Intra and extracellular surface charges near Ca2+ channels in neurons and neuroblastoma cells

Abstract

The properties of low (LVA) and high (HVA) voltage-activated calcium currents were investigated in rat sensory neurons and a murine neuroblastoma cell line exposed to various concentrations of intra- or extracellular monovalent ([c+]i/o) and trivalent ([c3+]i/o) cations. In neurons, when [c+]i was changed from 150 to 20 mM, positive shifts of 18-28 mV were observed in activation curves of both LVA and HVA currents, as well as in LVA inactivation curves. Extracellularly, in divalent-free solutions, [c+]o of 20-50 mM produced medium (12-22 mV) negative shifts of the LVA channel properties. These data were used to estimate, by a "screening" model, a negative surface charge density around neuron's calcium channels of 1/1,000 and 1/1,325 eA-2 at the outside or inside face, respectively. In the presence of physiological concentrations of divalent cations, [c+]o of 20-60 mM caused smaller (4-11 mV) negative shifts of the activation and inactivation curves, which can be explained by assuming a partial neutralization of negative charges by divalent cations. By applying the above procedure to LVA channels of neuroblastoma cells, the ratio of extra- to intracellular surface charge density turned out to be more than tenfold higher than in neurons. Effects produced by [c3+]i/o were not in agreement with expectations based on screening or binding models.

Surface Charge and Lanthanum Block of Calcium Current in Bullfrog Sympathetic Neurons

“…When ionic strength is varied, ⌬ depends on in a biphasic manner, so a small ⌬ might reflect either a very low or a very high (Becchetti et al, 1992;Zhou and Jones, 1995). For the best solution with low (1 e Ϫ /4020 Å 2 , Table 2), the calculated ⌬ was Ϫ7.3 mV for the normal versus low ionic strength comparison, and ϩ1.4 mV for normal versus high ionic strength, comparable to the observed values (Table 2).…”

Calcium Protects Differentiating Neuroblastoma Cells during 50Hz Electromagnetic Radiation

“…We investigated the possibility that BT2cAMP and a 120-T 50-Hz magnetic field could interact antagonistically during the differentiating process by affecting the membrane surface charges. To this end we monitored the activation properties of the low-threshold Ca current (Becchetti et al, 1992) in undifferentiated NG108-15 cells challenged by BT2cAMP and/or an electromagnetic field. In the example in Fig.…”

External pH effects on the depolarization-activated K channels in guard cell protoplasts of Vicia faba.

“…Indeed, we estimated the average spacing between the negative charges in the vicinity of the KD channel gates in Vicia as 39 fi~, considerably larger than in the above examples. (In an interesting contrast to the animal K channel, recent analysis of external surface charge near a neuronal Ca channel reveals their large spacing: ~33 A [Becchetti et al, 1992]). A possible interpretation of these differences may be that those parts of the channel protein that contribute to the negative surface charge in the animal K channel (reviewed by Hille, 1992), are different in the KD channel in the plant cell protoplast.…”

“…7 and 8 into a polynomial, derived the roots from the coefficients of the polynomial for each experimental value of pH, and minimized the difference between the observed E0 (mean values) and that calculated from the larger of the two positive solutions of the polynomial (see also Becchetti, Arcangeli, Del Bene, Olivotto, and Wanke, 1992). To find the polynome roots, we used the Fortran subroutine C02AGF from the commercially available NAG library (from the National Algorithm Group, United Kingdom; releases 14 and 15).…”