ISSN:
1432-1424
Keywords:
receptor-operated Ca2+ influx
;
compound 48/80
;
mast cell
;
current noise
;
stimulus-secretion coupling
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary We analyzed the noise of the inward currents induced by stimulation of rat peritoneal mast cells with compound 48/80 (48/80), a secretagogue, and examined the role of extracellular Ca2+ in generation of the large noise. In the presence of 2 mm Ca2+ in the external solution, the power density spectra of the 48/80-induced inward currents in most cells were fitted with the sum of two Lorentzian functions. The cut-off frequencies (f c) at −50 mV for the low and high frequency components were 16.3 ±7.3 (n = 10) and 180±95 (n = 9) Hz. Involvement of a cationselective channel in the large noise was identified in some cells, but the single channel current amplitude estimated from parameters of the noise varied among cells (0.20–2.47 pA at −50 mV), thereby indicating that the currents were mediated by more than two classes of channel. The low frequency component of the 48/80-induced currents was suppressed by lowering the extracellular Ca2+ concentration to 1 μm with the addition of EGTA, without appreciable changes in the high frequency component. When the extracellular Ca2+ was reduced to 1 μm by EGTA 1 min prior to stimulation, 48/80 induced little or no currents in most cells and small currents in some cells. The power density spectra of the small currents were fitted mainly by a single Lorentzian curve with an f c of 150±5.8 Hz (n = 3). Re-admission of 1.3 mm Ca2+ produced a low frequency part of current noise with an f c of 18.8 (n = 2) Hz. When the extracellular Na+ was totally replaced by N-methyl-d-glucamine or choline in the presence of 2–5 mm Ca2+, the mean current amplitude was smaller than that in the Na+-containing medium, but the power density spectra of the current noise were fitted by a sum of two Lorentzians with f c of 13.7±6.4 (n = 6) and 186±77 (n = 6) Hz. These results suggest that low frequency fluctuation of currents depends on the extracellular Ca2+ and underlies the large noise of the 48/ 80-induced inward currents. The 48/80-induced Ca2+ influx seems to be essential to generate the low frequency fluctuations, and Na+ influx through the cation-selective channel would augment the amplitude of the fluctuation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00231870
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