Differences in the behavior of excitable cells are correlated with differences in function. The electrical properties of a neuron are primarily determined by the array of potassium channels that it expresses. These experiments examined potassium currents in two populations of neurons from the chick embryo. Neurons from the parasympathetic ciliary ganglion can fire action potentials at a very high rate, while neurons from the lumbar sympathetic chain ganglia have a much lower maximum firing rate. The results show that these differences in electrical behavior are primarily due to differences in the potassium currents expressed in the two cell types. Ciliary neurons express a complement of potassium currents that are primarily geared towards the production of rapid repetitive firing. These include: (1) a small A-current; (2) a rapidly activating delayed rectifier; (3) voltage-and calcium-activated potassium channels that also participate in action potential repolarization; and (4) an inward rectifier that helps to repolarize the membrane. By contrast, sympathetic neurons express some potassium currents that inhibit repetitive firing: (1) a large A-current; (2) a slowly activating delayed rectifier; and (3) an M-current that reduces cellular excitability. / Other experiments show that divalent cations have a large effect on the voltage dependence of inactivation of the A-current without affecting any other voltage dependent parameter. The effects of divalent cations take place from outside the cell, a result that is not consistent with models of the inactivation process. These results suggest that these A-channels have a binding site for divalent cations on the external face of the channel. / Additional experiments show that in ciliary ganglion neurons, L-type Ca$\sp{2+}$ channels are preferentially coupled to I$\sb{\rm K\lbrack Ca\rbrack},$ although other Ca$\sp{2+}$ channel types are present. By contrast, in sympathetic neurons, N-type Ca$\sp{2+}$ and in some cases both types of Ca$\sp{2+}$ channels are functionally linked to I$\sb{\rm K\lbrack Ca\rbrack}.$ These results suggest that some neurons have the capacity to preferentially colocalize I$\sb{\rm K\lbrack Ca\rbrack}$ channels with specific Ca$\sp{2+}$ channel subtypes. The functional colocalization of Ca$\sp{2+}$ and I$\sb{\rm K\lbrack Ca\rbrack}$ channels may be an important regulatory mechanism in both developing and mature vertebrate neurons. / Source: Dissertation Abstracts International, Volume: 55-04, Section: B, page: 1321. / Major Professor: Stuart E. Dryer. / Thesis (Ph.D.)--The Florida State University, 1994.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_77174 |
| Contributors | Wisgirda, Mary E., Florida State University |
| Source Sets | Florida State University |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | 184 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
Page generated in 0.0016 seconds