Hemocyte adhesion in the California mussel (Mytilus californianus): regulation by adenosine.
On removal from the animal, molluscan hemocytes change from an aggregation-incompetent state to one in which they aggregate and stick avidly to foreign surfaces. Aggregation and substratum adhesion behaviors of Mytilus californianus (California mussel) hemocytes are inhibited reversibly and non-lethally by caffeine. We investigated the mechanistic basis of this inhibition by means of assays that determined the abilities of several compounds to compete or synergize with caffeine in achieving its effect. Adenosine and the adenosine receptor agonists 2-chloro-adenosine or 5'-N-ethylcarboxamido-adenosine reversed caffeine inhibition. In contrast, isobutyl-methyl-xanthine (both an adenosine receptor antagonist and an inhibitor of phosphodiesterase) and the adenosine receptor antagonists cyclo-hexyladenosine and R-N6-phenyl-isopropyladenosine synergized with caffeine to inhibit hemocyte adhesion. Caffeine treatment reduced intracellular cAMP. Alterations in cAMP concentrations in response to caffeine with or without adenosine and adenosine analogues reflected alterations in adhesion behavior in the same drugs. R-N6-phenyl-isopropyladenosine plus caffeine yielded intracellular cAMP levels lower than those in cells treated with caffeine alone. However, both cAMP level and hemocyte adhesion increased when adenosine or 5'-N-ethylcarboxamido-adenosine replaced R-N6-phenyl-isopropyladenosine. This mollusc's hemocytes appear to express adenosine receptors that modulate phagocyte behavioral responses by altering second messenger transduction.
Chen
J H
JH
Department of Zoology, Oregon State University, Corvallis 97331-2914, USA.
Bayne
C J
CJ
D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology*; D000818:Animals; D049872:Bivalvia / Q000187:drug effects / Q000502:physiology*; D002110:Caffeine / Q000494:pharmacology; D002448:Cell Adhesion / Q000187:drug effects; D000242:Cyclic AMP / Q000032:analysis; D006434:Hemocytes / Q000187:drug effects / Q000502:physiology*; D018047:Receptors, Purinergic P1 / Q000187:drug effects
D018047:Receptors, Purinergic P1; D002110:Caffeine; D000242:Cyclic AMP; D000241:Adenosine