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Subcellular Ca(2+)-gradients in A7r5 vascular smooth muscle
B Himpens1, H De Smedt, R Casteels
1Physiological Laboratory, KU Leuven, Belgium.
Cell Calcium
|January 1, 1994
Summary
Vasopressin (AVP) stimulation creates a calcium gradient in smooth muscle cells, with higher levels in the cytoplasm than the nucleus. This gradient is maintained even when calcium influx is blocked, showing distinct cellular calcium handling.
Area of Science:
- Cell Biology
- Physiology
- Biochemistry
Background:
- Calcium ions (Ca2+) play critical roles in cellular signaling.
- Differential distribution and regulation of intracellular calcium are essential for cell function.
- Understanding calcium dynamics in smooth muscle cells is key to understanding vascular tone and related diseases.
Purpose of the Study:
- To investigate the spatial and temporal dynamics of free calcium concentrations in the nucleus ([Ca2+]n) and cytoplasm ([Ca2+]c) of cultured A7r5 smooth muscle cells.
- To determine the influence of vasopressin (AVP) stimulation on these calcium gradients.
- To elucidate the roles of extracellular calcium and calcium influx pathways in regulating nuclear and cytosolic calcium levels.
Main Methods:
- Confocal laser microscopy was employed to measure intracellular calcium concentrations.
- The Ca(2+)-indicator Indo-1 was used for real-time monitoring of free calcium.
- A7r5 smooth muscle cells were stimulated with varying concentrations of vasopressin (AVP) in both calcium-containing and calcium-free solutions.
- Pharmacological agents like verapamil and Ni2+ were used to block calcium influx channels.
Main Results:
- Vasopressin (AVP) stimulation induced a calcium gradient with higher cytosolic calcium ([Ca2+]c) than nuclear calcium ([Ca2+]n), particularly at the subplasmalemmal region.
- This gradient ([Ca2+]c > [Ca2+]n) was sustained after the initial rise and was preserved even when extracellular calcium was removed or calcium influx was blocked.
- The agonist concentration influenced the differential calcium response, with lower AVP concentrations failing to establish the distinct cytosolic-nuclear gradient.
Conclusions:
- Cytosolic and nuclear calcium stores exhibit distinct behaviors in response to agonist stimulation.
- Calcium influx mechanisms significantly impact cytosolic calcium levels but have a lesser effect on nuclear calcium.
- The observed calcium gradients are dependent on agonist concentration, highlighting complex regulatory mechanisms in smooth muscle cells.