Delayed cerebral ischemia and spreading depolarization in absence of angiographic vasospasm after subarachnoid hemorrhage

It has been hypothesized that vasospasm is the prime mechanism of delayed cerebral ischemia (DCI) after aneurysmal subarachnoid hemorrhage (aSAH). Recently, it was found that clusters of spreading depolarizations (SDs) are associated with DCI. Surgical placement of nicardipine prolonged-release implants (NPRIs) was shown to strongly attenuate vasospasm. In the present study, we tested whether SDs and DCI are abolished when vasospasm is reduced or abolished by NPRIs. After aneurysm clipping, 10 NPRIs were placed next to the proximal intracranial vessels. The SDs were recorded using a subdural electrode strip. Proximal vasospasm was assessed by digital subtraction angiography (DSA). 534 SDs were recorded in 10 of 13 patients (77%). Digital subtraction angiography revealed no vasospasm in 8 of 13 patients (62%) and only mild or moderate vasospasm in the remaining. Five patients developed DCI associated with clusters of SD despite the absence of angiographic vasospasm in three of those patients. The number of SDs correlated significantly with the development of DCI. This may explain why reduction of angiographic vasospasm alone has not been sufficient to improve outcome in some clinical studies.

Combined modulation of the mitochondrial ATP-dependent potassium channel and the permeability transition pore causes prolongation of the biphasic calcium dynamics

The permeability transition pore (PTP) and the ATP-dependent potassium (mtK-ATP) channel of mitochondria are known to play key roles in mitochondrially mediated apoptosis. We investigated how modulation of the permeability transition pore (PTP) and the ATP-dependent potassium (mtK-ATP) channel, either as single elements or in combination, affects the proapoptotic intracellular calcium ([Ca(2+)](i)) transients and the mitochondrial membrane potential (psi(m)). For this purpose a model was established exploring the [Ca(2+)](i) transients in N2A cells using continuous application of ATP that causes a biphasic [Ca(2+)](i) response. This response was sensitive to endoplasmatic reticulum (ER) Ca(2+) depletion and a smooth ER Ca(2+)-ATPase (SERCA) antagonist. PTP inhibition by cyclosporine A (CsA) or its non-immunosuppressive derivative NIM811 caused an amplification of the secondary [Ca(2+)](i) peak and induced a hyperpolarization of psi(m). Both the putative mtK-ATP channel inhibitor 5-hydroxydecanoate (5-HD) and the opener diazoxide ameliorated the ATP-induced secondary [Ca(2+)](i) peak. The effect of diazoxide was accompanied by a depolarization of psi(m) whereas 5-HD had no effect on psi(m). When diazoxide and CsA or NIM811 were applied together the secondary [Ca(2+)](i) rise did not return to baseline and a not significant hyperpolarization of psi(m) was observed. So, simultaneous inhibition of PTP and activation of the mtK-ATP channel prevents the increased slope of the secondary [Ca(2+)](i) peak induced by CsA (or NIM811) and also the depolarization after diazoxide application. Hence, we propose that modulation of one of these channels leads to functional changes of the other channel by means of Delta[Ca(2+)](i) and Deltapsi(m).

Intrinsic optical signal of retinal spreading depression: Second phase depends on energy metabolism and nitric oxide

Spreading depression (SD) is a wave-like phenomenon that spreads through the gray matter of central nervous tissue. The aim of this work is to investigate how cellular energy supply and nitric oxide (NO) influence the recovery period after SD wave propagation. We have examined the SD wave in chicken retina by registration of the intrinsic optical signal (IOS). The changes of the IOS were observed via a microscope, transferred to a photomultiplier and amplified. The IOS of the SD wave consists of two phases. The first phase of IOS coexists with cellular swelling induced by ion distribution; the second phase is thought to reflect metabolic changes and reflects the refractory (recovery) period. To analyze the IOS, the amplitude, the duration and the front and the back maximal slopes of the both phases were analyzed. To reduce the cellular level of ATP the blocker of glucose transport-dexamethasone (glucocorticoid hormone) and the blocker of the respiratory chain-potassium cyanide were used. Sodium nitroprusside and trinitroglycerine were chosen as NO-donors. Our results show that during and after SD wave propagation (i) increased NO concentration changes the first and the second phases of IOS (duration of both phases is NO independent), (ii) reduced glucose uptake leads to an increased second phase duration and (iii) block of the respiratory chain prolongs the first phase. According to the results here presented, we propose that glycogen synthesis is one of the mechanisms reflected by the second phase of the IOS.

The human mitochondrial KATP channel is modulated by calcium and nitric oxide: a patch-clamp approach

ATP-sensitive potassium channels of the inner mitochondrial membrane (mtKATP) are blocked by ATP. They are suggested to be involved in protective mechanisms such as ischemic preconditioning (IPC). Here we identify this channel type for the first time in a human cell line (Jurkat cells). Vesicles of the inner mitochondrial membrane (mitoplasts) were prepared by hypoosmotic shock. Single-channel currents were measured by means of the patch-clamp technique. We identified an outward-rectifying channel with a slope conductance of 15 and 82 pS at negative and positive potentials, respectively. The block by 5-hydroxydecanoic acid and inhibition by ATP characterize this channel as the mtKATP channel. ATP also increased the frequency of events within the burst. This effect was modulated by the Ca2+-bath concentration. We also show that the human mtKATP channel is a direct target for nitric oxide that blocked the channel activity. Although the molecular structure of this channel type is still unknown, its characterization as an outward-rectifying channel and modulation by calcium ions and nitric oxide may help to elucidate its functional significance, which possibly implicates a role in cell survival after IPC.

Extracellular potassium alters frequency and profile of retinal spreading depression waves

The phenomenon of spreading depression (SD) was observed in chicken retina by means of optical registration via a microscope and a CCD camera applying modern methods of image processing for optimized evaluation of the wave profiles. The propagation dynamics of SD waves was investigated as a function of extracellular potassium. Two main findings were obtained. Firstly, the frequency of spontaneous wave generation increased with the increase of K+ concentration. Secondly, there was an effect of potassium on the wave profile. In particular, the recovery zone of SD waves was shortened at increased K+. This effect was not only due to the dispersion relation of waves in excitable media as shown by the result of the mechanically induced wave trains. Applying the basic principles of chemical excitability for the interpretation of the data led us to the conclusion that these potassium effects are due to perturbations of an autocatalytic reaction to be further explored.