Voltage dependence of the [Ca2+](i) oscillations system, in the Mg2+ -stimulated oocyte of the prawn Palaemon serratus.

By voltage-clamp technique and simultaneous [Ca2+](i)measurements, we studied the modifications, induced by changes in membrane voltage, in the pattern of the [Ca2+](i)oscillation period, displayed by the Mg2+-stimulated oocyte of the prawn Palaemon serratus. When the Mg2+-stimulated oocytes were voltage clamped at 0mV, they developed a [Ca2+](i)signal with a more pronounced oscillatory pattern than that obtained on unclamped oocytes. Indeed, they displayed a first peak followed by a series of sharp [Ca2+](i)transients and a prominent [Ca2+](i)oscillatory plateau. By contrast, oocytes voltage clamped at - 60mV showed a first peak followed by a stable high [Ca2+](i)level forming a long continuous plateau devoid of oscillations. By using caged InsP3, we established that the ER InsP3 receptor is not voltage sensitive. Paradoxically, we showed the voltage sensitivity of the Mg2+ receptor-signal transduction system which is more reactive to Mg2+ ions at -60mV than at 0mV. Using different calmodulin inhibitors of the PM CA pump such as trifluoperazin (100microM), W-7 (50microM) and calmidazolium (50microM), we suppressed the [Ca2+](i)oscillatory pattern in oocytes voltage clamped at 0mV. From these results we propose that this special voltage-dependent oscillatory system could be regulated by a significant involvement of the electrogenic PM CA pump.