Role of cAMP‐dependent protein kinase A in activation of a voltage‐sensitive release mechanism for cardiac contraction in guinea‐pig myocytes

Abstract

It is well established that initiation of contraction in cardiac muscle is triggered by a rise in intracellular free Ca¥. Only two sources are believed to contribute significantly to this increase in Ca¥: (1) influx of Ca¥ through the sarcolemma, primarily through voltage-gated L-type Ca¥ channels and sometimes by reverse Na¤-Ca¥ exchange (Na¤-Ca¥ex), and (2) release of internal stores of Ca¥ from the sarcoplasmic reticulum (SR) by way of SR release channels, also known as ryanodine receptors. SR Ca¥ release triggered by depolarization of the sarcolemma can occur via a mechanism described by Fabiato (1985) called Ca¥-induced Ca¥ release (CICR). With this mechanism, a small amount of Ca¥ entering the cell as L-type Ca¥ current (ICa,L) or by way of reverse Na¤-Ca¥ex can bind to an activation site on the SR

Diminished Inotropic Response to Amrinone in Ventricular Myocytes from Myopathic Hamsters Is Linked to Depression of High-Gain Ca2+-Induced Ca2+Release

“…The contribution of high-gain CICR to myocyte contraction is modulated by phosphorylation through the cAMP-dependent protein kinase A (PKA) and Ca 2ϩ calmodulin kinase pathways (Hobai et al, 1997;Ferrier et al, 1998;Zhu and Ferrier, 2000;Ferrier and Howlett, 2003). Modulation of high-gain CICR by PKA appears to be highly compartmentalized.…”

Protein Kinase A-Mediated Phosphorylation Contributes to Enhanced Contraction Observed in Mice That Overexpress β-Adrenergic Receptor Kinase-1

“…Previous studies have shown that dialysis with pipette solutions can disrupt the adenylyl cyclase-protein kinase A pathway and alter contractile function and that inclusion of cAMP in pipette solutions can restore contractile function in ventricular myocytes (Ferrier et al, 1998;. Therefore, we next determined whether inclusion of cAMP in patch pipette solutions would restore the differences in contraction observed in undialyzed cells between wild-type and ␤ARK-1 myocytes.…”

“…We hypothesized that enhanced protein kinase A-mediated phosphorylation might account for differences in contraction between wild-type and ␤ARK-1 myocytes. Indeed, the selective protein kinase A inhibitor H89 (Bassani et al, 1995;Ferrier et al, 1998) abolished the difference in cell shortening between ␤ARK-1 and wild-type myocytes when cells were dialyzed with 8-bromo-cAMP. These results suggest that enhanced protein kinase A-mediated phosphorylation of components important in cardiac EC-coupling can explain the increase in cell shortening in ␤ARK-1 myocytes dialyzed with 8-bromo-cAMP.…”

“…This suggests that a component required to increase the extent of cell shortening in ␤ARK-1 myocytes was removed from the cells by dialysis. Because dialysis with pipette solutions can disrupt the cAMP-protein kinase A pathway and affect contractile function in ventricular myocytes (Ferrier et al, 1998;, we hypothesized that removal of signaling components important in this pathway might reduce the extent of cell shortening in ␤ARK-1 cells. Therefore, myocytes were dialyzed with pipette solutions supplemented with phosphodiesterase-resistant 8-bromocAMP.…”

“…Therefore, we next determined whether enhanced protein kinase A-mediated phosphorylation might contribute to differences between wild-type and ␤ARK-1 myocytes. In these experiments, cells were dialyzed with 8-bromo-cAMP and superfused with buffer in the absence and presence of the protein kinase A inhibitor H89 (Bassani et al, 1995;Ferrier et al, 1998). The experimental protocol involved a test step from Ϫ40 to 0 mV delivered after a train of conditioning pulses as shown at the top of Fig.…”