Non–Voltage-Gated Ca ²⁺ Influx Through Mechanosensitive Ion Channels in Aortic Baroreceptor Neurons

Abstract

The mechanisms underlying mechanotransduction in baroreceptor neurons (BRNs) are undefined. In this study, we specifically identified aortic baroreceptor neurons in primary neuronal cell cultures from nodose ganglia of rats. Aortic baroreceptor neurons were identified by labeling their soma with the fluorescent dye 1,1'-dioleyl-3,3,3',3'-tetramethylin-docarbocyanine (DiI) applied to the aortic arch. Using Ca2+ imaging with fura 2, we examined these BRNs for evidence of Ca2+ influx and determined its mechanosensitivity and voltage dependence. Mechanical stimuli were produced by ejecting buffer from a micropipette onto the cell surface with a pneumatic picopump, producing a shift in the center of mass of the cell that was related to intensity of stimulation. Ninety-three percent of DiI-labeled neurons responded to mechanical stimulation with an increase in [Ca2+]i. The magnitude of the increases in [Ca2+]i was directly related to the intensity of the stimulus and required the presence of external Ca2+. The trivalent cations Gd3+ or La3+ in equimolar concentrations (20 mumol/L) eliminated the K(+)-induced rises in [Ca2+]i, demonstrating that both trivalent cations are equally effective at blocking voltage-gated Ca2+ channels in these baroreceptor neurons. In contrast, the mechanically induced increases in [Ca2+]i were blocked by Gd3+ (20 mumol/L) only and not by La3+ (20 mumol/L). Stretch-activated channels (SACs) have been shown in other preparations to be blocked by Gd3+ specifically. Our data demonstrate that (1) BRNs, specifically identified as projecting to the aortic arch, have ion channels that are sensitive to mechanical stimuli; (2) mechanically induced Ca2+ influx in these cells is mediated by a Gd(3+)-sensitive ion channel and not by voltage-gated Ca2+ channels; (3) the magnitude of the Ca2+ influx is dependent on the intensity of the stimulus and the degree and duration of deformation; and (4) repeated stimuli of the same intensity result in comparable increases in [Ca2+]i. We conclude that mechanical stimulation increases Ca2+ influx into aortic BRNs independent of voltage-gated Ca2+ channels. The results suggest that Gd(3+)-sensitive SACs are the mechanoelectrical transducers in baroreceptors.

Mechanism for action of electromagnetic fields on cells

“…It seems possible that the oscillating ions during forced-vibration can also exert mechanical forces-pressure, on the plasma membrane, able to upset the membraneÕs electrochemical balance, under certain conditions, by opening or closing mechanically gated channel proteins, like some Ca þ2 influx channels [61]. But of course this can be a subject of a separate research, based on the present theoretical model of the ionsÕ forced-vibration which we have presented here.…”

Serotonin 5-HT3 receptors on mechanosensitive neurons with cardiac afferents

“…Neither of these substances significantly affected the responses of aortic baroreceptor neurons to hypoosmotic mechanical stress, suggesting that the gadolinium effect could be due to its action on mechanosensitive channels and is not mediated by calcium channels. However, one should keep in mind that gadolinium has been reported to block increases in [Ca 2ϩ ], produced by mechanical stimulation of nodose neurons in vitro (25,27).…”

Neuronal Prostacyclin Is an Autocrine Regulator of Arterial Baroreceptor Activity

“…7,19 DiI fluorescence of labeled BRNs was detected using Rhodamine filter set on the stage of Diaphot TMD Nikon microscope (Nikon). The neurons were isolated and cultured as described previously 7,19 -22 (please see http://hyper.ahajournals.org).…”