Rapid desensitization of the nitric oxide receptor, soluble guanylyl cyclase, underlies diversity of cellular cGMP responses

A major receptor for nitric oxide (NO) is the cGMP-synthesizing enzyme, sol uble guanylyl cyclase (sGC), but it is not known how this enzyme behaves in cells. In cerebellar cells, NO (from diethylamine NONOate) increased astro cytic cGMP with a potency (EC50 less than or equal to 20 nM) higher than th at reported for purified sGC. Deactivation of NO-stimulated sGC activity, s tudied by trapping free NO with hemoglobin, took place within seconds (or l ess) rather than the minute time scale reported for the purified enzyme. Me asurement of the rates of accumulation and degradation of cGMP were used to follow the activity of sGC over time. The peak activity, occurring within seconds of adding NO, was swiftly followed by desensitization to a steady-s tate level 8-fold lower. The same desensitizing profile was observed when t he net sGC activity was increased or decreased or when cGMP breakdown was i nhibited. Recovery from desensitization was relatively slow (half-time = 1. 5 min). When the cells were lysed, sGC desensitization was lost. Analysis o f the transient cGMP response to NO in human platelets showed that sGC unde rwent a similar desensitization. The results indicate that, in its natural environment, sGC behaves much more like a neurotransmitter receptor than ha d been expected from previous enzymological studies, and that hitherto unkn own sGC regulatory factors exist. Rapid sGC desensitization, in concert wit h variations in the rate of cGMP breakdown, provides a fundamental mechanis m for shaping cellular cGMP responses and is likely to be important in deco ding NO signals under physiological and pathophysiological conditions.