The Ca2+ dependence of rat caudate nucleus microsomal adenylate cyclase [ATP pyrophosphate-lyase (cyclizing) EC 126.96.36.199] was determined and compared with that of cortical microsomes. Both cyclase preparations exhibited a biphasic response to Ca2+ with no differences in the free Ca2+ concentrations required to stimulate (one-half maximum = 0.19 μM cortex; 0.2 μM caudate) and inhibit (one-half maximum = 1 μM cortex; 0.9 μM caudate) each cyclase system. Whereas the cortical activity was stimulated 7-fold by Ca2+, the caudate activity exhibited only a 2-fold Ca2+-induced enhancement of basal cyclase. This relative insensitivity of caudate adenylate cyclase is not due to the selective loss of calmodulin. Ca2+ concentrations (0.03-0.5 μM) which stimulate the cyclase and the addition of large excesses of calmodulin had no effect on the ED50 of dopamine. The abilities of Ca2+ and dopamine to stimulate caudate adenylate cyclase activity were additive over the concentration range of 0.03-0.5 μM Ca2+. Ca2+ concentrations (> 0.5 μM) which inhibit adenylate cyclase activity abolished the stimulatory effect of dopamine. Therefore, it is suggested that Ca2+ and dopamine, in a coordinated manner, can modulate the response of caudate adenylate cyclase.
|Original language||English (US)|
|Number of pages||7|
|State||Published - Jan 1 1981|
ASJC Scopus subject areas
- Molecular Medicine