Localization of Thermoreceptor Systems that Induce Step‐Up and Step‐Down Thermophobic Responses and Switching in the Dominance of These Systems in Blepharisma

Abstract

The distribution of thermoreceptor systems that initiate step‐up and step‐down thermophobic responses in bisected cells of Blepharisma was examined. Anterior cell fragments responded by ciliary reversal to a step‐down in temperature and by repression of spontaneous ciliary reversal to a step‐up. Posterior fragments responded by ciliary reversal to a step‐up in thermal stimulation and by repression of spontaneous ciliary reversal in response to step‐down stimulation. Results indicate that two kinds of thermoreceptor systems exist in the anterior half of each cell; one is responsible for ciliary reversal induced by step‐down stimulation, and the other is responsible for repression of the ciliary reversal caused by step‐up thermal stimulation. Likewise, there are also two kinds of thermoreceptor systems in the posterior half of the cell; one is responsible for ciliary reversal in response to a step‐up in temperature, and the other is responsible for the repression of ciliary reversal on a step‐down in thermal stimulation. Below about 27°C, intact cells showed ciliary reversal only when a step‐down in thermal stimulation occurred, while above about 27°C cells only responded to a step‐up in thermal stimulation. At about 27°C there was a switch in the dominant response from the anterior to the posterior half of an individual cell.