Calmodulin stimulates adenylate cyclase activity and increases dopamine activation in bovine retina

Abstract

Adenylate cyclase activity in bovine retina is highly responsive to Ca2+ and the endogenous Ca2+-binding protein, calmodulin (CaM). CaM stimulated adenylate cyclase activity in washed particulate fractions of bovine retina by 6.6-fold in a Ca2+-dependent manner. Activation of adenylate cyclase activity by CaM was maximal at 0.12 microM free Ca2+. The apparent Ka for calmodulin stimulation of adenylate cyclase was 67 nM and the apparent Vmax was 116 pmol/min/mg of protein above basal activity. Adenylate cyclase activity in bovine retina was stimulated approximately 50% by guanosine 5'-triphosphate (GTP), but the nonhydrolyzable GTP analogue, guanosine-5'-(beta, gamma-imido)triphosphate (Gpp(NH)p), was able to activate the enzyme nearly 5-fold. CaM and Gpp(NH)p appeared to be partially competitive activators of adenylate cyclase in the retina particulate fraction. Dopamine stimulated adenylate cyclase activity in the presence of GTP with an apparent Ka of 1.0 microM and an apparent Vmax of 66 pmol/min/mg of protein. Ca2+ and CaM increased the apparent Vmax of the dopamine-stimulated adenylate cyclase activity more than 2-fold to a level of 146 pmol/min/mg of protein but did not alter the apparent Ka. This suggests that CaM is an endogenous modulator of dopamine-stimulated adenylate cyclase activity in the retina. CaM-stimulated adenylate cyclase activity may be a common component to retina since we found this activity in retinas from rabbit, rat, and goldfish as well as cow.

Sensitivity of the Human Myometrial Adenylate Cyclase to Calcium and Calmodulin

“…In our myometrial membrane prepara tions, low concentrations of Ca2+ were able to stimulate the adenylate cyclase activity in the presence of exoge nous calmodulin. We observed a moderate stimulation as in most other systems [3,10,12], However, when high endogenous calmodulin concentration is present in our membrane fraction, we cannot observe the stimulatory effect of exogenous calmodulin. But in such conditions, it is possible to block the enzymatic activity by calmodu lin inhibitors such as trifluoroperazine and calmidazolium.…”

Intracellular calcium release resulting from mGluR1 receptor activation modulates GABAA currents in wide‐field retinal amacrine cells: a study with caffeine

“…Although Ca 2 / calmodulin is able to modulate ion channels directly (Ehlers et al, 1996;Deschenes et al, 2002), it is also known to regulate the activity of other enzymes. For example, Ca 2 /calmodulin is known to stimulate adenylate cyclase activity in retinal preparations (Gnegy et al, 1984). However, we could not reproduce the caffeine effect on the GABA current by applying 8-Br-cAMP, so the cAMP cascade does not seem to be involved in the caffeine effect in WFACs.…”

“…, 2002), it is also known to regulate the activity of other enzymes. For example, Ca 2+ /calmodulin is known to stimulate adenylate cyclase activity in retinal preparations (Gnegy et al. , 1984).…”

“…On the one hand, if caffeine blocked PDE in WFACs, the intracellular cAMP level should increrase to reduce I GABA . On the other hand, if caffeine released Ca 2 from intracellular stores, it was also possible that the caffeine effect on GABA-mediated currents evolved through a Ca 2 , Ca 2 /calmodulin, adenylate cyclase, cAMP pathway as in other retinal preparations (Gnegy et al, 1984). The cAMP in turn may activate cAMP-dependent protein kinase A, such as in cultured mouse neurons, to modulate GABA A currents (Porter et al, 1990).…”

Dopamine and full‐field illumination activate D1 and D2‐D5‐type receptors in adult rat retinal ganglion cells

“…How retinal ganglion cells utilize D1 and/or D2-D5 receptors will depend on their distribution in structural compartments of single cells (Hersch et al, 1995; Lee et al, 2004), the G-proteins recruited (Neve et al, 2004), whether dopamine activates Ca 2+ -stimulated as well as Ca 2+ -insensitive adenylyl cyclases (Abdel-Majid et al, 2002; Dunn et al, 2009) in individual cells, whether the effects of calmodulin and adenylyl cyclase activation are additive or synergistic (Gnegy et al, 1984; Sano, 1985), the duration and intensity of Ca 2+ rises (Dunn et al, 2006, 2009), and the relative strengths of the signals they drive. For example, the rise in cAMP could be due to activation of adenylyl cyclases by D1a receptors and G s or G olf (Neve et al, 2004), or to activation of adenylyl cyclases by Ca 2+ influx following D2–D5 receptor and G q activation (Hasbi et al, 2010).…”