Signal transduction in red blood cells of the lizards Ameiva ameiva and Tupinambis merianae (Squamata, Teiidae)

The fluorescent calcium probe, Fluo-3, AM was used to measure the intracellular calcium concentration in red blood cells (RBCs) of the teiid lizards Ameiva ameiva and Tupinambis merianae. The cytosolic [Ca2+] is maintained around 20 nM and the cells contain membrane-bound Ca2+ pools. One pool appears to be identifiable with the endoplasmic reticulum (ER) inasmuch as addition of the sarco-endoplasmic reticulum Ca2+ ATPase, SERCA, inhibitor thapsigargin induces an increase in cytosolic [Ca2+] both in the presence and in the absence of extracellular Ca2+ In addition to the ER, an acidic compartment appears to be involved in Ca2+ storage, as collapse of intracellular pH gradients by monensin, a Na+-H+ exchanger, and nigericin, a K+-H+ exchanger, induce the release of Ca2+ from internal pools, A vacuolar H+ pump, sensitive to NBD-Cl and bafilomycin appears to be necessary to load the acidic Ca2+ pools. Finally, the purinergic agonist ATP triggers a rapid and transient increase of [Ca2+](c) in the cells from both lizard species, mostly by mobilization of the cation from internal stores. (C) 2001 Harcourt Publishers Ltd.