Expression of α3 and FXYD subunits comprising dynamic sodium pumps in young Xenopus frog tadpoles

Abstract

Animal behaviour relies on output from neuronal networks in the central nervous system (CNS). Evidence has demonstrated that a sub-population of sodium pumps play a dynamic role in modifying network output. Following a period of intense neuronal firing, some sodium pumps are recruited and mediate a minute-long hyperpolarization of the cell membrane known as the ultraslow afterhyperpolarization (usAHP). Previous research has proposed that the usAHP, which is found in only a subset of spinal neurons, is mediated by sodium pumps expressing a subtype of their catalytic α subunit found exclusively in neurons, termed α3. Though α3 is postulated to be heterogeneously expressed in the CNS, until now, there has been no research on the localisation of α3 to neurons in that region. Similarly, no previous research has investigated the distribution of FXYD1, a regulatory subunit in the sodium pump, which is broadly expressed in brain and muscle tissue.

Here, I present the first evidence for α3, FXYD1 and FXYD6 expression within neurons that comprise the rostrocaudal CNS of stage 42 Xenopus laevis larvae, as well as in other tissues, using immunohistochemical labelling techniques I have developed for this project. Furthermore, I outline the potential specific roles for these subunits both throughout locomotor development and their contribution to swimming function by the tadpole larval stage. This was done by developing movement deprivation experiments from embryonic to larval stages in Xenopus using tricaine methanesulfonate (MS-222) and then subsequent fluorescent co-labelling of α3 and FXYD1 with cross-comparison to previous immunolabelling results.