Heterogeneity of Calcium Responses to Secretagogues in Corticotrophs From Male Rats.

Nicola Romanò,Michael J Shipston,Paul Le Tissier,Jamie J Walker,Heather Mcclafferty

doi:10.1210/en.2017-00107

Nicola Romanò, Michael J Shipston + Show 3 more

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https://doi.org/10.1210/en.2017-00107

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Abstract

Heterogeneity in homotypic cellular responses is an important feature of many biological systems, and it has been shown to be prominent in most anterior pituitary hormonal cell types. In this study, we analyze heterogeneity in the responses to hypothalamic secretagogues in the corticotroph cell population of adult male rats. Using the genetically encoded calcium indicator GCaMP6s, we determined the intracellular calcium responses of these cells to corticotropin-releasing hormone and arginine-vasopressin. Our experiments revealed marked population heterogeneity in the response to these peptides, in terms of amplitude and dynamics of the responses, as well as the sensitivity to different concentrations and duration of stimuli. However, repeated stimuli to the same cell produced remarkably consistent responses, indicating that these are deterministic on a cell-by-cell level. We also describe similar heterogeneity in the sensitivity of cells to inhibition by corticosterone. In summary, our results highlight a large degree of heterogeneity in the cellular mechanisms that govern corticotroph responses to their physiological stimuli; this could provide a mechanism to extend the dynamic range of the responses at the population level to allow adaptation to different physiological challenges.

Highlights

In 12 out of 94 cells the response ended before the end of the stimulus; in 13 cells the [intracellular calcium concentration (Ca2+]i) levels started decreasing during the stimulus, but returned to baseline only after its end; in 56 cells the response was sustained during the stimulus, and the response rapidly decreased to baseline levels following the end of the stimulus
We have used changes in corticotroph [Ca2+]i, which have been related to changes in membrane capacitance, indicative of adrenocorticotropic hormone (ACTH) granule fusion and secretion [28], to determine cellular heterogeneity in hypothalamic stimulation and feedback regulation
We report a marked heterogeneity in the responses to secretagogues in rat corticotrophs, which is apparent at multiple levels when analyzing intracellular calcium responses

Summary

Introduction

Our results highlight a large degree of heterogeneity in the cellular mechanisms that govern corticotroph responses to their physiological stimuli; this could provide a mechanism to extend the dynamic range of the responses at the population level to allow adaptation to different physiological challenges. Variability in homotypic cell function is a ubiquitous feature in biology, appearing in a wide range of situations, such as gene expression [1, 2], gene networks [3], molecular pathways [4, 5], and cell behavior [6] This “biological noise” can result from complex nondeterministic molecular dynamics at the microscopic level, and it has been proposed to have an important role in cell and tissue function [7]. CRH and AVP increase the electrical activity of corticotroph cells [13] and increase intracellular calcium concentration ([Ca2+]i) [14]; these two neuropeptides have

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