Octopamine potentiates intracellular Na+ and Cl- reductions during cell volume regulation in Limulus exposed to hypoosmotic stress.

The biogenic amine octopamine (OCT) appears to be involved in cell volume regulation in the horseshoe crab, Limulus polyphemus, during hypoosmotic stress. OCT is present in relatively large amounts (160 nmoles/g dry wt) in the cardiac ganglion. Furthermore, OCT is released from the isolated ganglion during exposure to hypoosmotic media. This release is reflected in the elevation of blood OCT concentrations from basal levels of 4 X 10(-9) M reaching 1.2 X 10(-8) M within 72 h of exposure of animals to hypoosmotic media. The circulating OCT potentiates the hypoosmotically-induced reductions of intracellular Na+ and Cl- by a ouabain-sensitive mechanism which complements the main ion regulating (ouabain-insensitive) mechanisms utilized during cell volume recovery.