Tyrosine Phosphatase Inhibitors Selectively Antagonize β-Adrenergic Receptor-Dependent Regulation of Cardiac Ion Channels

Abstract

␤-Adrenergic receptor stimulation regulates the activity of several different cardiac ion channels through an adenylate cyclase/cAMP/protein kinase A-dependent mechanism. Previous work has suggested that basal tyrosine kinase activity attenuates the ␤-adrenergic responsiveness of these cardiac ion channels, supporting the idea that tyrosine phosphorylation exerts an inhibitory effect at some point in the common signaling pathway. To determine which element in the ␤-adrenergic pathway is regulated by tyrosine kinase activity, we studied the effects of various protein tyrosine phosphatase (PTP) inhibitors on the cAMP-dependent regulation of the L-type Ca 2ϩ current in guinea pig ventricular myocytes. Three such compounds, sodium orthovanadate, peroxovanadate, and bpV(phen), had no effect on the basal Ca 2ϩ current, yet each caused a pronounced inhibition of the Ca 2ϩ current stimulated by the ␤-adrenergic receptor agonist isoproterenol. These observations are consistent with the idea that basal tyrosine kinase activity is capable of inhibiting ␤-adrenergic responses. However, these PTP inhibitors had no effect on cAMP-dependent stimulation of the Ca 2ϩ current via activation of adenylate cyclase with forskolin or activation of H 2 -histaminergic receptors with histamine. These results are consistent with the idea that inhibition of PTP activity produces an inhibitory effect involving a tyrosine kinase-dependent mechanism acting selectively at the level of the ␤-adrenergic receptor. This signaling mechanism does not seem to be linked to tyrosine kinase activity associated with insulin and insulin-like growth factor receptors, because acute exposure to agonists of these receptors did not inhibit isoproterenol regulation of the Ca 2ϩ current.

Redox modulation of basal and β‐adrenergically stimulated cardiac L‐type Ca2+ channel activity by phenylarsine oxide

“…We previously demonstrated that genistein, a tyrosine kinase inhibitor, can increase the sensitivity of cardiac ion channels to b 1 -AR stimulation, suggesting that basal tyrosine kinase activity inhibits badrenergic responsiveness in cardiac myocytes (Hool et al, 1998). Consistent with this idea, we found that vanadate derivatives that inhibit tyrosine phosphatase activity can also inhibit b-adrenergic responses, including b-adrenergic stimulation of the L-type Ca 2 þ current (I Ca-L ) (Sims et al, 2000;Belevych et al, 2001). Vanadate can act as a phosphate analog, binding to and inhibiting phosphoryl transfer enzymes like tyrosine phosphatases (Shaver et al, 1995).…”

“…Previous studies have demonstrated that the inhibition of tyrosine phosphatase activity by vanadate derivatives has little or no effect on the basal L-type Ca 2 þ current in cardiac myocytes (Wang & Lipsius, 1998;Ogura et al, 1999;Sims et al, 2000;Belevych et al, 2001). On the other hand, inhibition of tyrosine phosphatase activity by PAO, an arsenicbased compound, has been reported to regulate the basal L-type Ca 2 þ channel activity in vascular smooth muscle cells and neurons (Pafford et al, 1995;Wijetunge et al, 1998).…”

“…We previously demonstrated that the response of the L-type Ca 2 þ current to b-adrenergic stimulation is inhibited by a tyrosine kinase-dependent mechanism acting selectively at the level of the b-AR (Sims et al, 2000;Belevych et al, 2001). This is supported by the observation that vanadate compounds inhibited the L-type Ca 2 þ current stimulated by Iso, but not the basal current or the current stimulated by forskolin (Sims et al, 2000). This suggests that inhibition of tyrosine phosphatase activity affects b-ARdependent responses by blocking cAMP production.…”

Soy-Derived Isoflavones Exert Opposing Actions on Guinea Pig Ventricular Myocytes

“…Myocytes were superfused with 1 M bpV(phen) for 5 min before the effects of 40 M genistein or equol in the continuing presence of 1 M bpV(phen) were determined. One hundred micromolar bpV(phen) has been reported to have no significant effect on I Ca,L in guinea pig ventricular myocytes (Sims et al, 2000), although we found that this concentration of bpV(phen) markedly decreased cell shortening. We therefore chose to use a concentration of 1 M bpV(phen), which has been shown to be effective in inhibiting PTP in cultured hepatoma cells (Posner et al, 1994).…”

Different action of IBMX, isoproterenol and rutin on orthovanadate-induced nitric oxide release in mouse macrophage cells

“…Several effects of isoproterenol on β-adrenergic receptor bearing cells have been antagonised by sodium orthovanadate mainly due to its proteintyrosine phosphatase inhibitory properties (Hudgins and Bond, 1979;Nieder et al, 1979;Churchill and Churchill, 1982;D'Ocon, 1989;Gordon, 1991;Sims et al, 2000). Due to the insulin-like effects of VO 4 , it can antagonise the effects of ISO on lipolysis (Mooney et al, 1989;Li et al, 1997;Castan et al, 1999) as well.…”