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Tyrosine kinase and protein kinase C regulate L-type Ca(2+) current cooperatively in human atrial myocytes
C Boixel1, S Tessier, Y Pansard
1Institut National de la Santé et de la Recherche Médicale, Unité 460, Faculté de Médecine Xavier Bichat, Paris, France.
Abstract:
The effects of tyrosine protein kinases (TK) on the L-type Ca(2+) current (I(Ca)) were examined in whole cell patch-clamped human atrial myocytes. The TK inhibitors genistein (50 microM), lavendustin A (50 microM), and tyrphostin 23 (50 microM) stimulated I(Ca) by 132 +/- 18% (P < 0.001), 116 +/- 18% (P < 0.05), and 60 +/- 6% (P < 0.001), respectively. After I(Ca) stimulation by genistein, external application of isoproterenol (1 microM) caused an additional increase in I(Ca). Dialyzing the cells with a protein kinase A inhibitor suppressed the effect of isoproterenol on I(Ca) but not that of genistein. Inhibition of protein kinase C (PKC) by pretreatment of cells with 100 nM staurosporine or 100 nM calphostin C prevented the effects of genistein on I(Ca). The PKC activator phorbol 12-myristate 13-acetate (PMA), after an initial stimulation (75 +/- 17%, P < 0.05), decreased I(Ca) (-36 +/- 5%, P < 0.001). Once the inhibitory effect of PMA on I(Ca) had stabilized, genistein strongly stimulated the current (323 +/- 25%, P < 0.05). Pretreating myocytes with genistein reduced the inhibitory effect of PMA on I(Ca). We conclude that, in human atrial myocytes, TK inhibit I(Ca) via a mechanism that involves PKC.
Insights
Tyrosine protein kinases (TK) inhibit L-type calcium current (I(Ca)) in human atrial cells. This inhibition involves protein kinase C (PKC), highlighting a novel regulatory pathway for cardiac function.
Area of Science:
- Cardiovascular Physiology
- Molecular Cell Biology
- Biochemistry
Background:
- L-type calcium current (I(Ca)) is critical for cardiac excitation-contraction coupling.
- Tyrosine protein kinases (TK) are key regulators of cellular signaling pathways.
- The precise role of TK in modulating I(Ca) in human atrial myocytes remains incompletely understood.
Purpose of the Study:
- To investigate the effects of tyrosine protein kinases (TK) on L-type calcium current (I(Ca)) in human atrial myocytes.
- To elucidate the specific signaling pathways, particularly protein kinase C (PKC), involved in TK-mediated regulation of I(Ca).
Main Methods:
- Whole-cell patch-clamp electrophysiology was employed on human atrial myocytes.
- Specific TK inhibitors (genistein, lavendustin A, tyrphostin 23) were used to block TK activity.
- Protein kinase inhibitors (staurosporine, calphostin C) and activators (PMA) were utilized to probe PKC involvement.
Main Results:
- TK inhibitors significantly stimulated I(Ca), indicating an inhibitory role of TK.
- Inhibition of protein kinase C (PKC) abolished the stimulatory effect of TK inhibitors on I(Ca).
- PKC activation initially stimulated but then inhibited I(Ca), with subsequent TK inhibition reversing the inhibitory effect.
Conclusions:
- Tyrosine protein kinases (TK) exert an inhibitory influence on L-type calcium current (I(Ca)) in human atrial myocytes.
- This TK-mediated inhibition of I(Ca) is dependent on the activation of protein kinase C (PKC).
- These findings reveal a novel signaling cascade involving TK and PKC in the regulation of cardiac calcium influx.