RhoA GTPase regulates L-type Ca²⁺currents in cardiac myocytes

Abstract

Regulation of ionic channels plays a pivotal role in controlling cardiac function. Here we show that the Rho family of small G proteins regulates L-type Ca 2ϩ currents in ventricular cardiomyocytes. Ventricular myocytes isolated from transgenic (TG) mice that overexpress the specific GDP dissociation inhibitor Rho GDI-␣ exhibited significantly decreased basal L-type Ca 2ϩ current density (ϳ40%) compared with myocytes from nontransgenic (NTG) mice. The Ca 2ϩ channel agonist BAY K 8644 and the ␤-adrenergic agonist isoproterenol increased Ca 2ϩ currents in both NTG and TG myocytes to a similar maximal level, and no changes in mRNA or protein levels were observed in the Ca 2ϩ channel ␣1-subunits. These results suggest that the channel activity but not the expression level was altered in TG myocytes. In addition, the densities of inward rectifier and transient outward K ϩ currents were unchanged in TG myocytes. The amplitudes and rates of basal twitches and Ca 2ϩ transients were also similar between the two groups. When the protein was delivered directly into adult ventricular myocytes via TAT-mediated protein transduction, Rho GDI-␣ significantly decreased Ca 2ϩ current density, which supports the idea that the defective Ca 2ϩ channel activity in TG myocytes was a primary effect of the transgene. In addition, expression of a dominant-negative RhoA but not a dominant-negative Rac-1 or Cdc42 also significantly decreased Ca 2ϩ current density, which indicates that inhibition of Ca 2ϩ channel activity by overexpression of Rho GDI-␣ is mediated by inhibition of RhoA. This study points to the L-type Ca 2ϩ channel activity as a novel downstream target of the RhoA signaling pathway.

RhoA GTPase and F-actin Dynamically Regulate the Permeability of Cx43-made Channels in Rat Cardiac Myocytes

“…The data of the present study show that, in rat ventricular myocytes, GJIC strength closely depends on RhoA GTPase activity because activation or inhibition of RhoA activity each result in parallel up-or down-regulations of GJIC; in contrast, the inhibition of the most common RhoA downstream kinase effectors by Y-27632 had no effect. In mouse ventricular myocytes, the inhibition of RhoA (but not Rac1 or Cdc42) decreased the density of L-type calcium currents, whereas Y-27632 had no effect (48).…”

Small G Proteins in the Cardiovascular System: Physiological and Pathological Aspects

“…As there was no change in the levels of mRNA and protein of the L-type Ca 2ϩ channel, this inhibition is due to an effect on the activity of the channel. Expression of a dominant negative form of RhoA but not a dominant negative Rac1 or Cdc42 mimicked the effect of GDI␣ overexpression, indicating that the L-type Ca 2ϩ channel is a downstream target of RhoA in cardiac myocytes (565). The exact molecular mechanism responsible for the positive action of RhoA on the L-type Ca 2ϩ channel has not been precisely defined; however, as the density of channels in the plasma membrane was not modified, it seems to affect the activity of the channel through an actin-independent signal pathway (565).…”

“…Expression of a dominant negative form of RhoA but not a dominant negative Rac1 or Cdc42 mimicked the effect of GDI␣ overexpression, indicating that the L-type Ca 2ϩ channel is a downstream target of RhoA in cardiac myocytes (565). The exact molecular mechanism responsible for the positive action of RhoA on the L-type Ca 2ϩ channel has not been precisely defined; however, as the density of channels in the plasma membrane was not modified, it seems to affect the activity of the channel through an actin-independent signal pathway (565). The progressive atrioventricular conduction defects displayed by GDI␣ overexpressing mice are in agreement with a loss of the positive regulatory role of RhoA on L-type Ca 2ϩ channel activity (522).…”

“…I) RhoA. Ventricular myocytes isolated from transgenic mice carrying a sixfold overexpression of Rho GDI␣ in the myocardium exhibited a 40% decrease in the density of the L-type Ca 2ϩ channel current (565). As there was no change in the levels of mRNA and protein of the L-type Ca 2ϩ channel, this inhibition is due to an effect on the activity of the channel.…”

Rapid Translocation and Insertion of the Epithelial Na+ Channel in Response to RhoA Signaling

“…For example, RhoA and Rac1 have opposing actions on ether a-go-go related gene (ERG) K ϩ channels, with the former rapidly activating the channel and the latter quickly decreasing channel activity (3). RhoA but not closely related Rac1 and Cdc42 modulate I ca in ventricular myocytes (4). H-Ras and Rap1 function as counteracting regulators of voltage-gated sodium current and N-methyl-D-aspartic acid receptor-mediated synaptic transmission (5,6).…”