Characteristics of Ca2+, Mg2+-dependent ATP hydrolysis in sperm cells of infertile men

Abstract

Disturbances of fertilizing potential of spermatozoa are closely associated with dysfunction of ion-transporting ATPases, in particular Ca²⁺, Mg²⁺-АТРase. Reduced activity of tapsigargin-resistant and tapsigargin-sensitive Ca²⁺, Mg²⁺-АТРase leads to disruption of Ca²⁺-homeostasis and is characteristic for abnormal spermatozoa (pathoospermia). In order to study the peculiarities of action of Ca²⁺, Mg²⁺-АТРase, we determined the initial reaction rate, the maximum (plateau) amount of the reaction product and the cha­­racteristic reaction time. To determine these kinetic parameters of Ca²⁺, Mg²⁺-dependent hydrolysis of ATP catalyzed by Ca²⁺, Mg²⁺-ATPase, the dynamics of product accumulation of the ATP-hydrolases reaction was studied. The obtained curves were linearized in the coordinates {P/t; P}. Analyzing the changes in the activity of Ca²⁺, Mg²⁺-ATPase, the kinetics of primary-active transport of calcium ions through the plasma membrane and membranes of intracellular Ca²⁺-stores in saponin-permeabilized spermatozoa of infertile men was studied. It was shown that in normozoospermic samples, the transport of Ca²⁺ ions through the plasma membrane is characterized by a higher capacity than through the membranes of intracellular Ca²⁺-stores, but it occurs with practically the same initial velocity and characteristic reaction time. It was found that in pathospermic samples, transport of Ca²⁺ ions with the participation of both components of Ca²⁺, Mg²⁺-ATPase occurs less intensively and is characterized by a lower capacity compared to spermatozoa of men with preserved fertility. Specific changes in the kinetic parameters of Ca²⁺, Mg²⁺-dependent hydrolysis of ATP lead to inhibition of tapsigargin-resistant and tapsigargin-sensitive Ca²⁺, Mg²⁺-ATPase activity and cause a decrease in fertilizing potential of spermatozoa.   Keywords: Ca²⁺, Mg²⁺-ATPase, ATP hydrolysis, spermatozoa, male infertility, pathospermia