Ca2+ permeability of mouse and chick nicotinic acetylcholine receptors expressed in transiently transfected human cells - PubMed (original) (raw)

A, fluorescence transients (top) and whole-cell currents (bottom) evoked by nicotine applications (filled bars) in a cell expressing αβεδ nAChRs exposed to the indicated Ca2+ concentrations. Filled area represents current integral used to calculate F/Q ratio. B, F/Q relationship of I_Nic obtained by fitting the single F/Q values (1 every 50 ms) of Δ_F/F and current integral, Q, during nicotine application. F/Q ratio of _I_Nic at 2 m

m

Ca2+ (F/_Q_2, ▪) is normalized to that at 110 m

m

Ca2+ (F/_Q_110, ○) to determine _P_f (5.2 % in this case). C, the same F/_Q_110 as in B, illustrated up to larger values of Q and on an expanded horizontal scale. Note the saturation of the F/_Q_110 relation with the increase of current integral. D, relationship between F/_Q_110 and the peak amplitude of _I_Nic (at 110 m

m

Ca2+). Each point represents the F/Q calibration of a single cell. Note the decrease in F/_Q_110 ratio with the increase in current size. The dotted line at 150 pA represents the upper limit value of _I_Nic in isotonic Ca2+ accepted for F/_Q_110 determination. E, measurement of _P_f for fetal muscle nAChRs, using different fluo-3 concentrations in the recording pipette (means ±

s.e.m.

, n = 6). Values obtained by cell-by-cell calibration, □; _P_f values obtained at 250 μ

m

fluo-3, normalizing mean F/Q values at 2 m

m

to those at 110 m

m

Ca2+ (n = 13), ▪.