Acute and chronic temperature dependence of Na+/H+ exchange activity of Pimephales promelas gills

Comp Biochem Physiol A Mol Integr Physiol. 2021 Jul:257:110975. doi: 10.1016/j.cbpa.2021.110975. Epub 2021 May 8.

Abstract

Na+/H+ exchangers (NHE) mediate at least part of Na+ entry into gill epithelia via Na+/NH4+ exchange. For homeostasis, Na+ entry into and exit via Na+/K+ ATPase from gill epithelia must balance. Na+/K+ ATPase activity is reduced in cold- compared to warm-acclimated freshwater temperate fish. We hypothesized gill NHE activity is greater in warm- than cold-acclimated fish when measured at acclimation temperatures, and NHE activity displays a temperature dependence similar to Na+/K+ ATPase. Since NHE mRNA expression does not differ, we measured the Na+-dependence of pH-induced Na+ fluxes in gill vesicles from warm- and cold-acclimated fathead minnows at 20o and 7 °C, and calculated maximum transport rates (Vmax) and Na+ K1/2s. We also measured NH4+-induced Na+ fluxes and Na+-induced H+ fluxes. In vesicles from warm-acclimated fish, NHE Vmaxs were 278 ± 33 and 149 ± 23 arbitrary unit/s (au/s) and Na+ K1/2s were 12 ± 4 and 6 ± 4 mmol/l when assayed at 20o and 7 °C (p < 0.004), respectively. In vesicles from cold-acclimated fish, Vmaxs were 288 ± 35 and 141 ± 13 au/s and Na+ K1/2s 17 ± 5 and 7 ± 2 mmol/l when assayed at 20o and 7 °C (p < 0.002), respectively. Na+-induced H+ fluxes were 98 ± 8 and 104 ± 26 au/s in warm- and cold-acclimated fish assayed at 20 °C, respectively. Na+/NH4+ exchange was 120 ± 11 and 158 ± 13 au/s in warm- and cold-acclimated fish, respectively. Conclusions: Gill NHE activity was greater in warm- than cold-acclimated fish assayed at acclimation temperatures. The temperature dependence of NHE activity was similar in both groups, but differed from that reported for Na+/K+ ATPase suggesting complex mechanisms to maintain Na+ homeostasis.

Keywords: Ammonium; Na absorption; Na transport; Teleost.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acclimatization / physiology*
  • Ammonium Compounds / chemistry
  • Animals
  • Cold Temperature
  • Cyprinidae / metabolism
  • Cyprinidae / physiology*
  • Fresh Water
  • Gills / physiology*
  • Homeostasis
  • Kinetics
  • Osmolar Concentration
  • Potassium / chemistry
  • RNA, Messenger / metabolism
  • Sodium / chemistry
  • Sodium-Potassium-Exchanging ATPase / metabolism*
  • Temperature

Substances

  • Ammonium Compounds
  • RNA, Messenger
  • Sodium
  • Sodium-Potassium-Exchanging ATPase
  • Potassium