ACID-BASE REGULATION IN PULMONATE MOLLUSKS

Evidence is presented for a role of CO2 in acid-base regulation by air-breathing gastropods. In the land snail Otala lactea, alterations of PCO2 account for pH adjustment during acute temperature change and in compensation for metabolic acidosis. CO2 release from the gastropod lung appears to be more closely coupled with ventilation than is O2 uptake, because O2 uptake is limited to a greater extent by diffusion through the lung epithelium. Cutaneous CO2 release may account for half of CO2 release from active snails, and the loss of this route during withdrawal into the shell partly accounts for elevation of CO2 during dormancy. Further CO2 accumulation and consequent acidosis during dormancy is attributable to hypoventilation of the lung. Although respiratory acidosis appears to be involved in metabolic depression during dormancy, the mechanism of influence on cellular metabolism is unknown and is probably indirect. Unlike the respiration of whole animals, respiration of isolated tissues of Otala is insensitive to PCO2.