Noise and single channels activated by excitatory amino acids in rat cerebellar granule neurones.

Abstract

SUMMARY1. Glutamate-receptor ion channels in rat cerebellar granule cells maintained in explant cultures have been investigated with patch-clamp methods. Properties of these channels were determined from noise analysis of whole-cell currents and from noise and single-channel currents recorded in outside-out membrane patches.2. Glutamate (10-20 /LM) evoked two types of response. Some granule cells gave small inward currents accompanied by clear increases in current noise ('large noise' responses), whereas other cells gave larger inward currents and small noise increases ('small noise' responses).3. A mean single-channel conductance (y) of 46-6 pS was estimated for glutamate from four 'large noise' cells. A mean y value of 8-4 pS was estimated for seven other 'large noise' cells. The results suggest that in these latter cells glutamate activated both large (_ 50 pS) and small conductance (-140 fS) channels. 5. Large single-channel currents were evoked by glutamate, aspartate and NMDA in outside-out patches. The mean conductance values obtained for the largest amplitude openings were: y(glutamate) = 49-5 pS, y(aspartate) = 51-5 pS, and y(NMDA) = 53'0 pS. For each agonist, these 50 pS openings comprised 75-85 % of the completely resolved currents in each patch. Openings to 40 and 30pS conductance levels accounted for 10-15 % and 3-7 % of the total, and the presence of apparently direct transitions between these levels and the 50 pS level suggests they are sublevels of the same multi-conductance channels.6. A mean channel conductance of 22-9 pS was estimated from noise evoked by quisqualate (10-30 /SM). Single-channel currents were examined in four patches. In two, quisqualate evoked predominantly small currents of two amplitudes, y = 8&4 pS and 16-5 pS; some 50 pS openings were also present. In the other two patches, most openings were 50 pS events.7. Granule cells gave inward currents to, kainate S. G. CULL-CANDY AND OTHERS channel currents evoked by kainate were of smaller amplitude, with mean conductances of y = 8'1 and 15-1 pS. Kainate also activated 50 pS channels and produced some 30 and 40 pS openings.8. A mean single-channel conductance of 140 fS was estimated from 'small noise' whole-cell currents evoked by glutamate (10-20 /tM). Spectra of noise produced by glutamate in outside-out patches from 'small noise' cells were similar to spectra of noise produced in patches by kainate. 9. Our results indicate that granule cells possess at least three types of glutamatereceptor channels. One type has a maximum conductance of approximately 50 pS;it displays multiple open levels and appears to be activated selectively by aspartate and NMDA. Openings with conductances of 8 and 15 pS are produced by kainate and quisqualate in large numbers and it appears unlikely they are sublevels of the 50 pS channels. Channels with an estimated conductance of 140 fS appear to be present at high density in most granule cells. These channels are activated by glutamate and kainate, but not by aspartate or NMDA to any significant exte...

The properties of 5‐HT3 receptors in clonal cell lines studied by patch‐clamp techniques

“…Such a mechanism is not unprecedented. Glutamate, or kainate can activate cationconducting channels with a conductance as low as 140 fS in cerebellar granule cells and membrane patches excised from them (Cull-Candy & Ogden, 1985;Cull-Candy et al, 1988). Additionally, in rat spinal neurones kainate can elicit currents which appear only as an increase in the membrane noise of outside-out patches .…”

“…Instead it is now clear that in addition to a most frequently observed main conductance state, such channels may open to states of higher or lower conductance (e.g. Cull-Candy & Usowicz, 1987;Jahr & Stevens, 1987). Fluctuation analysis is likely to provide a weighted-mean estimate of channel conductance that is influenced by the relative frequency of all conducting states.…”

“…Ionophoretic pipettes contained 20 mm 5-HT in twice distilled deionized water (pH 3.5-4.0) and had resistances > 80MQ A constant current pump based on the design of Dreyer & Peper (1974) The variance analysis method was used to estimate the single channel conductance (Marty et al, 1984;Cull-Candy et al, 1988;. The record was split into a series of 0.5 s blocks (512 samples) with variance and mean current calculated for each block from the equation:…”

Inorganic mercury modifies Ca2+ signals, triggers apoptosis and potentiates NMDA toxicity in cerebellar granule neurons

“…As model system, we selected primary cultures of rat cerebellar granule cells (CGCs). After a few days in culture, CGCs, the most abundant neuronal population in the cerebellum (D'Mello et al, 1993), express glutamate receptors of the NMDA subtype and can selectively release L-glutamate and Laspartate upon depolarization (Cull-Candy et al, 1988). These characteristics enabled us to study the interference of Hg 2+ with Ca 2+ signalling elicited by either high K + or NMDA and to investigate the implication of this interaction for cell survival.…”

Glutamate acting on NMDA receptors stimulates neurite outgrowth from cerebellar granule cells

“…In addition, these cells possess NMDA receptors [13] which are linked to channels with a conductance of 50 pS [14,15]. We have examined the possibility that endogenous glutamate acting through NMDA receptors stimulates neurite outgrowth from cerebellar granule cells in culture.…”