Abstract

Objective: To determine the effect of arachnotoxin (ATx), a venom extracted from the Chilean spider Latrodectus mactans, on intracellular calcium ([Ca2+]i) and pH (pHi) in capacitated human spermatozoa. Design: Spermatozoa were collected from fertile adult men (n = 8). Mobile spermatozoa were collected by the "swim up" technique and stimulated with the crude extract of ATx and with progesterone (P). Setting: Hospital of the Federal University of São Paulo, São Paulo, Brazil. Main Outcome Measure(s): [Ca2+]i was measured in fura2-AM-loaded spermatozoa, and pHi was measured in spermatozoa loaded with the pH-sensitive dye [(2′,7′)-bis (carboxymethyl)-(5,6)-carboxyfluorescein]-AM (BCECF). Result(s): The ATx and P induced a biphasic change in [Ca2+]i consisting of a peak followed by a small but sustained elevation. The response to ATx was greatly reduced by pretreatment with P. The ATx caused intracellular acidification, whereas P induced alkalinization. Blockade of the NA+/H+ exchanger with ethylisopropylamiloride (EIPA) sharply increased ATx-induced acidification. Conclusion(s): Arachnotoxin increased [Ca2+]i through the opening of calcium channels and release of calcium from intracellular stores. The ATx reduced pHi in human sperm, possibly by inhibiting the Na+/H+ exchanger. © 2007 American Society for Reproductive Medicine.