Observations on the cytolemma of the olfactory receptor cell in the newt. 1. Freeze replica analysis.

The fine structure of the cytolemma of olfactory receptor cells in the newt was studied by the freeze-fracture replica method. Two kinds of receptor cells were recognized, namely ciliated cells (ciliary type) and non-ciliated cells (microvilli type). The cytolemma of olfactory knobs as well as their processes from both types of receptor cells showed an abundance of large membrane particles 80 approximately 110 A in diameter. The large square aggregation of membrane particles, 0.1 x 0.1 micron to 0.2 x 0.3 micron in size, consisting of 50 approximately 100 cuboidal subunits, were found in the cytolemma of the dendrite. A structural model of aggregation is presented. The soma of the receptor cell revealed large pitted membrane particles about 140 A in diameter. These particles are possibly the morphologic counterpart to ionophores which have been proposed by electrophysiological studies.