Wicher, Dieter, and Heinz Penzlin. Ca2+currents in central insect neurons: electrophysiological and pharmacological properties. J. Neurophysiol. 77: 186–199, 1997. Ca2+currents in dorsal unpaired median (DUM) neurons isolated from the fifth abdominal ganglion of the cockroach Periplaneta americana were investigated with the whole cell patch-clamp technique. On the basis of kinetic and pharmacological properties, two different Ca2+currents were separated in these cells: mid/low-voltage-activated (M-LVA) currents and high-voltage-activated (HVA) currents. M-LVA currents had an activation threshold of −50 mV and reached maximal peak values at −10 mV. They were sensitive to depolarized holding potentials and decayed very rapidly. The decay was largely Ca2+dependent. M-LVA currents were effectively blocked by Cd2+median inhibiting concentration (IC50= 9 μM), but they also had a remarkable sensitivity to Ni2+(IC50= 19 μM). M-LVA currents were insensitive to vertebrate LVA channel blockers like flunarizine and amiloride. The currents were, however, potently blocked by ω-conotoxin MVIIC (1 μM) and ω-agatoxin IVA (50 nM). The blocking effects of ω-toxins developed fast (time constant τ = 15 s) and were fully reversible after wash. HVA currents activated positive to −30 mV and showed maximal peak currents at +10 mV. They were resistant to depolarized holding potentials up to −50 mV and decayed in a less pronounced manner than M-LVA currents. HVA currents were potently blocked by Cd2+(IC50= 5 μM) but less affected by Ni2+(IC50= 40 μM). These currents were reduced by phenylalkylamines like verapamil (10 μM) and benzothiazepines like diltiazem (10 μM), but they were insensitive to dihydropyridines like nifedipine (10 μM) and BAY K 8644 (10 μM). Furthermore, HVA currents were sensitive to ω-conotoxin GVIA (1 μM). The toxin-induced reduction of currents appeared slowly (τ ∼ 120 s) and the recovery after wash was incomplete in most cases. The dihydropyridine insensitivity of the phenylalkylamine-sensitive HVA currents is a property the cockroach DUM cells share with other invertebrate neurons. Compared with Ca2+currents in vertebrates, the DUM neuron currents differ considerably from the presently known types. Although there are some similarities concerning kinetics, the pharmacological profile of the cockroach Ca2+currents especially is very different from profiles already described for vertebrate currents.

Wicher, D., & Penzlin, H. (1997). Ca2+Currents in Central Insect Neurons: Electrophysiological and Pharmacological Properties. Journal of Neurophysiology, 77(1), 186–199.