ATP increases head volume in capacitated human sperm via a purinergic channel

Scanning ion-conductance microscopy allowed us to document an external Ca²⁺ dependent ATP driven volume increase (ATPVI) in capacitated human sperm heads. We examined the involvement of purinergic receptors (PRs) P2X2R and P2X4R in ATPVI using their co-agonists progesterone and Ivermectin (Iver), and Cu²⁺, which co-activates P2X2Rs and inhibits P2X4Rs. Iver enhanced ATPVI and Cu²⁺ and 5BDBD inhibited it, indicating P2X4Rs contributed to this response. Moreover, Cu²⁺ and 5BDBD inhibited the ATP-induced acrosome reaction (AR) which was enhanced by Iver. ATP increased the concentration of intracellular Ca²⁺ ([Ca²⁺]_i) in >45% of individual sperm, most of which underwent AR monitored using FM4-64. Our findings suggest that human sperm P2X4R activation by ATP increases [Ca²⁺]_i mainly due to Ca²⁺ influx which leads to a sperm head volume increase, likely involving acrosomal swelling, and resulting in AR.