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Published on: September 22, 2011
Calcium dynamics underlying the myogenic response of the renal afferent arteriole
Aurélie Edwards1, Anita T Layton
1Dept. of Mathematics, Duke Univ., Box 90320, Durham, NC 27708-0320. alayton@math.duke.edu.
Insights
The myogenic response in renal afferent arterioles involves complex intracellular calcium signaling. A mathematical model reveals how ion channel activity and calcium dynamics regulate blood pressure stabilization, particularly during hypertension.
Area of Science:
- Physiology
- Biophysics
- Computational Biology
Background:
- The myogenic response of renal afferent arterioles is crucial for regulating glomerular filtration rate and protecting glomeruli from pressure surges, especially in hypertension.
- This response involves increased muscle tone and decreased diameter in response to elevated blood pressure.
- Understanding the underlying molecular mechanisms is essential for managing renal blood flow and pressure.
Purpose of the Study:
- To develop a mathematical model of intracellular calcium (Ca2+) signaling in afferent arteriole smooth muscle cells.
- To investigate the mechanisms governing the myogenic response, particularly the role of pressure-induced changes in nonselective cation channels.
- To simulate and analyze the dynamics of Ca2+ signaling, channel activity, and cell mechanics.
Main Methods:
- Development of a detailed mathematical model of a smooth muscle cell in the renal afferent arteriole.
- Incorporation of transmembrane ionic transport, intracellular Ca2+ dynamics, and myosin light chain phosphorylation kinetics.
- Simulation of cell mechanical behavior and response to various pharmacological interventions and pressure changes.
Main Results:
- The model predicts spontaneous vasomotion at physiological pressures, mimicking experimental observations.
- Simulated KCl and diltiazem treatments produced diameter changes consistent with in vitro findings.
- Oscillations result from Ca2+ exchange between cytosol and sarcoplasmic reticulum, modulated by KCa, ClCa, and L-type channels.
- Blocking specific channels or pumps abolished these oscillations, highlighting their critical roles.
Conclusions:
- The myogenic response profile is significantly influenced by ClCa and L-type channel conductance, and plasmalemmal Ca2+ pump activity.
- Inhibition of KCa channels is not required for myogenic contraction.
- Model suggests L-type channel kinetics lead to faster constriction than dilation, aligning with experimental data.
Abstract:
The renal afferent arteriole reacts to an elevation in blood pressure with an increase in muscle tone and a decrease in luminal diameter. This effect, known as the myogenic response, is believed to stabilize glomerular filtration and to protect the glomerulus from systolic blood pressure increases, especially in hypertension. To study the mechanisms underlying the myogenic response, we developed a mathematical model of intracellular Ca(2+) signaling in an afferent arteriole smooth muscle cell. The model represents detailed transmembrane ionic transport, intracellular Ca(2+) dynamics, the kinetics of myosin light chain phosphorylation, and the mechanical behavior of the cell. It assumes that the myogenic response is initiated by pressure-induced changes in the activity of nonselective cation channels. Our model predicts spontaneous vasomotion at physiological luminal pressures and KCl- and diltiazem-induced diameter changes comparable to experimental findings. The time-periodic oscillations stem from the dynamic exchange of Ca(2+) between the cytosol and the sarcoplasmic reticulum, coupled to the stimulation of Ca(2+)-activated potassium (KCa) and chloride (ClCa) channels, and the modulation of voltage-activated L-type channels; blocking sarco/endoplasmic reticulum Ca(2+) pumps, ryanodine receptors (RyR), KCa, ClCa, or L-type channels abolishes these oscillations. Our results indicate that the profile of the myogenic response is also strongly dependent on the conductance of ClCa and L-type channels, as well as the activity of plasmalemmal Ca(2+) pumps. Furthermore, inhibition of KCa is not necessary to induce myogenic contraction. Lastly, our model suggests that the kinetic behavior of L-type channels results in myogenic kinetics that are substantially faster during constriction than during dilation, consistent with in vitro observations (Loutzenhiser R, Bidani A, Chilton L. Circ. Res. 90: 1316-1324, 2002).
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