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

Abstract

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 μM), lavendustin A (50 μM), and tyrphostin 23 (50 μM) stimulated I Ca by 132 ± 18% ( P < 0.001), 116 ± 18% ( P < 0.05), and 60 ± 6% ( P < 0.001), respectively. After I Castimulation by genistein, external application of isoproterenol (1 μM) 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.