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L-type Ca2+ current in guinea pig ventricular myocytes treated with modulators of tyrosine phosphorylation
T Ogura1, L M Shuba, T F McDonald
1Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7.
Abstract:
Guinea pig ventricular myocytes in whole cell configuration were treated with tyrosine kinase (TK) inhibitors [genistein (Gst), tyrphostin A23 (T23), and tyrphostin A25 (T25)] and with inactive analogs [daidzein, genistin, and tyrphostin A1 (T1)] to measure effects on L-type Ca2+ current (ICa,L). Gst inhibited ICa,L (IC50 = 47 microM) without affecting its time course or shifting the ICa, L-voltage relationship. At the highest concentration of isoflavone tested (200 microM), ICa,L was inhibited by 66 +/- 7% (Gst), 22 +/- 2% (daidzein), and 1 +/- 3% (genistin). Inhibition of ICa,L by the active tyrphostins was significantly larger than inhibition by T1; at 200 microM the inhibitions were 72 +/- 6% (T23), 71 +/- 6% (T25), and 27 +/- 6% (T1). The phosphotyrosine phosphatase inhibitor orthovanadate (1 mM) had a small stimulatory effect (6 +/- 2%) on basal ICa,L and blocked the inhibition of ICa,L by TK inhibitors. The data suggest a role for the TK-phosphotyrosine phosphatase system in the regulation of cardiac Ca2+ channels.
Insights
Tyrosine kinase inhibitors like genistein significantly reduced L-type Ca2+ current in guinea pig heart cells. This suggests a role for tyrosine kinase and phosphatase systems in regulating cardiac calcium channels.
Area of Science:
- Cardiovascular Physiology
- Molecular Pharmacology
Background:
- L-type Ca2+ channels are crucial for cardiac function.
- The regulation of these channels by signaling pathways is not fully understood.
Purpose of the Study:
- To investigate the effect of tyrosine kinase (TK) inhibitors on L-type Ca2+ current (ICa,L) in guinea pig ventricular myocytes.
- To explore the involvement of the TK-phosphotyrosine phosphatase system in regulating cardiac Ca2+ channels.
Main Methods:
- Whole-cell patch-clamp electrophysiology was used to measure ICa,L.
- Guinea pig ventricular myocytes were treated with various TK inhibitors (genistein, tyrphostins) and their inactive analogs.
- The effect of orthovanadate, a phosphotyrosine phosphatase inhibitor, was also assessed.
Main Results:
- Genistein inhibited ICa,L with an IC50 of 47 microM.
- Active tyrphostins (T23, T25) caused significant inhibition of ICa,L (approx. 71-72%) at 200 microM.
- Inactive analogs showed minimal inhibition, and orthovanadate partially blocked TK inhibitor effects.
Conclusions:
- The tyrosine kinase-phosphotyrosine phosphatase system plays a regulatory role in cardiac L-type Ca2+ channels.
- Specific TK inhibitors demonstrate potential for modulating cardiac calcium currents.