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Insulin attenuates agonist-evoked calcium transients in vascular smooth muscle cells
R M Touyz1, B Tolloczko, E L Schiffrin
1Clinical Research Institute of Montreal, University of Montreal, Quebec, Canada.
Abstract:
Insulin may decrease the contractile response of vascular smooth muscle to vasoactive agents. This could be due to interactions of insulin with the effects of vasoactive agonists on intracellular free calcium transients in vascular smooth muscle cells. This study assesses the effects of physiological doses of insulin (70 microU/mL) on calcium responses in cultured vascular smooth muscle cells (primary unpassaged and passaged) to angiotensin II (1 nmol/L), arginine vasopressin (10 nmol/L), and norepinephrine (10 mumol/L). Intracellular free Ca2+ concentrations in single cells were measured microphotometrically using fura 2-AM. Insulin, angiotensin II, arginine vasopressin, and norepinephrine significantly increased calcium (to 115 +/- 7, 183 +/- 20, 184 +/- 15, and 168 +/- 12 nmol/L, respectively, from basal calcium of 90 +/- 10 nmol/L). Insulin significantly attenuated the agonist-induced calcium responses. The effects of insulin were almost completely inhibited by diltiazem, staurosporine, calphostin C, and thapsigargin. In conclusion, insulin stimulates calcium transients but blunts agonist-mediated calcium rises in vascular smooth muscle cells. These responses are related to regulatory effects of insulin on cellular calcium homeostasis and may explain how insulin modulates vascular smooth muscle contraction.
Insights
Insulin affects vascular smooth muscle cells by stimulating calcium transients but blunting responses to vasoactive agents. This modulation of cellular calcium homeostasis may explain insulin's role in regulating vascular contraction.
Area of Science:
- Vascular Biology
- Cell Physiology
- Endocrinology
Background:
- Insulin's effect on vascular smooth muscle contraction is partly mediated by intracellular calcium.
- Vasoactive agents like angiotensin II, arginine vasopressin, and norepinephrine influence vascular tone via calcium signaling.
Purpose of the Study:
- To investigate the impact of physiological insulin doses on intracellular calcium responses in vascular smooth muscle cells.
- To determine how insulin modulates calcium transients induced by common vasoactive agonists.
Main Methods:
- Primary and passaged vascular smooth muscle cells were cultured.
- Intracellular free calcium concentrations were measured using microphotometry with fura 2-AM.
- Cells were exposed to insulin and various vasoactive agents (angiotensin II, arginine vasopressin, norepinephrine).
Main Results:
- Insulin, angiotensin II, arginine vasopressin, and norepinephrine all significantly increased intracellular calcium levels.
- Insulin significantly attenuated the calcium increases induced by the vasoactive agonists.
- These insulin effects were largely inhibited by diltiazem, staurosporine, calphostin C, and thapsigargin.
Conclusions:
- Insulin stimulates basal calcium transients but attenuates agonist-induced calcium rises in vascular smooth muscle cells.
- Insulin's modulation of vascular smooth muscle calcium responses is linked to cellular calcium homeostasis regulation.
- These findings provide insight into insulin's mechanism for modulating vascular smooth muscle contraction.