Setting the theoretical fit parameters. Theoretical parameters were created on the basis of related real data on heterotetrameric CNG channels (Schirmeyer et al., 2021; Benndorf et al., 2022; for details see Eqs. 23, 24, 25, 27, 29, and 32 in the supplemental text at the end of the PDF). The set parameters are termed throughout as true parameters, x_i,tr. The saturated colors indicate parameters at respective upper and lower borders and the shaded colors parameters with interpolated values.