Plasma Membrane Ca²⁺-ATPase Isoform 2a Is the PMCA of Hair Bundles

Abstract

Mechanoelectrical transduction channels of hair cells allow for the entry of appreciable amounts of Ca2+, which regulates adaptation and triggers the mechanical activity of hair bundles. Most Ca2+that enters transduction channels is extruded by the plasma membrane Ca2+-ATPase (PMCA), a Ca2+pump that is highly concentrated in hair bundles and may be essential for normal hair cell function. Because PMCA isozymes and splice forms are regulated differentially and have distinct biochemical properties, we determined the identity of hair bundle PMCA in frog and rat hair cells. By screening a bullfrog saccular cDNA library, we identified abundant PMCA1b and PMCA2a clones as well as rare PMCA2b and PMCA2c clones. Using immunocytochemistry and immunoprecipitation experiments, we showed in bullfrog sacculus that PMCA1b is the major isozyme of hair cell and supporting cell basolateral membranes and that PMCA2a is the only PMCA present in hair bundles. This complete segregation of PMCA1 and PMCA2 isozymes holds for rat auditory and vestibular hair cells; PMCA2a is the only PMCA isoform in hair bundles of outer hair cells and vestibular hair cells and is the predominant PMCA of hair bundles of inner hair cells. Our data suggest that hair cells control plasma membrane Ca2+-pumping activity by targeting specific PMCA isozymes to distinct subcellular locations. Because PMCA2a is the only Ca2+pump present at appreciable levels in hair bundles, the biochemical properties of this pump must account fully for the physiological features of transmembrane Ca2+pumping in bundles.

Distinct capacity for differentiation to inner ear cell types by progenitor cells of the cochlea and vestibular organs

“…Of phalloidin-positive structures, 50% (27/54) from cochlear progenitors and 73% (58/79) from vestibular progenitors were immunoreactive for plasma membrane Ca 2+ -ATPase 2 (PMCA2; also known as Atp2b2; Fig. 2C,H), which is abundant in postnatal HC bundles (Chen et al, 2012;Dumont et al, 2001;Hill et al, 2006). PMCA2-like immunoreactivity was strong at the base of the actin-positive structures (Fig.…”

Role of nitric oxide on purinergic signalling in the cochlea

“…These results indicate that the ATP-induced Ca 2+ influx via a direct action of P2X receptors may be the source for nNOS activity in the apical region of IHCs and OHCs. It has been shown that the apical region of IHCs and OHCs, including stereocilia and the cuticular plate, is abundant in calmodulin [65], P2X receptors [14], and plasma membrane Ca 2+ -ATPase 2a subunit [66]. Calmodulin binding to nNOS is reported to be essential for the nNOS activity, by which electron transfer is triggered [67].…”

Alternative splice variants of plasma membrane calcium-ATPases in human corneal epithelium

“…For example, PMCA2 and PMCA3 are prevalent in brain (Stauffer et al 1993), but are also found in pancreatic beta cells (Kamagate et al 2000). PMCA2 expression is high in neurosensory hair cells of the inner ear (Dumont et al 2001;Yamoah et al 1998). These PMCA2-containing cells sustain sudden influxes of Ca 2+ upon stimulation that necessitates rapid extrusion to maintain responsiveness .…”