Phorbol-ester-induced alterations of free calcium ion transients in single rat hepatocytes

Abstract

The effect of the phorbol esters phorbol 12-myristate 13-acetate (TPA) and phorbol 12,13-dibutyrate (PDB) on changes in free Ca2+ concentration ([Ca2+]i) in single rat hepatocytes, microinjected with the photoprotein aequorin, were investigated. [Arg8]vasopressin and phenylephrine induced a series of repetitive [Ca2+]i transients. Phorbol esters inhibited the alpha 1-adrenoceptor-induced response; sub-nanomolar concentrations decreased the transient frequency, and higher concentrations abolished the transients. The inhibitory effect of PDB was readily reversible. Phorbol esters were less effective in decreasing the frequency of [Arg8]-vasopressin-induced transients, and the inhibition could be overcome by high [Arg8]vasopressin concentrations.

Bimodal Acute Effects of A1 Adenosine Receptor Activation on Na+/H+ Exchanger 3 in Opossum Kidney Cells

“…It is interesting that as shown in Figure 3C, co-incubation with the PKC inhibitor calphostin C (10 Ϫ8 M for 15 min) provoked a significant activation of OK-NHE3 activity (by 25.0%; see Figure 3C), whereas cotreatment with TPA (10 Ϫ7 M for 15 min) increased the percentage of inhibition of NHE3 evoked by CPA. Given that the interaction of calphostin C with the regulatory domain of PKC is resistant to the addition of an excess amount of Ca 2ϩ (25) and considering that TPA is able to suppress local Ca 2ϩ oscillations, whereas PKC inhibitors are able to prevent this effect (26,27), the data presented in the Figure 3, B and C, are suggestive for a model in which CPA-induced regulation of NHE3 depends on the combined effect of calcium and PKC. In this model, induction of PKC activity is considered necessary for the inactivation of NHE3, whereas a calcium-sensitive but PKC-independent pathway is critical for upregulation of NHE3 activity.…”

The Metabotropic Glutamate Receptor mGluR5 Induces Calcium Oscillations in Cultured Astrocytes via Protein Kinase C Phosphorylation

“…(Cuthbertson and Cobbold, 1985;Woods et al, 1987;Bird et al, 1993), but target proteins responsible for PKC-mediated [Ca2~] 1 oscillations remained to be identified definitively. Several models for the mechanisms of [Ca 2±j1 oscillations mediated through the IP3/Ca 2~cascade have been proposed, and two basically distinct mechanisms have been discussed and partly supported by experiments: One predicts an oscillating 1P 3 concentration, and another is based on a nonoscillatory 1P3 concentration (Berridge, 1991;Cobbold et al, 1991;Dupont and Goldbeter, 1992).…”

Effect of perturbing diacylglycerol metabolism on cytosolic free Ca2+ oscillations induced in single hepatocytes

“…Iiowever, in hepaiocyies, R 59 022 is mum effective on a molar basis than exogcnously added synthetic DG. Also, free Ca oscillations induced by vasopressin are less sensitive to diCs than those induced by phenylephrine, as has been shown for phorbol esters [9].…”

“…While the frequency of oscillations depends on agonist dose, the time-course of an individual spike does not change with agonist concentration for a giver1 agonist 181. The frequency of spiking is depressed by phorbol ester activation of PMC [9], while inhibitors of PKC prolong the falling phase of each spike [IO]. Here we show the effect on free Ca oscillations of perturbing DG metabolism using a DG-kicase inhibitor, R 59 022, which has been shown to raise DG levels in platelets [ll] and hepatocytes [12], and a DG analogue, diCs.…”

“…Thus we are not yet confident that these data provide convincing support for our Ireceptor controlled model' of the hepatocytc calcium oscillator [18,19], in which transient generation of DG would activate PKC transiently. The reduction of free Ca oscillation frequency by R 59 022 or diC, could be explained by continuous phosphorylation of the hormone receptors by continuous activation of PKC [9,20]. Indeed, PKC inhibitors tend to raise the frequency of the free Ca oscillations when frequency is depressed by phorbol esters [lo].…”