Biology question below?

Question

What would most likely happen to an action potential if it encountered a large patch of plasma membrane that was devoid of voltage- gated channels?

Answer 1

depends how large the patch is. The electric potential will be only able to spread electrotonically. That means the signal will be attenuated with distance.
Depending on the distance the voltage difference may be below the threshold for opening the voltage gated channels so it just fizzles out.
Question to you: why do you put a biology question into higher education? Doesn't make sense to me.

Answer 2

A wide variety of ionic currents underlie the excitability and firing patterns of -motoneurones in the mammalian spinal cord (McLarnon, 1995; Kiehn & Eken, 1998; Kiehn et al. 2000; Rekling et al. 2000; Powers & Binder, 2001). Studies of macroscopic (Takahashi, 1990) and single channel (Safronov et al. 1996) membrane currents in -motoneurones have revealed the presence and functional characteristics of multiple types of voltage-gated K+ currents, including outwardly directed transient (A-type; IA) and delayed rectifier (IK) currents. The expression of these currents is developmentally regulated (Gao & Ziskind-Conhaim, 1998; Ribera, 1999), but the precise pattern of expression and localization of the underlying voltage-gated K+ channels in -motoneurones is not known.

Several lines of evidence suggest that channels formed by Kv2.1 subunits (members of the voltage-gated Shab family) are major contributors to delayed rectifier K+ currents in vertebrate neurones (Murakoshi & Trimmer, 1999; Blaine & Ribera, 2001). Kv2.1 subunits may form heteromeric channels in association with modulatory -subunits, or, with other subunits of the Kv2.1 subfamily (e.g. Kerschensteiner et al. 2003). Kv2.1 channel proteins have a unique C-terminal domain proximal restriction and clustering signal and are preferentially targeted to the soma and proximal dendrites of cultured hippocampal neurones and a variety of cortical principal cells and interneurones (Scannevin et al. 1996; Du et al. 1998; Lim et al. 2000; Antonucci et al. 2001). Since Kv2.1 subunits are expressed throughout the CNS, it is of interest to determine whether they exhibit similar polarized expression patterns in the soma and dendrites of spinal motoneurones and interneurones.

Single channel and ensemble IA and IK currents recorded from membrane patches on the soma and apical dendrites of hippocampal and cortical pyramidal neurones revealed key information about the density and distribution of voltage-gated K+ channels in these central neurones (e.g. Hoffman et al. 1997; Bekkers, 2000a,b; Korngreen & Sakman, 2000; see also Storm, 2000). These studies demonstrate gradients of channel density along the dendrites, although there are specific differences in the precise organization of the channels in the two main cell types that were analysed (Storm, 2000). However, even in neurones that are amenable to direct patch recording, questions remain as to whether or not the recorded channels are present in synaptic and/or extrasynaptic membrane in the soma and dendrites.

Faced with the difficulty of obtaining comprehensive patch-clamp data from motoneurone dendrites in situ, channel localization using immunohistochemistry is a valuable step in understanding the role(s) of specific postsynaptic voltage-gated K+ channels in motoneurones, and other spinal neurones. This approach, even though it cannot determine channel function, can provide direct evidence that addresses the critical question of whether or not the channels are present at synaptic or extrasynaptic sites in the postsynaptic membrane. Detailed ultrastructural analyses have previously revealed that approximately 50% of the somatic membrane area (and a slightly lower proportion of dendritic membrane) of -motoneurones is associated with a structurally and functionally diverse set of presynaptic nerve terminals; the remaining, extrasynaptic, surface membrane is largely apposed by glial processes (e.g. Conradi et al. 1979; Kellerth et al. 1979; Rose & Neuber-Hess, 1991; Brännström, 1993; Starr & Wolpaw, 1994; Fyffe, 2001). A specific population of presynaptic terminals, the C-terminals (Conradi, 1969), form synapses exclusively on the soma and proximal dendrites of -motoneurones, and although they are by no means the most numerous class of synapse their large size means that they contribute a significant proportion of the overall synaptic coverage at the soma (e.g. Fyffe, 2001). The synapses established by C-terminals are characterized by the presence of subsynaptic cisternae, and they have been demonstrated to be cholinergic in nature (Nagy et al. 1993; Li et al. 1995; Hellström et al. 1999; Wetts & Vaughn, 2001). In addition, these cholinergic C-terminals are associated with postsynaptic muscarinic m2-type receptors in spinal -motoneurones (Skinner et al. 1999; Hellström et al. 2003).

In the present study, specific antibodies were used to define the membrane distribution of Kv2.1 channel subunits in -motoneurones and interneurones in the rat spinal cord. Channel subunit expression and distribution were cell type specific; moreover, large clusters of Kv2.1 subunit-containing channels in -motoneurones were primarily targeted to synaptic rather than to extrasynaptic membrane sites, and were found to associate particularly with cholinergic C-terminals on the soma and proximal dendrites. Preliminary data from this study have been published in abstracts (Muennich et al. 2002; Fyffe et al. 2002).

Answer 3

what he said ^ ^ ^ ^