV, 1.4 G ohms, and 50 pF, respectively. Under the voltage-clamp condition, no voltage-dependent currents were evoked. ACh or His added to the bathing solution hyperpolarized the membrane by activating a time- and voltage-independent K+ current. The ACh-induced hyperpolarization and K+ current persisted, while the His response desensitized quickly (< 1 min). These effects of ACh and His were mediated predominantly by m3-muscarinic and H1-His receptors, respectively. The K+ current induced by ACh and His was inhibited by charybdotoxin, suggesting that it is a Ca(2+)-activated K+ channel current (IK.Ca). The measurement of intracellular Ca2+ ([Ca2+]i) using Indo-1 revealed that both agents increased [Ca2+]i with similar time courses as they increased IK.Ca. When EGTA in the pipette solution was increased from 0.15 to 10 mM, the induction of IK.Ca by ACh and His was abolished. Thus, both ACh and His activate IK.Ca by increasing [Ca2+]i in JR-1 cells. In the Ca(2+)-free bathing solution (0.15 mM EGTA in the pipette), ACh evoked IK.Ca transiently. Addition of Ca2+ (1.8 mM) to the bath immediately restored the sustained IK.Ca. These results suggest that the ACh response is due to at least two different mechanisms; i.e., the Ca2+ release-related initial transient activation and the Ca2+ influx-related sustained activation of IK.Ca. Probably because of desensitization, the Ca2+ influx-related component of the His response could not be identified. Intracellularly applied inositol 1,4,5-trisphosphate (IP3), with and without inositol 1,3,4,5-tetrakisphosphate (IP4), mimicked the ACh response. IP4 alone did not affect the membrane current. Under the steady effect of IP3 or IP3 plus IP4, neither ACh nor His further evoked IK.Ca. Intracellular application of heparin or of the monoclonal antibody against the IP3 receptor, mAb18A10, inhibited the ACh and His responses in a concentration-dependent fashion. Neomycin, a phospholipase C (PLC) inhibitor, also inhibited the agonist-induced response in a concentration-dependent fashion. Although neither pertussis toxin (PTX) nor N-ethylmaleimide affected the ACh or His activation of IK,Ca, GDP beta S attenuated and GTP gamma S enhanced the agonist response.(ABSTRACT TRUNCATED AT 400 WORDS)

The resting membrane potential of white muscle from brown trout (Salmo trutta) exposed to copper in soft, acidic water

2000 ◽  
Vol 203 (14) ◽  
pp. 2229-2236 ◽  
Author(s):  
M.W. Beaumont ◽  
E.W. Taylor ◽  
P.J. Butler
Keyword(s):  
Membrane Potential ◽  
Brown Trout ◽  
Salmo Trutta ◽  
White Muscle ◽  
Low Ph ◽  
Ammonium Ion ◽  
Muscle Membrane ◽  
Resting Membrane Potential ◽  
Muscle Fibres ◽  
Brown Trout Salmo Trutta

Previously, the distribution of ammonia between the intracellular and extracellular compartments has been used to predict a significant depolarisation of the resting membrane potential (E(M)) of white muscle from brown trout (Salmo trutta) exposed to a sub-lethal combination of copper and low pH. However, this prediction is based upon two assumptions (i) a relatively high membrane permeability for the ammonium ion with respect to that for ammonia gas and (ii) that this is unaltered by exposure to copper and low pH. Since there is conflicting evidence in the literature of the validity of these assumptions, in the present study E(M) was directly measured in white muscle fibres of trout exposed to copper and low pH (E(M)=−52.2+/−4.9 mV) and compared with that of unexposed, control animals (E(M)=−86.5+/−2.9 mV) (means +/− s.e.m., N=6). In confirming the predicted depolarisation, these data support the hypothesis of electrophysiological impairment as a factor in the reduction in the swimming performance of trout exposed to these pollutants. In addition, the results of this study support the role of a significant permeability of the muscle membrane to NH(4)(+) in determining the distribution of ammonia in fish.

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