Figure 5.
Ca++ dependence of current amplitude in the presence of the endogenous modulator in a cone outer segment membrane patch. Currents, activated by changing membrane voltage from 0 to −40 mV, were repeatedly measured in the same patch in the presence of 60 μM cGMP, 20 μM Ca++, and 100 μM Mg++ after 60-s exposure to solutions containing progressively lower Ca++ concentrations. Data points were normalized by dividing current amplitude measured after each Ca++ concentration tested (I) by the amplitude measured after exposure to a Ca++ free solution (EDTA/EGTA solution) (I0). The data point on the far left indicates I0. This is the maximum possible current since repeated washes in EDTA/EGTA solution did not result in any additional current enhancement.