scholarly journals The Effects of External Sodium and Potassium Concentration on the Membrane Potential of Atrioventricular Fibers of the Toad

1966 ◽  
Vol 50 (2) ◽  
pp. 243-253 ◽  
Author(s):  
Tomio Kanno ◽  
Kojiro Matsuda
Keyword(s):  
Action Potentials ◽  
Potassium Concentration ◽  
Resting Potential ◽  
Conducting System ◽  
Ringer’S Solution ◽  
Spontaneous Action ◽  
V Region ◽  
Spontaneous Action Potentials ◽  
Sodium And Potassium ◽  
Peak Value

Intracellular records were made from fibers in the A-V conducting system of isolated toad hearts. The A-V region was perfused with Ringer's solution of various K and Na concentrations. Resting potential in 2.8 mM [K]o was about 60 mv. Over the range 0.28 to 28 mM, resting potential diminished with increasing [K]o. Spontaneous action potentials appeared when [K]o was increased to 11.2 mM, and when resting potential had fallen to about 40 to 50 mv. Changes in [Na]o over the range 22 to 110 mM had a little effect on resting potential, but there was a linear relation between the peak value of the action potential and log [Na]o Wenckebach periodicity was observed when [Na]o was lowered.

Vascular muscle cell depolarization and activation in renal arteries on elevation of transmural pressure

1987 ◽  
Vol 253 (4) ◽  
pp. F778-F781 ◽  
Author(s):  
D. R. Harder ◽  
R. Gilbert ◽  
J. H. Lombard
Keyword(s):  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Muscle Cell ◽  
Action Potentials ◽  
Transmural Pressure ◽  
Renal Arteries ◽  
Resting Potential ◽  
Internal Diameter ◽  
Spontaneous Action ◽  
Spontaneous Action Potentials

The goal of this study was to define some of the cellular and ionic mechanisms of smooth muscle cell activation in dog renal arteries exposed to physiological levels of transmural pressure. Isolated interlobular arteries were cannulated and connected to a pressure reservoir to allow manipulation of transmural pressure in 20-mmHg increment steps from 20 to 120 mmHg. As transmural pressure was increased, vascular smooth muscle exhibited a linear depolarization from an average resting potential of -57+/- 2 mV at 20 mmHg to -38+/- 2.4 mV at 120 mmHg. Spontaneous action potentials could often be recorded at pressures greater than 80 mmHg. These appeared to occur primarily at bifurcation points of branching arteries. Vascular smooth muscle depolarization and action potentials occurring in response to increases in transmural pressure were associated with a maintenance of internal diameter of the vessel segments despite increases in transmural pressure in the range between 60 and 120 mmHg. The “pressure-induced” activation of vascular smooth muscle contraction and spontaneous action potentials of small renal arteries at higher transmural pressures were blocked on Ca2+ channel inhibition with verapamil (10(-6) M). These data document a membrane ionic mechanism (probably increased Ca2+ influx) for pressure-induced myogenic activation of isolated renal arteries. It is interesting that the contraction of these vessels occurs over the pressure range in which autoregulation of renal blood flow normally occurs. The physiological significance of these responses needs to be determined.

scholarly journals Mechanisms Underlying Spontaneous Action Potential Generation Induced by Catecholamine in Pulmonary Vein Cardiomyocytes: A Simulation Study

2019 ◽  
Vol 20 (12) ◽  
pp. 2913 ◽  
Author(s):  
Shohei Umehara ◽  
Xiaoqiu Tan ◽  
Yosuke Okamoto ◽  
Kyoichi Ono ◽  
Akinori Noma ◽  
...  
Keyword(s):  
Action Potentials ◽  
Ryanodine Receptors ◽  
Pulmonary Veins ◽  
Resting Potential ◽  
Ip3 Receptors ◽  
Spontaneous Action Potential ◽  
Spontaneous Action ◽  
Positive And Negative Feedback ◽  
Time Courses ◽  
Spontaneous Action Potentials

Cardiomyocytes and myocardial sleeves dissociated from pulmonary veins (PVs) potentially generate ectopic automaticity in response to noradrenaline (NA), and thereby trigger atrial fibrillation. We developed a mathematical model of rat PV cardiomyocytes (PVC) based on experimental data that incorporates the microscopic framework of the local control theory of Ca2+ release from the sarcoplasmic reticulum (SR), which can generate rhythmic Ca2+ release (limit cycle revealed by the bifurcation analysis) when total Ca2+ within the cell increased. Ca2+ overload in SR increased resting Ca2+ efflux through the type II inositol 1,4,5-trisphosphate (IP3) receptors (InsP3R) as well as ryanodine receptors (RyRs), which finally triggered massive Ca2+ release through activation of RyRs via local Ca2+ accumulation in the vicinity of RyRs. The new PVC model exhibited a resting potential of −68 mV. Under NA effects, repetitive Ca2+ release from SR triggered spontaneous action potentials (APs) by evoking transient depolarizations (TDs) through Na+/Ca2+ exchanger (APTDs). Marked and variable latencies initiating APTDs could be explained by the time courses of the α1- and β1-adrenergic influence on the regulation of intracellular Ca2+ content and random occurrences of spontaneous TD activating the first APTD. Positive and negative feedback relations were clarified under APTD generation.

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