AMPK-dependent nitric oxide release provides contractile support during hyperosmotic stress

Area of Science:

• Cardiology
• Cell Physiology
• Biochemistry

Background:

• Cardiac cells experience hyperosmotic stress (HS) and shrinkage in pathological states, leading to contractile dysfunction.
• Nitric oxide (NO) is known to modulate cardiac contractility and cell survival.

Purpose of the Study:

• To investigate if HS increases NO production in cardiac cells.
• To determine the impact of HS-induced NO on the negative inotropic effect during hyperosmotic stress.

Main Methods:

• Cardiac myocytes were exposed to hypertonic solutions (440 mOsm) to induce HS.
• NO production was measured using DAF-FM fluorescence.
• Inhibitors of NO synthase (L-NAME, nitroguanidine, Wortmannin), AMPK (Dorsomorphin), guanylate cyclase (ODQ), and PKG (KT5823) were used.
• Western blot analysis assessed nNOS and eNOS phosphorylation.

Main Results:

• HS decreased cardiac myocyte volume and increased NO production.
• HS activated both neuronal nitric oxide synthase (nNOS) and endothelial nitric oxide synthase (eNOS), indicated by increased phosphorylation.
• AMP-activated protein kinase (AMPK) inhibition prevented HS-induced nNOS/eNOS activation and NO production.
• Inhibition of NO signaling pathways (via L-NAME, Dorsomorphin, ODQ, or KT5823) exacerbated the HS-induced negative inotropic effect.

Conclusions:

• HS activates nNOS and eNOS in cardiac myocytes through an AMPK-dependent mechanism, leading to increased NO production.
• NO signaling, via a cGMP/PKG-dependent pathway, provides contractile support during HS.
• This AMPK-dependent NO release mechanism may have pathophysiological relevance in reducing contractile dysfunction under hyperosmotic stress.