Simon Levy

Boston University | BU · Department of Physiology and Biophysics

Although store-operated Ca(2+) influx has been well-studied in nonneuronal cells, an understanding of its nature in neurons remains poor. In the bag cell neurons of Aplysia californica, prior work has suggested that a Ca(2+) entry pathway can be activated by Ca(2+) store depletion. Using fura-based imaging of intracellular Ca(2+) in cultured bag ce...

Drosophila transient receptor potential (TRP) is a prototypical member of a novel family of channel proteins underlying phosphoinositide-mediated Ca(2+) entry. Although the initial stages of this signaling cascade are well known, downstream events leading to the opening of the TRP channels are still obscure. In the present study we applied patch-cl...

Injections of inositol 1,4,5 triphosphate (InsP3) into Limulus ventral photoreceptors give rise to a rapid depolarization and an elevation of intracellular calcium concentration (Cai). This response to InsP3 is followed by a period of desensitization that persists as long as Cai remains elevated (feedback inhibition). Limulus ventral photoreceptors...

1. Transient stimulation of an afferent input to the bag cell neurons of Aplysia californica triggers a 30-min period of spontaneous firing termed the afterdischarge. Measurement of free calcium ion concentrations using calcium-sensitive electrodes revealed a biphasic pattern of elevation of intracellular calcium levels during the afterdischarge. B...

Selected neurons of the abdominal ganglion of Aplysia californica were voltage-clamped and intracellular free Ca [( Ca2+]i) and Na [( Na+]i) concentrations were monitored with ion selective microelectrodes. Reducing [Na+]o from 500 mM (normal seawater, NSW) to 5 mM resulted in a decrease of the potential measured by the Ca electrode (VCa). Increasi...

Microvillar photoreceptors of invertebrates exhibit a light-induced rise in the intracellular concentration of free calcium (Cai) that results in part from release of calcium from an intracellular compartment. This light-induced release of calcium appears to result from a cascade of reactions that involve rhodopsin, a GTP-binding protein and a phos...

Unlike most secretory cells, high extracellular Ca2+ inhibits, rather than stimulates, PTH release from parathyroid cells. To gain more direct access to the potentially unique secretory apparatus of this cell type, we developed techniques for permeabilizing parathyroid cells using electroshock. Exposure of dispersed bovine parathyroid cells to five...

The ability of the Ca2+-selective microelectrode to measure fast Ca2+ transients intracellularly is reviewed. In vitro, Ca microelectrodes can respond to Ca2+ injections with time to peaks as small as 40 ms. We present methods to improve the dynamic response of Ca microelectrodes and to make Ca-buffered solutions in high ionic strength. Examples of...

Calibration of ion-selective microelectrodes involves delivering and measuring the potential of several different solutions both before and after intracellular measurement. A microprocessor-controlled system is described which completely automates that tedious process. The microcomputer controls the delivery of the calibration solutions and prints...

The possible role of Ca ions in mediating the drop in sensitivity associated with light adaptation in Limulus ventral photoreceptors was assessed by simultaneously measuring the sensitivity to light and the intracellular free Ca concentration (Cai); the latter was measured by using Ca-selective microelectrodes. In dark-adapted photoreceptors, the m...

Selected neurones of the abdominal ganglion of Aplysia californica were voltage clamped, injected with the Ca2+-indicator dye Arsenazo III, and impaled with Ca2+-selective micro-electrodes. Measurements of the absorbance signal (Arsenazo III) and Ca2+ micro-electrode potential during and following voltage-dependent Ca2+ influx (induced by voltage-c...

When neurones are active there is an entry of Na+, which must subsequently be pumped out, and an increase in their oxygen consumption rate (Qo2). The Na+ pump derives its energy from ATP, splitting it into ADP and Pi, and it has reasonably been proposed that the changes in concentrations of ATP, ADP and Pi lead to a stimulation of the O2 consumptio...

Summary The intracellular pH of the Limulus ventral photoreceptor was measured with a double-barrelled pH microelectrode and found to be 7.01±0.04 SE (n=9).