Numbers of people do like I was doing: do the experiments - not to publish but to see what is going on. In my experiments, number of which have not been published and will never be published, I concluded that the potassium channels, while important for the basic tone of the smooth muscle (rat tracheal and aorta), probably do not contribute enormously in the regulation of the active tone of the muscle. Indeed, it is valuable to know more about their effects since when seen as contributing to the muscle tone, there may be conditions where they could be of great importance.

Depends on vessel and conditions (constrictor agent dilator agent). I get relaxations that are completely insensitive to BKCa (despite BKCa being expressed and partially active under constrictor tone) and relaxations that do have BKCa component under similar conditions. So I would say if the relaxation is well characterised -(preferably with simultaneous measurement of membrane potential) and constrictor tone is matched to control levels (IbTx often causes constriction or sensitises constrictor agents) then it is fine to make those claims without a cascade assay. However your point highlights that  reliance on a single technique, no matter how well done is not the way to conduct science in the modern world and we must answer problems in more than one way to demonstrate reproducibility and help strengthen the evidence for a given response mechanism.

Yes IbTx can cause pretty big constrictions. In rabbit iliac arteries held at 5 mN pretension IbTx contracts the tissue to a similar level as 1 uM PhE.

As Alister says, it depends on the prep. In pressure myography, if the vessel has myogenic tone then IbTx alone may cause constriction as the myogenic tone results from membrane depolarization and elevated intracellular [Ca2+] in the smooth muscle cells, both of which would be expected to activate BKCa in the muscle. In our experiments this is most clearly seen in cerebral arteries, but IbTx also constricts skeletal muscle arteries. We haven't seen much effect in mesenterics. As far as reflecting 'basal' EDHF activity, I don't think so. I would argue the effects of IbTx alone on smooth muscle tone are due to actions directly on smooth muscle, not EDHF.     

Yes, IbTx will depolarise the cell membrane.

What is EDHF, please? I worked on the EpDRF for some time and it tuned out to be "a concept".

I think EDHF is a concept EDH is more accurate as it describes a set of processes  which evoke  endothelium dependent hyperpolarization and relaxation of smooth muscle. These include factors but also gap juntional communication. I Think most agree the term EDHF is redundant unless referring to a specific factor like an EET and then it is probably  better to just refer to that factor. Indeed by this definition  NO is also and EDHF and I think no one uses the term EDRF anymore and just refer to NO. IF you have relaxation you can't attitude to a  a single factor or is independent  of  a factor  then EDH  is probably  the correct term.

Endothelium derived hyperpolarizing factor. Like NO, it is proposed to be a diffusible relaxing factor, but evokes hyperpolarization and is distinct from NO and prostanoids. In myograph studies, residual relaxations observed in the presence of NOS and COX inhibitors WERE termed EDHF-type. However, EDHF as a generic term is pretty much obsolete now, because it can involve passage of current through gap junctions. Usually it is now referred to endothelium-derived hyperpolarization (EDH). EDHF can only now be used when you have clear evidence demonstrating a transferrable factor. Epoxyeicosatrienoic acids, hydrogen peroxide and K+ ions, among others, have been proposed as EDHFs in specific vessels. However there is massive variability in the nature of EDHF between vessels, species, disease state, development etc. It is a more prominent mechanism of vasodilation in small vessels and the microcirculation, and is sometimes amplified in disease states to compensate for reduced NO.

apologies my last post was written on my phone so auto correct has given some basic errors!

The human coronary microcirculation is a well characterized (and of course clinically relevant) example of a vascular bed that can use EDH to compensate for reduced NO in disease. It also serves as an example of variability in EDH. For example, in arterioles from patients with CAD flow and bradykinin responses are preserved but no longer sensitive to L-NAME. Bradykinin evoked responses mainly work through a transferable, IbTx-insensitive action of Nox2 derived H2O2, which also inhibits epoxygenases..... in the presence of catalase an EET component of relaxation working through BKCa is unmasked. However, for flow induced dilation EETs appear to promote a mechanism of vasodilation through Nox2-mitochondria linked H2O2 which is also dependent on TRPV4. In this case, the H2O2 mediated dilation IS sensitive to IbTx, but the release of EETs (unlike to bradykinin) is not detected. Massive variability in the same vessel - just two modes of endothelial stimulation. My latest review on the coronary circulation covers this in detail. 

......... and that's before we get to vessels working through gap junctions, and some even use a combination of both

The answer is NO

Dear Jai

"The answer is NO" may be interesting as an answer in some "journal of jokes" or as a part of some Zen demonstration. Here we need more.

Jai, would you care to elaborate?

Well lets understand from our basics that BKCa channels are no doubt very sensitive to intrinsic voltage (as rightly pointed out by you), but iberiotoxin does not interfere with this function. The relaxation of Channels are due to several polarisation effect which iberiotoxin does not bring about. There are several papers on the function of iberiotoxins (of course many of these are talking about  many ifs and buits).

Jai, thank you for your answer. I will try to find the papers on iberiotoxin you spoke about. The idea that IbTx does not interfere with channel sensitivity to voltage is new to me so I'll definitely look that one up. Useful to know! Many thanks

The iberiotoxin OF COURSE, by blocking the potassium channel, depolarizes smooth muscle membrane (K accumulates in the cell). Look up Cornfield DN papers on K+ channel and iberiotoxin.

Guys,

I think using «increased voltage”, “intrinsic voltage” and “relaxation of a channel” all do not make much sense in this discussion. Dear Jai, be sincere, you never did those experiment, did you? Therefore, let us go back to some textbooks first, what do you think?

This means that the membrane would hyperpolarize (becomes more negative interior – if K+ channel is activated and opened – with chromakalim, or krimakalim for example) or depolarize (becomes less negative interior – what happens if K+ channel is blocked and K+ accumulates inside the cell). If it would depolarize sufitiently, it may reach threshold of Ca++ channels and Ca++ would rush into the cell, inducing further depolarization and membrane potential may overshoot the resting potential by + 30-50mV, or even generate spikes on the top of that plateau o another 30-50 mV. The rat arteries would then simultaneously go into contraction and remain at some plateau, or quite often they may exhibit slow waves.

Iberiotoxin will certainly produce depolarisation and contraction. All K+ blockers overlap to some extent and some tissues are more or less sensitive to some blockers, mirroring to some extent the specific K+ channles distribution.