DO NITRIC-OXIDE AND CGMP PLAY A ROLE IN CALCIUM CYCLING

The biological molecule NO and its cyclic nucleotide effector molecule cGMP, are involved in a variety of biological systems, This article r eviews evidence supporting a role for these molecules in signal transd uction, Over the last 10 years, it has become evident that these molec ules are important in Ca2+ regulation, particularly in excitable cells . In these cells, cGMP-dependent mechanisms appear to both directly an d indirectly regulate Ca2+ transport, Until recently, reports of the a ctions of cGMP in non-excitable cells have been contradictory, present ing a confusing plethora of effects, In these cells, the cGMP-Ca2+ reg ulation pathway appears to be concentration-dependent, possibly repres enting a negative feedback mechanism, Ca2+ entry appears to be activat ed when low concentrations of cGMP are present, and inhibited at highe r concentrations, The role of cGMP in Ca2+ regulation in non-excitable cells has been largely overlooked and further investigation of this i ssue may provide clues as to the nature of various unknown components that induce Ca2+ entry into these cells.