Forty years of the adrenal chromaffin cell through ISCCB meetings around the world

Abstract

This historical review focuses on the evolution of the knowledge accumulated during the last two centuries on the biology of the adrenal medulla gland and its chromaffin cells (CCs). The review emerged in the context of a series of meetings that started on the Spanish island of Ibiza in 1982 with the name of the International Symposium on Chromaffin Cell Biology (ISCCB). Hence, the review is divided into two periods namely, before 1982 and from this year to 2022, when the 21st ISCCB meeting was just held in Hamburg, Germany. The first historical period extends back to 1852 when Albert Kölliker first described the fine structure and function of the adrenal medulla. Subsequently, the adrenal staining with chromate salts identified the CCs; this was followed by the establishment of the embryological origin of the adrenal medulla, and the identification of adrenaline-storing vesicles. By the end of the nineteenth century, the basic morphology, histochemistry, and embryology of the adrenal gland were known. The twentieth century began with breakthrough findings namely, the experiment of Elliott suggesting that adrenaline was the sympathetic neurotransmitter, the isolation of pure adrenaline, and the deciphering of its molecular structure and chemical synthesis in the laboratory. In the 1950s, Blaschko isolated the catecholamine-storing vesicles from adrenal medullary extracts. This switched the interest in CCs as models of sympathetic neurons with an explosion of studies concerning their functions, i.e., uptake of catecholamines by chromaffin vesicles through a specific coupled transport system; the identification of several vesicle components in addition to catecholamines including chromogranins, ATP, opioids, and other neuropeptides; the calcium-dependence of the release of catecholamines; the underlying mechanism of exocytosis of this release, as indicated by the co-release of proteins; the cross-talk between the adrenal cortex and the medulla; and the emission of neurite-like processes by CCs in culture, among other numerous findings. The 1980s began with the introduction of new high-resolution techniques such as patch-clamp, calcium probes, marine toxins-targeting ion channels and receptors, confocal microscopy, or amperometry. In this frame of technological advances at the Ibiza ISCCB meeting in 1982, 11 senior researchers in the field predicted a notable increase in our knowledge in the field of CCs and the adrenal medulla; this cumulative knowledge that occurred in the last 40 years of history of the CC is succinctly described in the second part of this historical review. It deals with cell excitability, ion channel currents, the exocytotic fusion pore, the handling of calcium ions by CCs, the kinetics of exocytosis and endocytosis, the exocytotic machinery, and the life cycle of secretory vesicles. These concepts together with studies on the dynamics of membrane fusion with super-resolution imaging techniques at the single-protein level were extensively reviewed by top scientists in the field at the 21st ISCCB meeting in Hamburg in the summer of 2022; this frontier topic is also briefly reviewed here. Many of the concepts arising from those studies contributed to our present understanding of synaptic transmission. This has been studied in physiological or pathophysiological conditions, in CCs from animal disease models. In conclusion, the lessons we have learned from CC biology as a peripheral model for brain and brain disease pertain more than ever to cutting-edge research in neurobiology. In the 22nd ISCCB meeting in Israel in 2024 that Uri Asheri is organizing, we will have the opportunity of seeing the progress of the questions posed in Ibiza, and on other questions that undoubtedly will arise.

The Role of Nicotinic Receptors on Ca2+ Signaling in Bovine Chromaffin Cells

“…The calcium current passing through nicotinic receptors is, in fact, a very small part of the total calcium current (about 2.5%) needed for exocytosis [23], but it seems to be crucial for two reasons: to load vesicles into the active zones of secretion [6], and to directly improve exocytosis, since receptors appear close to the active zones, too [12]. The study of this calcium-regulated process and the spatial coordination of calcium mechanisms is of high importance since the fusion of chromaffin granules contributes to the understanding of neurosecretion [7,18]. Thus, in this work, we were interested in analyzing the contribution of nicotinic receptors to the calcium signals leading to exocytosis in chromaffin cells.…”

“…Due to its importance, a large amount of experimental work has focused on the study of the different subtypes of calcium channels and their function in the secretory response of chromaffin cells; see reviews [1,18,19] and the references contained therein. In our computational model, we assume that the VDCC cluster is made of two P/Q-type and one L-type calcium channels, following the reported relative densities for bovine chromaffin cells [1,18], the major contribution of non-L channels to exocytosis [18,19], and taking into account data showing that clusters of these specific channel types are located close to SNARE microdomains [17]. Besides the calcium channels, we also included models for the vesicles and secretory machinery, as well as the nicotinic receptors.…”

“…The height of the cylinder is divided into slices of 30 nm to quantify the calcium concentrations over time in these regions. In our model, we consider that the cluster of VDCCs is formed by two P/Q-and one L-type calcium channel, in light of the experimental findings concerning the involvement of high-voltage-activated calcium channels in the exocytotic response of bovine chromaffin cells [1,18,19]. Both P/Q-and L-type calcium channel subtypes were modeled as threestate Markov processes, each characterized by distinct transition rates tailored to match their specific current-to-voltage profiles.…”

The Adrenal Gland of Squamata (Reptilia): A Comparative Overview

“…However, in birds and in some reptiles, just below the connective capsule, the cords of steroidogenic cells assume a ring or basket arrangement at the periphery of the gland, and parallel more deeply, suggesting a functional zonation, that has been observed in birds [8,46,47] and reptiles, in which the existence of several sub-populations of adrenocortical cells is supposed [8,48]. In mammals, the adrenal cortex is organized in an outer However, the chromaffin cells can also be studied with many other histological, histochemical and immunocytochemical methods [43,44]; for example, the NE cells can be identified through the immunopositivity to the enzyme, tyrosine hydroxylase (TH), converting L-tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA) (Figure 2), and by staining with Harris hematoxylin after treatment with citrate buffer at pH 6 [36]. The E cells possess the enzyme PNMT, converting NE into E, and therefore can be identified through the immunopositivity to this enzyme.…”

“…A study, performed in E-deficient mice, generated by knocking out PNMT gene, has recently shown that the E granules still retain their shape and general appearance, despite the lack of E [42]. However, the chromaffin cells can also be studied with many other histological, histochemical and immunocytochemical methods [43,44]; for example, the NE cells can be identified through the immunopositivity to the enzyme, tyrosine hydroxylase (TH), converting L-tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA) (Figure 2), and by staining with Harris hematoxylin after treatment with citrate buffer at pH 6 [36]. The E cells possess the enzyme PNMT, converting NE into E, and therefore can be identified through the immunopositivity to this enzyme.…”