ROLE OF P2-PURINERGIC RECEPTORS IN RAT LEYDIG-CELL STEROIDOGENESIS

The present study investigated the effects of extracellular ATP on the intracellular calcium ion concentration ([Ca2+](i)) and testosterone production in isolated adult rat Leydig cells. This nucleotide caused an increase in [Ca2+](i), with a maximal effect at a concentration of 100 mu M ATP, comprising a rapid initial spike followed by a long-last ing plateau. The first rapid spike was dependent on the release of Ca2 + from internal stores, since it also occurred in Ca2+-free medium and was abolished after depletion of internal stores with thapsigargin. T he second, longlasting, phase was dependent on the influx of Ca2+ from the extracellular medium. After 3 h of incubation, extracellular ATP stimulated testosterone secretion in a dose-dependent manner, with a m aximal effect at 100 mu M. Activation of steroidogenesis by ATP was fu lly dependent on the presence of Ca2+ in the external medium. Among di fferent nucleotides, only ATP, adenosine 5'-[gamma-thio]triphosphate, UTP, benzoylbenzoic-ATP and 2-methylthio-ATP were effective in inducin g both the rise in [Ca2+](i) and testosterone secretion. These effects were blocked by preincubation of Leydig cells with oxidized ATP, an i nhibitor of the P2Z-purinergic receptor subtype. These results show th at rat Leydig cells possess P2-purinergic receptors whose activation t riggers an increase in [Ca2+](i) due to the release of Ca2+ from inter nal stores and Ca2+ influx from the external medium. The stimulatory e ffect of extracellular ATP on testosterone secretion seems to be coupl ed to the influx of Ca2+ from the external medium.