Salinity-dependent changes in Na+/K+-ATPase content of mitochondria-rich cells contribute to differences in thermal tolerance of Mozambique tilapia

Abstract

The Mozambique tilapia (Oreochromis mossambicus) is prone to osmoregulatory disturbances when faced with fluctuating ambient temperatures. To investigate the underlying causes of this phenomenon, freshwater (FW)- and seawater (SW)-acclimated tilapia were transferred to 15, 25, or 35 degrees C for 2 weeks, and along with typically used indicators of osmoregulatory status [plasma osmolality and branchial and intestinal specific Na(+), K(+)-ATPase (NKA) activity], we used tissue microarrays (TMA) and laser-scanning cytometry (LSC) to characterize the effects of temperature acclimation. Tissue microarrays were stained with fluorescently labeled anti-Na(+), K(+)-ATPase antibodies that allowed for the quantification of NKA abundance per unit area within individual branchial mitochondria-rich cells (MRCs) as well as sections of renal tissue. Mitochondria-rich cell counts and estimates of size were carried out for each treatment by the detection of DASPMI fluorescence. The combined analyses showed that SW fish have larger but fewer MRCs that contain more NKA per unit area. After a 2-week acclimation to 15 degrees C tilapia experienced osmotic imbalances in both FW and SW that were likely due to low NKA activity. SW-acclimated fish compensated for the low activity by increasing MRC size and subsequently the concentration of NKA within MRCs. Although there were no signs of osmotic stress in FW-acclimated tilapia at 25 degrees C, there was an increased NKA capacity that was most likely mediated by a higher MRC count. We conclude on the basis of the different responses to temperature acclimation that salinity-induced changes in the NKA concentration of MRCs alter thermal tolerance limits of tilapia.

Prolonged apoptosis in mitochondria-rich cells of tilapia (Oreochromis mossambicus) exposed to elevated salinity

“…At the same time, this antibody enabled us to quantify NKA abundance in individual MRC and to determine MRC size. While NKA antibodies have previously been used as a MRC marker (Lima and Kültz 2004;Sardella et al 2008) and MRC size has often been measured after live DAPSMI/DASPEI staining (Foskett et al 1981;Kültz et al 1992;Van Der Heijden et al 1997), the Wxation of whole cells on PLL-coated coverslips allowed us to combine these two approaches and utilize NKA antibodies for determination of MRC size in Wxed, dissociated cell populations. This method is advantageous over live cell stains such as DASPMI when co-labeling with dyes that require Wxed cells is desired (for instance TUNEL labeling) and also to measure NKA abundance per MRC.…”

Paracellular pathway remodeling enhances sodium secretion by teleost fish in hypersaline environments

“…Values are means± in SW, the yolk sac membrane, rich in ionocytes and without the shunt formed by lamellae or edge damage, develops a V t of +50±1.7 mV (Guggino, 1980), so this value may be close to the upper limit that these salt-secreting systems can develop. In extremely high salinities of 95‰, Tilapia have elevated plasma Na + to 260 mmol l −1 (Sardella et al, 2008); the calculated E Na of +44.3 mV suggests that fish are forced to adjust their plasma Na + upward, so that the maximal V t can still produce Na + secretion via the paracellular pathway. In contrast, we found that the buccal epithelium, which has few ionocytes, develops much lower V t and I sc , which confirms previous findings (Karnaky, 1980), but we predict that buccal epithelium would not contribute to Na + secretion in SW or 2SW.…”

Short-term effects of thermal stress on the responses of branchial protein quality control and osmoregulation in a reef-associated fish, Chromis viridis

“…Because the previous studies have demonstrated that the specific NKA activity which was measured at the exposed temperature of fish would correlate with the level of in vivo activity (Metz et al 2003;Sardella et al, 2008a), therefore, the reaction was run at the exposure temperatures in this study. The concentration of inorganic phosphate was measured according to Doulgerakia et al (2002).…”

“…Environmental temperature significantly influences internal electrolyte and osmotic homeostasis in aquatic ectotherms (Christensen 1975;Amoudi et al 1996;Metz et al 2003;Sardella et al 2004Sardella et al , 2008a. It is due to active ion-transporting mechanisms that are regulated by many proteins, while the cellular proteins of stenothermal species are only marginally stable at a limited range of temperature (Hochachka and Somero 2002;Metz et al 2003;Crockett and Londraville 2006;Sardella et al 2008a).…”

“…It is due to active ion-transporting mechanisms that are regulated by many proteins, while the cellular proteins of stenothermal species are only marginally stable at a limited range of temperature (Hochachka and Somero 2002;Metz et al 2003;Crockett and Londraville 2006;Sardella et al 2008a). The fundamental transporter proteins responsible for osmoregulation in gill epithelia have been reported in previous studies (see Hirose et al 2003;Evans et al 2005;Hwang and Lee 2007;Kaneko et al 2008;Hwang et al 2011).…”