Sustained oscillations in extracellular calcium concentrations upon hormonal stimulation of perfused rat liver

Abstract

Sustained oscillations in extracellular free Ca2+ were shown to occur on addition of vasopressin, phenylephrine or angiotensin II in isolated rat liver perfused with low (10 microM)-Ca2+ medium. The amplitude and frequency of oscillation depend on hormone concentration. In contrast, Ca2+ releases on addition of ATP, t-butyl hydroperoxide or arachidonate do not exhibit oscillatory behaviour. The vasopressin-induced oscillations were suppressed by glucagon and dibutyryl 3',5'-cyclic AMP, but not by dibutyryl 3',5'-cyclic GMP. These observations in the extracellular space complement observations by Woods, Cuthbertson & Cobbold [(1986) Nature (London) 319, 600-602] on oscillations in intracellular free Ca2+ in single liver cells.

Actions of extracellular UTP and ATP in perfused rat liver

“…In line with a recent report [34] oscillations of the effluent Ca2+ concentrations could not be demonstrated with ATP; however, such a phenomenon could not be excluded in the case of UTP (see Fig. 7).…”

Calcium: its modulation in liver by cross-talk between the actions of glucagon and calcium-mobilizing agonists

“…The amount of Ca2+ released, however, and the rate of release are much less than that mobilized by phenylephrine, vasopressin or angiotensin; these glucagon-induced responses appear to be increased substantially when the extracellular [Ca2+] is lowered (Benedetti et al, 1989 (EGF) (Altin and Bygrave, 1987a) and by phosphatidic acid and arachidonic acid (Altin and Bygrave, 1987b). Preadministration of glucagon to the perfused rat liver was shown to also suppress the oscillations induced by vasopressin alluded to above (Graf et al, 1987). Earlier Jenkinson and Koller (1977) had shown that the combined addition of al-and 8-agonists increased synergistically the efflux of 45Ca from liver slices of the guinea pig.…”

“…As implied above, the two principal experimental systems that have contributed to our current understanding of cellular Ca2+ fluxes in liver are the perfused rat liver and single cells (hepatocytes) prepared therefrom. While each system inherently has particular advantages and disadvantages (see Exton, 1975;Berry et al, 1991) Graf et al (1987).…”

“…and Reinhart et al (1982), Altin and Bygrave (1986) and Benedetti et al (1989). See Graf et al (1987) Reinhart et al, 1984b), the response can be rapidly re-activated by providing an excess of Ca2+ to the perfusate medium.…”

Approches expérimentale et de modélisation de la signalisation calcique dans les cellules

“…Des observations datant de plus de 20 ans, faites dans des expérien-ces réalisées notamment sur des foies entiers perfusés, suggèrent une organisation des signaux calciques dans l'espace et dans le temps au niveau d'un tissu entier [29]. Plus récemment, il a été montré dans certains organes ou dans des systèmes multicellulaires que les vagues calciques intracellulaires observées dans une cellule se propageaient aux cellules adjacentes, que ces dernières soient de même type ou d'un type différent [18].…”