Related Experiment Videos
Increased myofibrillar protein phosphatase-1 activity impairs rat aortic smooth muscle activation after hypoxia
Hwee Teoh1, Mary Zacour, Avraham D Wener
1Terrence Donnelly Laboratories, Division of Respirology and Department of Critical Care, St. Michael's Hospital, University of Toronto, Toronto, Ontario, Canada M5B 1W8.
Abstract:
We hypothesized that increased myofibrillar type 1 protein phosphatase (PP1) catalytic activity contributes to impaired aortic smooth muscle contraction after hypoxia. Our results show that inhibition of PP1 activity with microcystin-LR (50 nmol/l) or okadaic acid (100 nmol/l) increased phenylephrine- and KCl-induced contraction to a greater extent in aortic rings from rats exposed to hypoxia (10% O(2)) for 48 h than in rings from normoxic animals. PP1 inhibition also restored the level of phosphorylation of the 20-kDa myosin light chain (LC(20)) during maximal phenylephrine-induced contraction to that observed in the normoxic control group. Myofibrillar PP1 activity was greater in aortas from rats exposed to hypoxia than in normoxic rats (P < 0.05). Levels of the protein myosin phosphatase-targeting subunit 1 (MYPT1) that mediates myofibrillar localization of PP1 activity were increased in aortas from hypoxic rats (193 +/- 28% of the normoxic control value, P < 0.05) and in human aortic smooth muscle cells after hypoxic (1% O(2)) incubation (182 +/- 18% of the normoxic control value, P < 0.05). Aortic levels of myosin light chain kinase were similar in normoxic and hypoxic groups. In conclusion, after hypoxia, increased MYPT1 protein and myofibrillar PP1 activity impair aortic vasoreactivity through enhanced dephosphorylation of LC(20).
Insights
Hypoxia impairs aortic smooth muscle contraction by increasing myofibrillar protein phosphatase 1 (PP1) activity. This leads to enhanced dephosphorylation of myosin light chain 20 (LC(20)), reducing vasoreactivity.
Area of Science:
- Cardiovascular Physiology
- Smooth Muscle Biology
- Hypoxia Research
Background:
- Hypoxia is known to affect vascular smooth muscle function.
- Impaired contraction in aortic smooth muscle after hypoxia requires further investigation into underlying molecular mechanisms.
Purpose of the Study:
- To investigate the role of myofibrillar protein phosphatase 1 (PP1) catalytic activity in impaired aortic smooth muscle contraction following hypoxia.
- To determine the impact of PP1 activity on myosin light chain phosphorylation and vasoreactivity after hypoxic exposure.
Main Methods:
- Aortic rings from rats exposed to hypoxia (10% O(2)) or normoxia were used.
- PP1 activity was inhibited using microcystin-LR or okadaic acid.
- Phenylephrine- and KCl-induced contractions were measured.
- Myosin light chain 20 (LC(20)) phosphorylation and myosin phosphatase-targeting subunit 1 (MYPT1) levels were assessed.
Main Results:
- Inhibition of PP1 activity enhanced phenylephrine- and KCl-induced contractions more in hypoxic rat aortic rings than in normoxic controls.
- PP1 inhibition restored LC(20) phosphorylation levels in hypoxic aortic rings to normoxic levels.
- Myofibrillar PP1 activity and MYPT1 protein levels were significantly increased in aortas from hypoxic rats and human aortic smooth muscle cells.
Conclusions:
- Increased MYPT1 protein and myofibrillar PP1 activity contribute to impaired aortic vasoreactivity after hypoxia.
- Enhanced dephosphorylation of LC(20) by PP1 is a key mechanism underlying hypoxia-induced impairment of aortic smooth muscle contraction.