Intracellular ADP modulates the Ca2+ release-activated Ca2+ current in a temperature- and Ca2+-dependent way

The rat basophilic cell line RBL-1 is known to express high levels of the Ca2+ current activated by store depletion, known as Ca2+ release-activated Ca2+ current (I-CRAC), the main Ca2+ influx pathway so far identified in nonexcitable cells. We show here that, as reported in other cell types, metabolic drugs strongly inhibit the Ca2+ influx operated by store depletion in RBL-1 cells also. We have tested the hypothesis that intracellular adenine and/or guanine nucleotide levels act as coupling factors between I-CRAC and eel metabolism. Using the whole cell configuration of the patch-clamp technique, we demonstrate that addition of ADP to the intracellular solution significantly reduces I-CRAC induced by inositol 1,4,5-trisphosphate. This phenomenon differs from other regulatory pathways of I-CRAC since it is highly temperature-dependent, is observable only in the presence of low intracellular Ca2+ buffering capacity, and requires a cytosolic factor(s) which is rapidly lost during cell dialysis, Moreover, the inhibition is specific for ADP and is partially mimicked by ADP beta S and AMP, but not by GDP or GTP.