Physiological response to emersion in the amphibious crab Chasmagnathus granulata Dana (Decapoda Grapsidae): biochemical and ventilatory adaptations

The adaptation of Chasmagnathus granulata to air breathing depends on two t ypes of physiological mechanisms: (1) Biochemical adjustments, comprising t he achievement of new steady state values for partial pressure of carbon di oxide (P-CO2) and total carbon dioxide concentration (C-CO2). The initial i ncrease in hemolymph bicarbonate is stabilized by dehydration to CO2 presum ably catalyzed by carbonic anhydrase (CA) at the basolateral side of the gi ll epithelium. Thus, an adequate transbranchial gradient of P-CO2 is restor ed. Inhibition of CA with acetazolamide (Az) reduces the rate of CO2 excret ion and elevates P-CO2. The respiratory acidosis caused by increased P-CO2 is compensated by increase in the difference between Na+ and Cl- concentrat ions. Az does not affect hemolymph ionic concentrations. (2) Ventilatory: c ontrol: untreated animals show a significant decrease in scaphognathite fre quency (F-SC) during emersion, while Az treated crabs show a slight increas e of this variable. F-SC of Az crabs tends to decrease with hemolymphatic C O2, presumably by clearance of the CA inhibitor from hemolymph. These resul ts suggest that C. granulata possess a ventilatory control based on a prima ry oxygen-dependent stimulus and a secondary one dependent on CO2. (C) 1998 Elsevier Science Inc. All rights reserved.