cGMP-mediated Ca 2+ release from IP 3 -insensitive Ca 2+ stores in smooth muscle

• Published in: American Journal of Physiology: Cell Physiology 1998-05, Vol.274 (5), p.C1199-C1205
• Main Authors: Murthy, Karnam S, Makhlouf, Gabriel M
• Format: Article
• Language: English
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.1998.274.5.C1199

Recent studies on the role of nitric oxide (NO) in gastrointestinal smooth muscle have raised the possibility that NO-stimulated cGMP could, in the absence of cGMP-dependent protein kinase (PKG) activity, act as a Ca -mobilizing messenger [K. S. Murthy, K.-M. Zhang, J.-G. Jin, J. T. Grider, and G. M. Makhlouf. Am. J. Physiol. 265 ( Gastrointest. Liver Physiol. 28): G660-G671, 1993]. This notion was examined in dispersed gastric smooth muscle cells with 8-bromo-cGMP (8-BrcGMP) and with NO and vasoactive intestinal peptide (VIP), which stimulate endogenous cGMP. In muscle cells treated with cAMP-dependent protein kinase (PKA) and PKG inhibitors (H-89 and KT-5823), 8-BrcGMP (10 μM), NO (1 μM), and VIP (1 μM) stimulated Ca release (21 ± 3 to 30 ± 1% decrease in Ca cell content); Ca release stimulated by 8-BrcGMP was concentration dependent with an EC of 0.4 ± 0.1 μM and a threshold of 10 nM. 8-BrcGMP and NO increased cytosolic free Ca concentration ([Ca ] ) and induced contraction; both responses were abolished after Ca stores were depleted with thapsigargin. With VIP, which normally increases [Ca ] by stimulating Ca influx, treatment with PKA and PKG inhibitors caused a further increase in [Ca ] that reverted to control levels in cells pretreated with thapsigargin. Neither Ca release nor contraction induced by cGMP and NO in permeabilized muscle cells was affected by heparin or ruthenium red. Ca release induced by maximally effective concentrations of cGMP and inositol 1,4,5-trisphosphate (IP ) was additive, independent of which agent was applied first. We conclude that, in the absence of PKA and PKG activity, cGMP stimulates Ca release from an IP -insensitive store and that its effect is additive to that of IP .