P2X4 is a candidate mediator of the high-affinity ATP response in spermatogonia. (A) Reverse transcription PCR reveals transcripts for P2rx2, P2rx4, and P2rx7 in both Sertoli–germ cell co-cultures and whole testis preparations at P7. A faint band for P2rx3-encoding cDNA is only amplified from whole testis samples but not co-cultures. Primer pairs generate amplificates of 150–250 bp, respectively. cDNA from whole brain/spinal cord serves as positive control, whereas no template controls are devoid of detectable signals. (B–E) Exemplary whole-cell voltage-clamp recordings of ATP-induced currents (10 µM; 1 s; V_hold = −80 mV; S₁, S₆) under control conditions and during treatment with suramin (10 µM and 100 µM; B), extracellular Cu²⁺ (100 µM; C), reduced pH (6.3; D), and ivermectin (3 µM; E). Altered conditions were established for at least 60 s (preincubation). (F) Bar diagram (means ± SEM) depicting the quantitative analysis of experiments exemplified in B–E. Note the discontinuous ordinate (//). Numbers of cells tested are indicated above bars. Asterisks (*) denote statistical significance, P ≤ 0.01 (paired t test).