Endocrine Abstracts

It is generally accepted that hepatic responses to α-adrenergic agonists are dependent on the redistribution of intracellular and also extracellular Ca²⁺. Besides, phenylephrine induces significant ^K+ flux changes and plasma membrane hyperpolarisation. Earlier it was shown that ^K+ channel blockers as well as chelating of extracellular Ca²⁺ with EGTA could inhibit phenylephrine-induced metabolic responses and activation of mitochondrial processes. Taking into account the significance and interplay of Ca²⁺ and ^K+ ions in α-adrenergic regulation of liver metabolism and mitochondrial responses we have investigated phenylephrine-induced ΔΨm changes in single hepatocytes at different conditions of Ca²⁺ or ^K+ fluxes.

Quantitative microfluorimetry with using mitochondrial probe JC-1 allowed evaluating the ΔΨm changes in single hepatocytes. The fluorescence of J-aggregates at 590 nm gives an index of ΔΨm.

It was shown that ΔΨm increased within 15 min of the phenylephrine action on hepatocytes (140±7% relative to control) and fell gradually to 104±6% during 30 min experiment. ^K+ channel blockers – Ba²⁺(2 mM) and 4-aminopyridine (5 mM) decreased the mitochondrial response. ΔΨm was 115±8% and 102±9% in the presence of Ba²⁺ and 4-AP, respectively (15 min). ΔΨm progressively fell down below the control values (up to 75% in both cases at 30 min). But 0.1 mM Ba ²⁺ did not change the agonist-simulated ΔΨm response (147±14% and 112±10% 15 and 30 min, respectively). Plasma membrane depolarization with elevated extracellular ^K+(140 mM) turned effect of phenylephrine to opposite and decreased ΔΨm below control values (49±8% within 15 min). 1 mM EGTA influenced on phenylephrine-induced ΔΨm changes in the same way as extracellular high ^K+(49±9%).

The data obtained suggest that complete or partial plasma membrane depolarization due to alterations of ^K+ fluxes causes changes in transmission of α-adrenergic agonists signal to mitochondrial compartments.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.