Cholesterol regulates contractility and inotropic response to β2-adrenoceptor agonist in the mouse atria: Involvement of Gi-protein-Akt-NO-pathway

- We have studied the effects of 1 mM and 5 mM methyl-β-cyclodextrin in the mice atria.
- Cholesterol depletion potentiates both Ca2 + transient and NO production.
- Inotropic response to β2-adrenoceptor agonist is attenuated by cholesterol depletion.
- The last occurs owing to upregulation of Gi-protein-Akt-NO-synthase signaling.
- Main mechanism of the inotropy reduction is dependent on degree of cholesterol loss.

Majority of cardiac β2-adrenoceptors is located in cholesterol-rich microdomains. Here, we have investigated the underlying mechanisms by which a slight to moderate cholesterol depletion with methyl-β-cyclodextrin (MβCD, 1 and 5 mM) interferes with contractility and inotropic effect of β2-adrenergic agonist (fenoterol, 50 μM) in the mouse atria. Treatment with MβCD itself increased amplitude of Ca2 + transient but did not change the contraction amplitude due to a clamping action of elevated NO. Cholesterol depletion significantly attenuated the positive inotropic response to fenoterol which is accompanied by increase in NO generation and decrease in Ca2 + transient. Influence of 1 mM MβCD on the fenoterol-driven changes in both contractility and NO level was strongly attenuated by inhibition of Gi-protein (pertussis toxin), Akt (Akt 1/2 kinase inhibitor) or NO-synthase (L-NAME). After exposure to 5 mM MβCD, pertussis toxin or Akt inhibitor could recover the β2-agonist effects on contractility, NO production and Ca2 + transient, while L-NAME only reduced NO level. An adenylyl cyclase activator (forskolin, 50 nM) had no influence on the MβCD-induced changes in the β2-agonist effects. Obtained results suggest that slight cholesterol depletion upregulates Gi-protein/Akt/NO-synthase signaling that attenuates the positive inotropic response to β2-adrenergic stimulation without altering the Ca2 + transient. Whilst moderate cholesterol depletion additionally could suppress the enhancement of the Ca2 + transient amplitude caused by the β2-adrenergic agonist administration in Gi-protein/Akt-dependent but NO-independent manner.