Interplay between Ca2+release and Ca2+influx underlies localized hyperpolarization-induced [Ca2+]iwaves in prostatic cells

Abstract

Calcium seems to be a major second messenger involved in the regulation of prostatic cell functions, but the mechanisms underlying its control are poorly understood. We investigated spatiotemporal aspects of Ca2+signals in the LNCaP cell line, a model of androgen-dependent prostatic cells, by using non-invasive external electric field pulses that hyperpolarize the anode facing membrane and depolarize the membrane facing the cathode. Using high-speed fluo-3 confocal imaging, we found that an electric field pulse (10–15 V/cm, 1–5 mA, 5 ms) initiated rapidly, at the hyperpolarized end of the cell, a propagated [Ca2+]iwave which spread through the cell with a constant amplitude and an average velocity of about 20 μm/s. As evidenced by the total wave inhibition either by the block of Ca2+entry or the depletion of Ca2+stores by thapsigargin, a specific Ca2+-ATPase inhibitor, the [Ca2+]iwave initiation may imply a localized Ca2+influx linked to a focal auto-regenerative process of Ca2+release. Using different external Ca2+and Ca2+entry blockers concentrations, Mn2+quenching of fluo-3 and fura-2 fluorescence and inhibitors of InsP3production, we found evidence that the [Ca2+]iwave progression required, in the presence of basal levels of InsP3, an interplay between Ca2+release from InsP3-sensitive Ca2+stores and Ca2+influx through channels possibly activated by the [Ca2+]irise.