Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.13.12.5 (aequorin)
 1,451 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Glucagon increases the cytoplasmic free calcium concentration as measured by aequorin bioluminescence. It has been proposed by Wakelam et al. (Nature 323 (1986) 68-71) that low concentrations of glucagon mobilize calcium from an intracellular pool by causing polyphosphoinositide breakdown. To identify whether cyclic AMP mediates changes in the cytoplasmic free calcium concentration ([Ca2+]c) induced by glucagon, the effects of forskolin and exogenous cyclic AMP on [Ca2+]c were compared with that of glucagon in aequorin-loaded hepatocytes. Although the magnitudes of the [Ca2+]c responses to 250 microM forskolin and 1 mM 8-bromo cyclic AMP were identical to that of 5 nM glucagon, these two agents induced a more prolonged elevation of [Ca2+]c. Glucagon-induced elevation of [Ca2+]c was accompanied by a smaller increase in cyclic AMP than that induced by forskolin. When the cyclic AMP response to glucagon was potentiated by an inhibitor of phosphodiesterase, 3-isobutyl-1-methylxanthine, the glucagon-induced increase in [Ca2+]c was not affected. Conversely, when the cyclic AMP response to glucagon was reduced by pretreatment of the cells with angiotensin II, glucagon-induced changes in [Ca2+]c were rather enhanced. Furthermore, vasopressin potentiated glucagon-induced changes in [Ca2+]c despite the reduction of the cyclic AMP response to glucagon. In the presence of 1 microM extracellular calcium, angiotensin II did not enhance glucagon-induced changes in [Ca2+]c. These results suggest that at least part of the action of 5 nM glucagon on calcium mobilization is independent of cyclic AMP.
 ...
PMID:Evidence of cyclic AMP-independent action of glucagon on calcium mobilization in rat hepatocytes. 245 73

Effects of glucagon on cytoplasmic concentration of free calcium, [Ca2+]c, were studied in aequorin-loaded hepatocytes. Addition of 5 nmol/l glucagon resulted in a prompt, but transient increase in aequorin bioluminescence. Glucagon, at 5 nmol/l, induced an increase in [Ca2+]c even in medium containing 1 mumol/l calcium, although the response was considerably smaller than that observed in medium containing 1.0 mmol/l calcium. When hepatocytes incubated in the presence of 1 mumol/l extracellular calcium were first stimulated by phenylephrine and subsequently by either glucagon or angiotensin II, there was a response of [Ca2+]c to glucagon, but not to angiotensin II. Dantrolene (50 mumol/l), which inhibits an increase in [Ca2+]c induced by phenylephrine, did not inhibit the increase in [Ca2+]c induced by glucagon. In contrast, dinitrophenol (50 mumol/l) abolished [Ca2+]c response to glucagon without abolishing the increase in [Ca2+]c induced by angiotensin II. These results suggest that glucagon mobilizes calcium from both intracellular and extracellular pools and that the intracellular calcium pool involved in glucagon action may be different from that mobilized by either phenylephrine or angiotensin II.
 ...
PMID:Sources of calcium mobilized by glucagon in isolated rat hepatocytes. 284 92

Single rat hepatocytes, microinjected with the Ca(2+)-sensitive photoprotein aequorin, respond to agonists acting through the phosphoinositide signalling pathway by the generation of oscillations in cytosolic free Ca2+ concentration ([Ca2+]i). The duration of [Ca2+]i transients generated is characteristic of the receptor species activated; the variability results in differences in the rate of fall of [Ca2+]i from its peak. It is conceivable that the plasma membrane Ca(2+)-ATPase (PM Ca2+ pump) may have an important role in the mechanism underlying agonist specificity. It has recently been shown that an esterified form of carboxyeosin, an inhibitor of the red cell PM Ca2+ pump, is suitable for use in whole cell studies. Glucagon-(19-29) (mini-glucagon) inhibits the Ca2+ pump in liver plasma membranes, mediated by Gs. We show here that carboxyeosin and mini-glucagon inhibit Ca2+ efflux from populations of intact rat hepatocytes. We show that carboxyeosin and mini-glucagon enhance the frequency of oscillations induced by Ca(2+)-mobilizing agonists in single hepatocytes, but do not affect the duration of individual transients. Furthermore, we demonstrate that inhibition of the hepatocyte PM Ca2+ pump enables the continued generation of [Ca2+]i oscillations for a prolonged period following the removal of extracellular Ca2+.
 ...
PMID:Effects on the hepatocyte [Ca2+]i oscillator of inhibition of the plasma membrane Ca2+ pump by carboxyeosin or glucagon-(19-29). 929 28