Effects of arachnotoxin on intracellular pH and calcium in human spermatozoa

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 (pH(i)) 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.