Department of Physiology and Biophysics, Case Western Reserve University, 10900 Euclid Ave, Cleveland, OH 44106, United States of America.
Department of Physiology and Biophysics, Case Western Reserve University, 10900 Euclid Ave, Cleveland, OH 44106, United States of America; Department of Biology, Case Western Reserve University, 2080 Adelbert Road, Cleveland, OH 44106, United States of America.
Comp Biochem Physiol A Mol Integr Physiol. 2021 Jul;257:110975. doi: 10.1016/j.cbpa.2021.110975. Epub 2021 May 8.
Na/H exchangers (NHE) mediate at least part of Na entry into gill epithelia via Na/NH 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 20 and 7 °C, and calculated maximum transport rates (V) and Na Ks. We also measured NH-induced Na fluxes and Na-induced H fluxes. In vesicles from warm-acclimated fish, NHE Vs were 278 ± 33 and 149 ± 23 arbitrary unit/s (au/s) and Na Ks were 12 ± 4 and 6 ± 4 mmol/l when assayed at 20 and 7 °C (p < 0.004), respectively. In vesicles from cold-acclimated fish, Vs were 288 ± 35 and 141 ± 13 au/s and Na Ks 17 ± 5 and 7 ± 2 mmol/l when assayed at 20 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/NH 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.
钠/氢交换器 (NHE) 通过钠/铵交换介导至少部分钠进入鳃上皮细胞。为了维持体内平衡，钠必须通过钠/钾 ATP 酶从鳃上皮细胞进入和离开。与温水适应的淡水温水鱼相比，冷适应的冷水鱼中钠/钾 ATP 酶的活性降低。我们假设在适应温度下测量时，温暖适应的鱼的鳃 NHE 活性高于冷适应的鱼，并且 NHE 活性表现出与钠/钾 ATP 酶相似的温度依赖性。由于 NHE mRNA 表达没有差异，我们测量了在 20 和 7°C 时温暖和冷适应的胖头鲦鳃囊泡中 pH 诱导的钠通量的钠依赖性，并计算了最大转运速率 (V) 和 Na Ks。我们还测量了 NH 诱导的钠通量和 Na 诱导的 H 通量。在温暖适应鱼的囊泡中，NHE Vs 分别为 278±33 和 149±23 个任意单位/秒 (au/s)，Na Ks 分别为 12±4 和 6±4mmol/l，当在 20 和 7°C 下测定时 (p<0.004)。在冷适应鱼的囊泡中，Vs 分别为 288±35 和 141±13 au/s，Na Ks 分别为 17±5 和 7±2mmol/l，当在 20 和 7°C 下测定时 (p<0.002)。在 20°C 下测定时，温暖适应和冷适应鱼的 Na 诱导的 H 通量分别为 98±8 和 104±26 au/s。Na/NH 交换分别为温暖适应和冷适应鱼的 120±11 和 158±13 au/s。结论：在适应温度下测量时，温暖适应的鱼的鳃 NHE 活性高于冷适应的鱼。NHE 活性的温度依赖性在两组中相似，但与报道的钠/钾 ATP 酶不同，表明维持钠体内平衡的机制复杂。
