In vitro development of P- and R-like calcium currents in insect (Periplaneta americana) embryonic brain neurons.

Voltage-gated calcium currents are important for the survival and growth of embryonic cockroach brain neurons in primary culture. In the present experiments, we have studied, using the patch-clamp technique, the evolution with time in culture of the voltage-dependency and of the pharmacological properties of the calcium conductance of these neurons during the formation of a network. We have observed a progressive increase of the high-voltage-activated calcium conductance and a 10mV shift of the voltage-dependency of activation towards more negative potentials. The proportion of the R-like calcium current component increased during network formation. At the same time, the highly omega-AgaTxIVA-sensitive P-like component of the current is progressively replaced by a component which is less sensitive to the toxin. The origin and functional implications of these modifications are discussed.