Bicarbonate-sensing soluble adenylyl cyclase is present in the cell cytoplasm and nucleus of multiple shark tissues.

Martin Tresguerres,Jinae N Roa

doi:10.14814/phy2.13090

Abstract

The enzyme soluble adenylyl cyclase (sAC) is directly stimulated by bicarbonate (HCO3 −) to produce the signaling molecule cyclic adenosine monophosphate (cAMP). Because sAC and sAC‐related enzymes are found throughout phyla from cyanobacteria to mammals and they regulate cell physiology in response to internal and external changes in pH, CO2, and HCO3 −, sAC is deemed an evolutionarily conserved acid‐base sensor. Previously, sAC has been reported in dogfish shark and round ray gill cells, where they sense and counteract blood alkalosis by regulating the activity of V‐type H+‐ ATPase. Here, we report the presence of sAC protein in gill, rectal gland, cornea, intestine, white muscle, and heart of leopard shark Triakis semifasciata. Co‐expression of sAC with transmembrane adenylyl cyclases supports the presence of cAMP signaling microdomains. Furthermore, immunohistochemistry on tissue sections, and western blots and cAMP‐activity assays on nucleus‐enriched fractions demonstrate the presence of sAC protein in and around nuclei. These results suggest that sAC modulates multiple physiological processes in shark cells, including nuclear functions.

Highlights

The acid-base status of physiological fluids is largely dictated by pH, CO2, and bicarbonate (HCO3À) levels, and acid-base status is one of the most tightly regulated physiological processes because even small deviations from the acid-base set point can affect the structure and function of enzymes and other cellular components
One evolutionarily conserved acid-base sensing mechanism relies on the enzyme soluble adenylyl cyclase, which is directly regulated by HCO3À to produce the ubiquitous messenger molecule cyclic adenosine monophosphate (Buck et al 1999; Chen et al 2000)
Gill extracts incubated in 40 mmol/L HCO3À produced significantly more cyclic adenosine monophosphate (cAMP) than gill extracts incubated in control conditions (65 Æ 7 pmol lLÀ1 vs. 43 Æ 3 pmol lLÀ1, Fig. 1B); HCO3À-stimulated cAMP production was inhibited by the soluble adenylyl cyclase (sAC)-specific small molecule inhibitor KH7 (Fig. 1B), which is a hallmark of sAC activity

Summary

Introduction

The acid-base status of physiological fluids is largely dictated by pH, CO2, and bicarbonate (HCO3À) levels, and acid-base status is one of the most tightly regulated physiological processes because even small deviations from the acid-base set point can affect the structure and function of enzymes and other cellular components. The acid-base status of extracellular fluids is regulated by specialized organs such as gills, lungs, and kidneys, which provide a stable acid-base environment to the rest of the cells in the body. One evolutionarily conserved acid-base sensing mechanism relies on the enzyme soluble adenylyl cyclase (sAC, adcy10), which is directly regulated by HCO3À to produce the ubiquitous messenger molecule cyclic adenosine monophosphate (cAMP) (Buck et al 1999; Chen et al 2000). SAC has been established as a sensor and regulator of blood acid-base status in the mammalian kidney (Paunescu et al 2008, 2010; Gong et al 2010) and in gills of dogfish shark

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