Synergistic interaction between glucagon and calcium-mobilizing agonists in liver

Synergistic interaction between glucagon and calcium-mobilizing agonists in liver 

Blackmore and Exton [5] have provided much evidence that the potentiation by glucagon of the intracellular Ca2+ mobilization induced by vasopressin is due to an enhancement of inositol trisphosphate accumulation (Fig. 11). This is probably true for its synergistic interaction with other Ca2+-mobilizing agonists. All the actions of 

The combination of glucagon with a high concentration of a Ca2+-mobilizing hormone can reverse the loss of Ca2+ from liver cells [159] or lead to a large accumulation of Ca2+ in these cells [160]. This is particularly pronounced when the extracellular Ca2+ concentration is increased [160] (Fig. 12) and presumably reflects a predominance of the stimulation of Ca2+ influx [143-145] over the mobilization of intracellular Ca2+ stores [5] induced by the combined hormones. Analysis of the Ca2+ content of subcellular fractions indicates that the extra Ca2+ accumulated by the cells under these conditions is found principally in the mitochondria [160]. As expected, the cytosolic Ca2+ concentration in the presence of the hormone combination is much greater than seen with either hormone alone (P.F. Blackmore, unpublished observations) and reaches the level ( 600 nM) at which mitochondria begin to accumulate Ca2+. 

Inhibitory action of phorbol esters on glucagon-induced calcium mobilization 

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