calcimycin and Brain-Ischemia

The role of SK(Ca) and IK(Ca) channels in myogenic tone and endothelium-derived hyperpolarizing factor (EDHF) responsiveness was investigated under control conditions and after ischemia and reperfusion in parenchymal arterioles (PA) versus middle cerebral arteries (MCA).. MCA and PA were dissected from male Wistar rats that were ischemic for 1 hour with 24 hours of reperfusion (n=12) or sham controls (n=12). Basal tone and reactivity to apamin (300 nmol/L), TRAM-34 (1.0 micromol/L), and nitro-L-arginine (0.1 mmol/L) were compared in PA and MCA pressurized to 40 mm Hg and 75 mm Hg, respectively. SK(Ca) and IK(Ca) channel mRNA expression was measured using real-time PCR.. PA developed greater basal tone than MCA (42+/-4% versus 19+/-3%; P<0.01). Addition of apamin and TRAM-34 increased tone of PA by 25+/-3% and 16+/-2%, respectively, whereas MCA had no response to either inhibitor. After ischemia and reperfusion, the response to nitric oxide synthase inhibition (NOS) was diminished in PA, whereas EDHF responsiveness was preserved. In addition, stimulated EDHF dilation was partially reversed by apamin and completely reversed by TRAM-34 in both control and ischemic PA. SK(Ca) and IK(Ca) channel mRNA expression was similar in PA and MCA and not altered by ischemia and reperfusion. However, IK(Ca) channel mRNA expression was 4- to 5-fold greater than SK(Ca) channels.. It appears that SK(Ca) and IK(Ca) channel activity diminishes basal tone of PA, but not MCA. The preservation of EDHF responsiveness of PA after ischemia and reperfusion suggests an important role for this vasodilator under conditions when NOS is inhibited.

Topics: Animals; Apamin; Arterioles; Biological Factors; Brain Ischemia; Calcimycin; Disease Models, Animal; Enzyme Inhibitors; Intermediate-Conductance Calcium-Activated Potassium Channels; Ionophores; Male; Middle Cerebral Artery; Nitric Oxide; Nitroarginine; Pyrazoles; Rats; Rats, Wistar; Reperfusion Injury; RNA, Messenger; Small-Conductance Calcium-Activated Potassium Channels; Vasodilation

Diffusion magnetic resonance imaging (MRI) provides a surrogate marker of acute brain pathology, yet few studies have resolved the evolution of water diffusion changes during the first 8 hours after acute injury, a critical period for therapeutic intervention. To characterize this early period, this study used a 17.6-T wide-bore magnet to measure multicomponent water diffusion at high b-values (7 to 8,080 s/mm(2)) for rat hippocampal slices at baseline and serially for 8 hours after treatment with the calcium ionophore A23187. The mean fast diffusing water fraction (Ffast) progressively decreased for slices treated with 10-microM/L A23187 (-20.9 +/- 6.3% at 8 hours). Slices treated with 50-micromol/L A23187 had significantly reduced Ffast 80 minutes earlier than slices treated with 10-microM/L A23187 (P < 0.05), but otherwise, the two doses had equivalent effects on the diffusion properties of tissue water. Correlative histologic analysis showed dose-related selective vulnerability of hippocampal pyramidal neurons (CA1 > CA3) to pathologic swelling induced by A23187, confirming that particular intravoxel cell populations may contribute disproportionately to water diffusion changes observed by MRI after acute brain injury. These data suggest diffusion-weighted images at high b-values and the diffusion parameter Ffast may be highly sensitive correlates of cell swelling in nervous issue after acute injury.

Topics: Acute Disease; Animals; Brain Injuries; Brain Ischemia; Calcimycin; Diffusion; Diffusion Magnetic Resonance Imaging; Disease Models, Animal; Edema; Hippocampus; Ionophores; Male; Neurons; Organ Culture Techniques; Rats; Rats, Long-Evans

Pial arterioles have diverse mechanisms for endothelium-dependent dilations. In mice, different mechanisms or endothelium-derived mediators exist for each of the following dilators: acetylcholine, bradykinin, and calcium ionophore A-23187. This study tests the response to each of these dilators during profound ischemia. The response to sodium nitroprusside, an endothelium-independent dilator, was also tested.. In each mouse, ischemia was produced by bilateral carotid artery ligation that reduced cortical blood flow by approximately 90% as determined by laser-Doppler flowmetry. In separate studies of 10 mice each, dilations of pial arterioles to two doses of each dilator were compared before and after 10 minutes of occlusion, with the occlusion continuing during the second set of measurements. The dilator was applied in the suffusate bathing the pial surface exposed at a craniotomy site. Diameters were monitored by in vivo television microscopy and image splitting.. The dose-dependent dilations to acetylcholine, bradykinin, and calcium ionophore A-23187 were each profoundly depressed during ischemia. The response to sodium nitroprusside was not depressed. In all cases, the ischemia was accompanied by arteriolar narrowing of approximately 25% and by obvious slowing of blood flow observed by intravital microscopy. Superoxide dismutase plus catalase failed to prevent the depressed response to acetylcholine.. Endothelium-dependent dilations, mediated by diverse endothelium-derived relaxing factors, are depressed during ischemia of 10 to 15 minutes' duration. This cannot be a nonselective effect on vessel responsivity caused by constriction, reduced flow, or reduced intraluminal pressure during ischemia because under the same conditions dilation to endothelium-independent sodium nitroprusside is preserved. The selective endothelial dysfunction may play a role in exacerbating ischemia by precluding the ability of some dilators, released during ischemia, to dilate the resistance vessels.

Topics: Acetylcholine; Animals; Arterioles; Bradykinin; Brain Ischemia; Calcimycin; Cerebrovascular Circulation; Dose-Response Relationship, Drug; Image Processing, Computer-Assisted; Ionophores; Laser-Doppler Flowmetry; Male; Mice; Mice, Inbred ICR; Microscopy; Nitric Oxide; Nitroprusside; Pia Mater; Television; Vasodilation; Vasodilator Agents

1. The brain cytoprotective effects of a putative calcium-associated protein kinase inhibitor, HA1077, as well as a calcium entry blocker nicardipine were evaluated in models of cerebral ischaemia in Mongolian gerbils. Morphological changes characterizing delayed neuronal death of selectively vulnerable CA1 pyramidal neurones in the hippocampus of the Mongolian gerbil brain occurred 7 days after transient bilateral occlusion of the common carotid arteries. 2. A single injection of HA1077 (1 and 3 mg kg-1, i.p.) 5 min after the occlusion led to a dose-dependent protection of the CA1 neurones. Repeated administrations of HA1077 (1 and 3 mg kg-1, i.p., twice daily for 7 days post-ischaemia) revealed an increase in the number of normal cells, compared to findings with a single administration. 3. In contrast to HA1077, nicardipine (0.3 and 1 mg kg-1, i.p.) did not reduce neuronal degeneration. 4. HA1077 did not interact with the ion channel within which MK-801 binds, as determined by receptor binding. 5. The calcium ionophore, A23187, caused a tonic contraction in canine cerebral arterial strips. HA1077, but not nicardipine, relaxed the A23187-induced contraction, concentration-dependently. 6. These results suggest that blockade of the intracellular actions of calcium may provide protection against ischaemic damage in the brain.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Animals; Brain Ischemia; Calcimycin; Calcium Channel Blockers; Cell Death; Dogs; Gerbillinae; In Vitro Techniques; Isoquinolines; Male; Nicardipine; Rats; Rats, Inbred Strains; Vasoconstriction