cGMP-mediated Ca2+ release from IP3-insensitive Ca2+ stores in smooth muscle

Area of Science:

• Gastroenterology
• Cellular Physiology
• Molecular Pharmacology

Background:

• Nitric oxide (NO) signaling in gastrointestinal smooth muscle involves cyclic guanosine monophosphate (cGMP).
• Previous research suggested cGMP might act as a calcium-mobilizing messenger independently of protein kinase G (PKG).

Purpose of the Study:

• To investigate the role of cGMP as a calcium-mobilizing messenger in gastric smooth muscle cells.
• To determine if cGMP can induce calcium release in the absence of PKG activity.

Main Methods:

• Dispersed gastric smooth muscle cells were used.
• Cells were treated with 8-bromo-cGMP (8-BrcGMP), nitric oxide (NO), and vasoactive intestinal peptide (VIP).
• Inhibitors of cAMP-dependent protein kinase (PKA) and PKG (H-89, KT-5823) were employed, along with thapsigargin to deplete calcium stores.

Main Results:

• 8-BrcGMP, NO, and VIP stimulated 45Ca2+ release in the presence of PKA and PKG inhibitors.
• cGMP-induced calcium release was concentration-dependent.
• cGMP and NO increased cytosolic free calcium concentration ([Ca2+]i) and induced muscle contraction, effects abolished by thapsigargin.
• cGMP-induced calcium release was additive to inositol 1,4,5-trisphosphate (IP3)-induced release and originated from an IP3-insensitive store.

Conclusions:

• In the absence of PKA and PKG activity, cGMP acts as a calcium-mobilizing messenger in gastric smooth muscle.
• cGMP stimulates calcium release from an IP3-insensitive intracellular store.
• The calcium release mechanism is additive to IP3-mediated calcium release.