Ca2+ is universal secondary messenger within eukaryotic cells, triggering multiple cascades of physiological processes in response to the primary effector proteins (Luan and Wang, 2021) such as metabolism control, motor activity of the cytoskeleton, exocytosis of molecules, gene transcription, apoptosis, and others (Ikura et al., 2002; Annunziato et al., 2003; Brini et al., 2014; Lai et al., 2017; Denesyuk et al., 2017; Samanta et al., 2018). These actions of calcium ions are realized by the so-called calcium-binding proteins (Baimbridge et al., 1992), which are a wide group of homologous proteins with a specific molecular structure that capture Ca2+ (Andressen et al., 1993). The history of the study of calcium-binding proteins dates back to the discovery of parvalbumin (PV) protein within the muscles of lower vertebrates by Deuticke in 1934 (Yáñez et al., 2012). Forty years after that discovery, both the amino acid sequence and three-dimensional structure of PV were presented by Nockolds and colleagues (Nockolds et al., 1972). Parvalbumin comes from the Latin word parvus (which means small), which reflects the small molecular weight of this protein and its albumin-like solubility (Blum et al., 1977; Schwaller, 2009). Later, two isoforms of PV, so-called α and β (also called oncomodulin because it was first detected in cancer cells), were identified. They are significantly different in structure, their affinity to Ca2+, cellular expression, and chromosomal localization of the gene (Föhr et al., 1993). In this review, we will discuss only α-parvalbumin, hereafter referred to as simply parvalbumin.

PV has a molecular weight of approximately 12 kDa and consists of three classical EF-hand domains, only two (the second and third) of which provide binding of Ca2+ (with high affinity) and Mg2+ (with moderate affinity) (Reid and Hodges, 1980; Ulfig, 2002). The first EF-hand domain does not bind Ca2+ because it is covered with a hydrophobic shell formed by the other PV domains (Kawasaki and Kretsinger, 2017). In the vertebrate genome, PV is coded by the gene Pvalb (The UniProt Consortium, 2023), and it is a representative of the PARV subfamily of EF-hand proteins (Kawasaki and Kretsinger, 2017). PV is a slow buffering cytosolic protein with a high rate of intracellular mobility (Schwaller, 2009); therefore, it is represented not only in the soma but also within the dendrites and axons (Heizmann, 1984). Because Ca2+ capturing by PV is associated with the need to open active sites of EF-hand domains during the destruction of their bond with Mg2+, PV acts as a low-rate Ca2+ buffer (Schwaller, 2009). High levels of PV have a protective role in Ca2+ overload for both brain and spinal neurons (Nitsch et al., 1989; Heizmann and Braun, 1992; Van Den Bosch et al., 2002).

PV is a marker for the fast-spiking inhibitory interneurons in both the brain (Celio, 1986; Caillard et al., 2000; Amadeo et al., 2001) and spinal cord (Antal et al., 1991; Laing et al., 1994). However, both inhibitory and excitatory populations have been documented in some structures of the nervous system (Gradwell et al., 2022; Abraira et al., 2017). Knowledge of these heterogeneous populations allows extensive progress regarding the structure, function, ontogeny, and pathogenesis of the central nervous system. There are numerous reviews on these aspects of the brain (Baimbridge et al., 1992; Fairless et al., 2019; Kelemen and Szilágyi, 2021; Ruden et al., 2021). However, we did not find a comprehensive review devoted to the features and dynamic of PV expression within the spinal cord. The spinal cord is responsible for multiple vital functions related to the locomotor, postural (Edgerton et al., 2008), and visceral control (Henke et al., 2022) and contains populations of parvalbumin-expressing (PV+) cells (Ren and Ruda, 1994). In this work, we reviewed the comparative distribution and functioning of PV-containing neuronal populations in the spinal cords of mammals.