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Isoform-specific protein kinase C activity at variable Ca2+ entry during coronary artery contraction by vasoactive
1Department of Physiology and Biophysics, and Center for Excellence in Cardiovascular-Renal Research, University of Mississippi Medical Center, Jackson 39216-4505, USA.
Canadian Journal of Physiology and Pharmacology
|May 18, 1999
Summary
Vasoactive eicosanoids cause coronary vasospasms through protein kinase C (PKC) activation. This study reveals distinct roles for Ca2+-independent epsilon-PKC and Ca2+-dependent alpha-PKC in mediating these contractions.
Area of Science:
- Cardiovascular Physiology
- Molecular Pharmacology
- Smooth Muscle Biology
Background:
- Vasoactive eicosanoids contribute to coronary vasospasms.
- The precise signaling pathways, particularly the role of protein kinase C (PKC) isoforms, in eicosanoid-induced coronary vasoconstriction remain incompletely understood.
- The influence of calcium (Ca2+) influx on specific PKC isoform activity in coronary smooth muscle is largely unknown.
Purpose of the Study:
- To investigate the relationship between extracellular calcium concentrations, eicosanoid stimulation, and protein kinase C (PKC) activity in porcine coronary artery smooth muscle.
- To elucidate the specific PKC isoforms involved in eicosanoid-induced coronary vasoconstriction and their dependence on Ca2+ influx.
- To determine the impact of varying Ca2+ levels on PKC translocation and its correlation with isometric contraction.
Main Methods:
- Porcine coronary artery strips were used to measure 45Ca2+ influx and isometric contraction.
- Experiments were conducted at increasing extracellular calcium concentrations ([Ca2+]e) and stimulated with prostaglandin F2alpha (PGF2alpha) or U46619.
- Cytosolic and particulate fractions were analyzed for PKC activity and isoform-specific translocation using Western blotting.
Main Results:
- Eicosanoid stimulation increased PKC activity and contraction even at low [Ca2+]e, without significant Ca2+ influx, implicating Ca2+-independent PKC isoforms like epsilon-PKC.
- At higher [Ca2+]e, both Ca2+ influx and contraction increased, correlating with maximal PKC activity and translocation of alpha-PKC, suggesting a Ca2+-dependent component.
- A threshold of approximately 7 micromol x kg(-1) x min(-1) 45Ca2+ influx was observed for maximal PKC activation, with further increases in Ca2+ influx leading to greater contraction despite reduced PKC activity.
Conclusions:
- Eicosanoid-induced coronary contraction involves a significant Ca2+-independent component mediated by epsilon-PKC translocation.
- A Ca2+-dependent component, involving alpha-PKC translocation, contributes to contraction at submaximal Ca2+ influx levels.
- These findings highlight the differential roles of PKC isoforms in regulating coronary smooth muscle tone in response to vasoactive eicosanoids.
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