Tyrosine kinase and protein kinase C regulate L-type Ca2+ current cooperatively in human atrial myocytes

The effects of tyrosine protein kinases (TK) on the L-type Ca2+ current (I-Ca) were examined in whole cell patch-clamped human atrial myocytes. The TK inhibitors genistein (50 mu M), lavendustin A (50 mu M), and tyrphostin 23 (50 mu M) 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 mu M) 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%, Pt 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.