Properties and development of calcium currents in embryonic cockroach neurons

In freshly dissociated neurons from embryonic cockroach (Periplaneta americ ana L.) brains, voltage-dependent calcium currents appear early in developm ent (E14). Their intensity increases progressively during embryonic life un til eclosion (E35). Their time course and voltage dependency are characteri stic 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 E2 3. Their sensitivity to omega -AgaTx-IVA and omega -CgTx-GVIA and insensiti vity to both amiloride and isradipine indicate that the corresponding chann els are of the P/Q and N types. These channels, as well as a small proporti on of toxin-resistant (R) channels (about 20%), are blocked by mibefradil a nd verapamil. The physiological significance of these currents and their mo difications during embryonic life is discussed. (C) 2000 Elsevier Science I reland Ltd. All rights reserved.