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Regulation of calcium channel current in A7r5 vascular smooth muscle cells by cyclic nucleotides
J N Lorenz1, D R Bielefeld, N Sperelakis
1Department of Physiology and Biophysics, University of Cincinnati College of Medicine, Ohio 45267.
Abstract:
In vascular smooth muscle (VSM) cells, the slow inward calcium current (ICa) may be regulated by phosphorylation of the calcium channel protein or of associated regulatory proteins. We investigated the role of several protein kinase systems in the regulation of ICa in cultured A7r5 cells, a clonal cell line derived from rat aorta. The perforated-patch voltage-clamp technique was used to record whole cell ICa. To isolate the ICa, the pipette contained high Cs+ and the bath contained 140 mM tetraethylammonium to block potassium currents. Ba2+ was used as the charge carrier. In control experiments, ICa was stable for at least 15 min. Compared with 23 +/- 3% in the time-control group (i.e., run-down; n = 10), 3 mM 8-bromo-adenosine 3',5'-cyclic monophosphate (8-BrcAMP) inhibited peak ICa by 53 +/- 3% (n = 9) within 15 min. Similarly, 3 mM 8-bromo-guanosine 3',5'-cyclic monophosphate (8-BrcGMP) inhibited ICa by 59 +/- 4 (n = 11). Application of 30 microM forskolin inhibited ICa by 58 +/- 9% (n = 6) within 5 min (compared with 4 +/- 3% for the 5-min time control). Forskolin also shifted the reversal potential to the left, suggesting a stimulation of an outward current. In the presence of the protein kinase inhibitor, 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, the same dose of forskolin had no effect (n = 7). The water-soluble analogue of forskolin (L-858051, 30 microM) decreased ICa by 72 +/- 11% (n = 9) and reduced the outward current component.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Cyclic nucleotides like 8-bromo-cAMP and 8-bromo-cGMP, along with forskolin, inhibit calcium currents (ICa) in vascular smooth muscle cells. Protein kinase inhibition blocks forskolin
Area of Science:
- Cardiovascular Physiology
- Molecular Pharmacology
Background:
- Vascular smooth muscle (VSM) cells regulate blood pressure via calcium currents.
- Phosphorylation of calcium channels may modulate VSM cell activity.
Purpose of the Study:
- To investigate the role of protein kinase systems in regulating the slow inward calcium current (ICa) in cultured rat aortic smooth muscle cells (A7r5).
Main Methods:
- Utilized the perforated-patch voltage-clamp technique to record whole-cell ICa in A7r5 cells.
- Isolated ICa using high Cs+ in the pipette and tetraethylammonium in the bath, with Ba2+ as the charge carrier.
- Administered cyclic nucleotide analogues (8-BrcAMP, 8-BrcGMP), forskolin, and a protein kinase inhibitor.
Main Results:
- 8-BrcAMP and 8-BrcGMP significantly inhibited peak ICa by 53% and 59%, respectively.
- Forskolin inhibited ICa by 58% and also affected the reversal potential, suggesting outward current modulation.
- A protein kinase inhibitor abolished the forskolin-induced inhibition of ICa.
Conclusions:
- Cyclic nucleotide-dependent protein kinases play a significant role in regulating ICa in VSM cells.
- Forskolin's effects on ICa are mediated through protein kinase activation.
- These findings suggest a signaling pathway involving cyclic nucleotides and protein kinases in VSM calcium channel regulation.