Increased secretory capacity of mouse adrenal chromaffin cells by chronic intermittent hypoxia: involvement of protein kinase C

Abstract

Previous studies have shown that catecholamine secretion from the adrenal medulla plays a critical role in chronic intermittent hypoxia (CIH)-induced alterations in cardiovascular function. In the present study we examined the cellular mechanisms associated with the effects of CIH on adrenal chromaffin cell catecholamine secretion. Experiments were performed on adult male mice (C57/BL6) that were exposed to 1-4 days of CIH or to normoxia. Perforated patch electrical capacitance recordings were performed on freshly prepared adrenal medullary slices that permit separating the chromaffin cell secretion from sympathetic input. CIH resulted in a significant increase in the readily releasable pool (RRP) of secretory granules, and decreased stimulus-evoked Ca 2+ influx. Continuous hypoxia (CH) either for 2.5 h (equivalent to hypoxic duration accumulated over 4 days of CIH) or for 4 days were ineffective in evoking changes in the RRP and Ca 2+ influx. CIH activated PKC in adrenal medullae as evidenced by increased phosphorylation of PKC at Thr 514 and PKC inhibitors prevented CIH-induced increases in the RRP and restored stimulus-evoked attenuation of Ca 2+ influx. CIH resulted in elevated thio-barbituric acid reactive substances (TBARSs, an index of oxidized proteins) and an antioxidant prevented CIH-induced changes in the RRP, suggesting the involvement of reactive oxygen species (ROS). These results demonstrate that CIH increases the RRP in adrenal chromaffin cells via ROS-mediated activation of PKC and suggest that CIH can directly affect the secretory capacity of chromaffin cells and contribute, in part, to elevated catecholamine levels.

RETRACTED: Mutual antagonism between hypoxia-inducible factors 1α and 2α regulates oxygen sensing and cardio-respiratory homeostasis

“…Simulating recurrent apnea by exposing rodents to intermittent hypoxia produces an imbalance in HIF-α isoforms manifested by increased HIF-1α (30) and decreased HIF-2α (18) protein levels in the CB and AM. Intermittent hypoxia-exposed rodents exhibit oxidative stress, increased Nox2 and decreased Sod2 levels, augmented hypoxic responses by the CB and AM, hypertension, and breathing abnormalities (30)(31)(32), which recapitulate the phenotype of Hif-2α +/− mice. Remarkably, either blockade of changes in HIF-α isoforms or normalization of the intracellular redox state by antioxidants reverses the effects of intermittent hypoxia in rodents (18,(29)(30)(31)(32)(33).…”

“…Intermittent hypoxia-exposed rodents exhibit oxidative stress, increased Nox2 and decreased Sod2 levels, augmented hypoxic responses by the CB and AM, hypertension, and breathing abnormalities (30)(31)(32), which recapitulate the phenotype of Hif-2α +/− mice. Remarkably, either blockade of changes in HIF-α isoforms or normalization of the intracellular redox state by antioxidants reverses the effects of intermittent hypoxia in rodents (18,(29)(30)(31)(32)(33). Thus, correcting the changes in intracellular redox state by selective modulation of either HIF-1α or HIF-2α expression may represent a unique therapeutic approach for the treatment of cardio-respiratory abnormalities caused by sleep disordered breathing with apnea.…”

Recent Insights on Circulating Catecholamines in Hypertension

“…Alternatively, chronic intermittent hypoxia attenuates baroreflex function, which might abrogate the normal inhibition of sympathetic activity by arterial baroreflex [20]. Hypoxia in animal models also directly affects chromaffin cells of the adrenal medulla, promoting increased secretion of catecholamines [21] as well as stimulating the expression of enzymes for catecholamine synthesis such as tyrosine hydroxylase, dopamine beta hydroxylase, and phenylethanolamine-N-methyltransferase [22,23] (Fig. 1).…”

Reduced calcium current density in female versus male mouse adrenal chromaffin cells in situ

“…Still other work has shown that PKC activation can occur in a Ca 2+ -mediated manner in response to repetitive cell stimulation [20]. Subsequent reports have shown that the PKC-sensitive step in RRP augmentation is likely the phosphorylation of the SNARE protein SNAP-25 [38], and that PKC-mediated augmentation is a key component of increased adrenal output under native hypoxic stress in whole animals [3, 39]. Lastly, in a parallel signaling path, adrenal chromaffin cells have been shown to be highly sensitive to splanchnic release of the potent peptide secretagogue, PACAP [33, 40, 41].…”