Properties and development of calcium currents in embryonic cockroach neurons.

In freshly dissociated neurons from embryonic cockroach (Periplaneta americana L.) brains, voltage-dependent calcium currents appear early in development (E14). Their intensity increases progressively during embryonic life until eclosion (E35). Their time course and voltage dependency are characteristic of high voltage activated (HVA) currents although a 10 mV shift of the I/V curve towards more negative potentials was observed between E18 and E23. Their sensitivity to omega-AgaTx-IVA and omega-CgTx-GVIA and insensitivity to both amiloride and isradipine indicate that the corresponding channels are of the P/Q and N types. These channels, as well as a small proportion of toxin-resistant (R) channels (about 20%), are blocked by mibefradil and verapamil. The physiological significance of these currents and their modifications during embryonic life is discussed.