Examples of Markov Models
(A) Three-state scheme considered in the text.
(B) Best-fit model derived by Vandenberg and Bezanilla  for sodium currents in the squid giant axon using least-squares fitting to single-channel data.
(C) T-type calcium model by Frazier et al.  reflecting structural constraints derived by exponential fitting of macroscopic currents. Open circles represent open (conducting) states. Filled circles and filled squares are closed and inactivated states, respectively. The distinction does not affect the structure or behavior of the model, but they are useful labels to tie the scheme to the phenomenology of channel behavior.