LOCALIZATION OF THERMORECEPTOR SYSTEMS THAT INDUCE STEP-UP AND STEP-DOWN THERMOPHOBIC RESPONSES AND SWITCHING IN THE DOMINANCE OF THESE SYSTEMS IN BLEPHARISMA

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-degrees-C, intact cells showed ciliary reversal only when a step-down in thermal stimulation occurred, while above about 27-degrees-C cells only responded to a step-up in thermal stimulation. At about 27-degrees-C there was a switch in the dominant response from the anterior to the posterior half of an individual cell.