Table IV

Parameters of Dim Flash Responses in Ringer's and Prediction of Recovery Shift Due to Cyclase Activation

Rodτcτ′ndBCa,restΔT0.8ΔTcyclaseΔTresidual
sssss
a1.40.43156.65.51.1
b1.80.37186.05.51.5
c1.30.73287.75.72.0
d1.70.31107.64.82.8
e1.40.33136.54.42.1
f1.40.32145.74.31.4
g1.20.27 74.04.5−0.5
h1.20.35185.74.51.2
i1.70.41257.8*5.72.1
j1.70.35275.5*4.60.9
1.5 ± 0.20.39 ± 0.1217.5 ± 7.26.2 ± 1.25.0 ± 0.61.5 ± 0.9
  • Column 1 identifies the rod. Columns 2–4 give the parameters of the model used to fit the low intensity responses in Ringer's, as illustrated in Figs. 11–13; the value of the amplification constant used is given in Table II, and in all cases the Hill coefficient was set to nH = 2. τc′ is the value of the larger time constant of the disc-associated reactions, and τ′nd the shorter time constant (Eq. 5). Column 4 gives the value of α′max = αmax/cGdark, the maximal rate of guanylyl cyclase activity divided by the concentration of cGMP in the dark (see ii). Column 5 gives the observed shift at the point of 80% recovery (20% response amplitude) between saturating responses obtained in choline and in Ringer's. Column 6 gives the shift predicted on the assumption that cyclase activation alone is responsible, calculated with Eq. 16. Column 7 gives the residual shift; i.e., the observed minus the predicted shift.  

  • *  Rods i and j were recorded from in 0-Ca2+ choline, and for the reasons given in the notes to Table II, we were unable to measure ΔT0.8 and have instead substituted ΔT0.5.