Hi Stephen and others interested, Inspired by Stephen's great sleuth work on Bloom/Oxytocin/Sex Differences and the Scholar's Creed of yesterday, I finally got off a message to my neurobio colleague at Uof Mich on the membrane channels. (Stephen had suggested in an off-list communication that a primary reference on the distinctiveness of passive and active-transport membrane channels would be useful.) Richard Norman's response is below. Unfortunately, I don't have ready access to the texts he mentions to dig up primary references. . . will add that to my list for future visits to the medical library. If someone else has ready access, let us know if you turn up the seminal paper/s on this ! Sandra Nagel Randall In a message dated 10/26/99 9:00:56 AM Eastern Daylight Time, [EMAIL PROTECTED] writes: > Subj: Re: "Passive" Na+ channels > Date: 10/26/99 9:00:56 AM Eastern Daylight Time > From: (Richard Norman) > To: [EMAIL PROTECTED] > > >Are the "passive" Na+ and K+ channels (those conveying ions along > >concentration gradients and with electrostatic pressure) the same > structures > >that are involved in Na+/K+ active transport (but under different > conditions) > >or are these channels structurally and functionally distinct. I believe > that > >we have been able to ascertain that indeed these channels are distinct. . . > >but we have not been able to track down the primary references for the > >research that demonstrates this fact. > > > Most definitely, the passive and active channels are extremely different. > Any good molecular cell or neurobiology book will have lots of details. For > example, > Alberts, Bray et al, 1994, Molecular Biology of the Cell, 3rd Ed > Z. Hall, 1992, An Introduction to Molecular Neurobiology > Lodish, Baltimore et al, 1995, Molecular Cell Biology, 3rd Ed. > I am at home now and don't have access to a good bibliography, only > introductory texts, so I can't give you the best and most pertinent primary > sources. However, these books will have them. > > However, this is a topic that is so clear that primary literature is almost > irrelevant. The most important point is that the active transport (or > pumping) of Na and K across the membrane is totally separated from the > "passive" flow of the ions across the membrane -- different mechanisms are > at work and different proteins are responsible. > > For example, the sodium pump includes an ATP-ase -- an ATP binding site that > can split ATP, releasing the energy necessary for the transport. The ion > channels responsible for the resting potential, the action potential, or the > synaptic potentials do not bind ATP, do not split ATP, and do not need > energy. The energy involved in producing these activities is derived from > the stored energy in the concentration gradients across the membrane. The > pump is blocked by ouabain, the ion channels have their own separate > blocking agents. > The voltage gated Na, K, and Ca channels responsible for the action > potential are all rather similar, with four large alpha units that can form > functional channels. These are flanked with smaller subunits (different > types of alpha, beta, gamma, and delta) depending on the channel type. The > pump has an entirely different structure.
>Are the "passive" Na+ and K+ channels (those conveying ions along >concentration gradients and with electrostatic pressure) the same structures >that are involved in Na+/K+ active transport (but under different conditions) >or are these channels structurally and functionally distinct. I believe that >we have been able to ascertain that indeed these channels are distinct. . . >but we have not been able to track down the primary references for the >research that demonstrates this fact. Most definitely, the passive and active channels are extremely different. Any good molecular cell or neurobiology book will have lots of details. For example, Alberts, Bray et al, 1994, Molecular Biology of the Cell, 3rd Ed Z. Hall, 1992, An Introduction to Molecular Neurobiology Lodish, Baltimore et al, 1995, Molecular Cell Biology, 3rd Ed. I am at home now and don't have access to a good bibliography, only introductory texts, so I can't give you the best and most pertinent primary sources. However, these books will have them. However, this is a topic that is so clear that primary literature is almost irrelevant. The most important point is that the active transport (or pumping) of Na and K across the membrane is totally separated from the "passive" flow of the ions across the membrane -- different mechanisms are at work and different proteins are responsible. For example, the sodium pump includes an ATP-ase -- an ATP binding site that can split ATP, releasing the energy necessary for the transport. The ion channels responsible for the resting potential, the action potential, or the synaptic potentials do not bind ATP, do not split ATP, and do not need energy. The energy involved in producing these activities is derived from the stored energy in the concentration gradients across the membrane. The pump is blocked by ouabain, the ion channels have their own separate blocking agents. The voltage gated Na, K, and Ca channels responsible for the action potential are all rather similar, with four large alpha units that can form functional channels. These are flanked with smaller subunits (different types of alpha, beta, gamma, and delta) depending on the channel type. The pump has an entirely different structure.
