The carotid body (CB) chemoreceptor cells, m spite of their neural origin, were considered nonexcitable until the late 1980's. The remarkable complexity of the organ, together .
with the small size of type I cells, represented a limitation for conventional intracellular microelectrode recordings, making a definitive electrophysiological study problematic. The neurochemical approach used during the early l980's, following the stimulus-secretion model established in other neurosecretory systems, suggested an important role for the plasma membrane of type I cells in the hypoxic chemotransduction process. Development of iso lated type I cell cultures, together with the use of the patch-damp technique, have brought
direct evidence in support of this idea.1
We now have a general picture about the electrical
properties of these cells, and their excitable character is unequivocally established; they pos sess voltage-dependent ion channels and they are capable of firing action potentials.Al though there is a general agreement in the literature about the basic facts, the details are far from being clear. The role of ionic currents in the transduction process by type I cells has been a matter of discussion, and differences in the results reported by different laboratories are evident. In most of the cases the differences could be interpreted on basis of the fact that . either cells from different species or at different stages of development have been studied, but in sorne cases, the differences have led to the proposal of different hypotheses about the mechanisms of chemotransduction.
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