Some In Vivo and In Vitro Characteristics of Aplysia Californica Haemolymph*

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Abstract
The nervous system of the opisthobranch mollusc, Aplysia californica Cooper has been extensively studied and a great deal is known about the electrophysiological properties of a number of identifiable neurones (see Kandel, 1976, 1979). A variety of synaptic and electrical connections have been mapped, permitting identification of the mode in which nervous control is exerted over certain motor functions. Substantially less is known regarding other physiological systems of Aplysia (Kandel, 1979), particularly the respiratory system, and this limits the description of how nervous control is affected by internal physiological state. Chalazonitis & Nahas (1965) reported data for haemolymph pH, CO2 tension and O2 tension in the related species, Aplysia fasciata, and Bevelaqua et al. (1975) identified the respiratory pigment, haemocyanin, in the haemolymph of A. californica. However, there has been no detailed study of in vivo oxygen levels or acid-base status of A. californica. Neither are there any data for the in vitro properties of A. californica haemolymph, such as oxygen carrying capacity, oxygen affinity or buffering properties. Such data are of particular importance in A. californica, for two reasons. Firstly, motor function, such as the often-studied gill withdrawal reflex, may be directly influenced by factors such as pH, or as are the respiratory performances of other marine invertebrates (Mangum & Burnett, 1975; McMahon & Wilkens, 1975; Bayne, 1976; Batterton & Cameron, 1978). Secondly, Chalazonitis (1974) has shown clearly that membrane potential, spike frequency and membrane resistance of many single cells in A. fasciata are directly affected by pH, and of the bathing fluid. Therefore, the present study was undertaken to describe some of the in vivo and in vitro properties of the haemolymph of A. californica with regards to acid-base status and oxygenation characteristics.