Extrabranchial mechanisms of systemic pH recovery in hagfish (Eptatretus stoutii).

This study investigates the role of branchial and extrabranchial processes in acid-base regulation in the Pacific Hagfish (Eptatretus stoutii). Hagfish were injected with one of the following solutions: acid saline (250mM HCl [pH=0.60], 250mM NaCl), alkaline saline (250mM NaHCO3, 250mM NaCl, [pH≈8.43]) or control saline (500mM NaCl) in order to achieve an acid/alkaline/saline load of 6000μmol·kg(-1). Using a custom designed hagfish compartmentalizing flux chamber, we partitioned flux of net acid or base equivalents and ammonia into the anterior (gill+skin) and posterior (skin+intestinal/renal/cloacal) components. We found that Pacific hagfish excrete H(+) primarily via branchial mechanisms but base excretion occurs through extrabranchial mechanisms located in the posterior region. In addition, we demonstrate that hagfish are able to excrete ammonia via the skin although this flux was not involved in compensation from an acid-base disturbance.