Ca-dependent facilitation of cardiac Ca current is due to Ca-calmodulin- dependent protein kinase

W. Yuan, Donald M Bers

Research output: Contribution to journalArticlepeer-review

198 Scopus citations


Repetitive membrane potential (E(m)) depolarization from -90 to 0 mV in rabbit and ferret ventricular myocytes induces a facilitation or 'staircase' of Ca current (I(Ca)), which is Ca (not E(m)) dependent and takes several seconds to accumulate and dissipate. That is, I(Ca) at the tenth pulse at 1- 2 Hz exceeds that at the first pulse (I10 > I1). The I(Ca) staircase was completely abolished by dialysis with either of two inhibitory peptides of Ca-calmodulin-dependent protein kinase (CaMKII) [CaMKII(290-309) and CaMKII(273-302)], implicating this kinase. Inclusion of ATPγS in the patch pipette gradually increased I(Ca) but also abolished the staircase implicating phosphorylation. KN-62, a nonpeptide CaMKII inhibitor, reversed the I(Ca) staircase (I1 > I10). However, this effect of KN-62 was largely attributed to a slower recovery from inactivation and a gating shift to more negative E(m) (not seen with CaMKII peptides). Similar results were obtained with H-89 and staurosporine (inhibitors of adenosine 3',5'-cyclic monophosphate and phospholipid-/Ca-dependent protein kinase, respectively). The reversal of the I(Ca) staircase with H-89 and KN-62 could be prevented by more negative interpulse E(m) or elevation of extracellular [Ca] (which could counteract changes in channel gating due to a reduction in internal negative surface potential). That is, these kinase inhibitors might decrease phosphorylation at the inner membrane surface. In ~30% of the cells studied with H-89 and staurosporine the characteristic kinetic difference in I(Ca) inactivation (faster at I1 than I10) was also diminished. This might be due to a relatively nonspecific inhibition of the same protein kinase inhibited by the CaMKII peptides. We conclude that the Ca-dependent I(Ca) facilitation is due to activation of CaMKII and phosphorylation of a site on or near the Ca channel. KN-62, H-89, and staurosporine shifted I(Ca) gating to more negative potentials and slowed recovery from inactivation, effects that could be due to reduction in phosphorylation at the inner membrane surface. Thus the reversal of the I(Ca) staircase by KN-62, H-89, and staurosporine may not be Ca channel specific.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Issue number3 36-3
StatePublished - 1994
Externally publishedYes


  • calcium-calmodulin- dependent protein kinase
  • cardiac myocyte
  • H-89
  • KN-62
  • staircase
  • staurosporine

ASJC Scopus subject areas

  • Physiology
  • Agricultural and Biological Sciences(all)


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