BACKGROUND The use of radioactive microspheres (RM) for the measurement of regional myocardial blood flow (RMBF) is limited and inaccessible to many investigators due to radiation safety concerns and radioactive waste disposal problems. Therefore, a new method for the measurement of RMBF using colored microspheres (CM) was developed. METHODS AND RESULTS Polystyrene spheres (diameter, 15 +/- 0.1 [SD] micron; density, 1.09 g/ml) were dyed with one of five colors. With the injection of CM into the left atrium or into a coronary perfusion line, RMBF and its distribution can be determined. CM are extracted from the myocardium and blood by digestion with potassium hydroxide and subsequent microfiltration. The dyes are then recovered from the CM within a defined volume of a solvent, and their concentrations are determined by spectrophotometry. The separation of composite absorbance spectra by spectrophotometry with the CM technique was as good as the separation of energy spectra by a gamma-counter using the RM technique. Leaching of dye from the CM was less than 0.1% during a 2-month period in vitro. Significant leaching of dye from the microspheres also did not occur during 8 hours in the blood and myocardium of four anesthetized dogs in vivo. For further validation of this method, pairs of CM and RM (15.5 +/- 0.1 [SD] microns) were simultaneously injected under five different RMBF conditions (range, 0-10 ml/[min.g]) into the left anterior descending coronary artery of four anesthetized pigs, with coronary inflow as a flow reference, or into the left atrium of four anesthetized dogs using aortic blood withdrawal as a reference. The relation between RMBF determined by CM and RM was CM = 0.01 + 1.00.RM (r = 0.98, n = 1,080 data points) in the pigs, and CM = -0.19 + 0.92.RM (r = 0.97, n = 1,813 data points) in the dogs. CONCLUSIONS Measurement of RMBF with CM yields values very similar to those of RM. Their use is less expensive and avoids all the disadvantages related to radioactivity, thus offering an alternative method for as many as five RMBF measurements in a single experiment.

A close relationship exists between regional myocardial blood flow (RMBF) and function during acute coronary inflow restriction (perfusion-contraction matching). However, the relationship of flow and function during coronary microvascular obstruction is unknown. In 12 anesthetized dogs, the left circumflex coronary artery was perfused from an extracorporeal circuit. After control measurements, 3,000 microspheres (42 micrometer diameter) per milliliter per minute inflow were injected to cause a microembolism (ME, n = 6). With unchanged systemic hemodynamics and RMBF, posterior systolic wall thickening (PWT) decreased from 19.8 +/- 1.9% SD at control to 13.3 +/- 4.0, 10.3 +/- 3.8, and 6.9 +/- 4.7% (P < 0.05 vs. control) at 1, 4, and 8 h, respectively. For comparison, inflow was progressively reduced to match PWT to that of the ME group at 1, 4, and 8 h (stenosis, STE, n = 6). RMBF in the STE group was reduced in proportion to PWT. Infarct size was not different among groups (6.5 +/- 4.5 vs. 3.4 +/- 3.2%). However, the number of leukocytes infiltrating the area at risk was significantly greater in the ME group than in the STE group. Coronary microembolization results in perfusion-contraction mismatch and is associated with an inflammatory response.

During myocardial ischemia, connexin 43 (Cx43) is dephosphorylated in vitro, and the subsequent opening of gap junctions formed by two opposing Cx43 hexamers was suggested to propagate ischemia/reperfusion injury. Reduction of infarct size (IS) by ischemic preconditioning (IP) involves activation of protein kinase C (PKC) and p38 mitogen activated protein kinase (MAPK), both of which can phosphorylate Cx43. We now studied in anesthetized pigs whether IP impacts on Cx43 phosphorylation by measuring the density of non-phosphorylated and total Cx43 (confocal laser) during normoperfusion and 90-min ischemia in non-preconditioned and preconditioned hearts. Co-localization of PKCalpha, p38MAPKalpha, and p38MAPKbeta with Cx43 and the activity of p38MAPK were assessed. IP by 10 min ischemia and 15 min reperfusion reduced IS. Non-phosphorylated Cx43 remained unchanged during ischemia in preconditioned hearts, while it increased from 35+/-3 to 75+/-8 AU (P<0.05) in non-preconditioned hearts. Co-localization of PKCalpha, p38MAPKalpha, and p38MAPKbeta with Cx43 during ischemia increased only in preconditioned hearts. While the ischemia-induced increase in p38MAPKalpha activity was comparable in preconditioned and non-preconditioned hearts, p38MAPKbeta activity was increased only in preconditioned hearts. Blockade of p38MAPK by SB203580 attenuated the IS-reduction and the increased p38MAPK-Cx43 co-localization by IP. We conclude that IP increases co-localization of protein kinases with Cx43 and preserves phosphorylation of Cx43 during ischemia.

Protein kinase C⑀ (PKC⑀) plays a central role in ischemic preconditioning (IP) in mice and rabbits, and activated PKC⑀ colocalizes with and phosphorylates connexin43 (Cx43) in rats and humans. Whether or not Cx43 contributes to the mechanism(s) of IP in vivo is yet unknown. Therefore, wild-type (n ϭ 8) and heterozygous Cx43-deficient mice (n ϭ 8) were subjected to 30 min occlusion and 120 min reperfusion of the left anterior descending coronary artery. IP was induced by one cycle of 5 min occlusion and 10 min reperfusion (n ϭ 8/8 mice) before the sustained occlusion. Infarct size was reduced by IP in wild-type mice [11.3 Ϯ 3.4% vs. 23.7 Ϯ 7.2% of the left ventricle (LV), P Ͻ 0.05] but not in Cx43-deficient mice (26.0 Ϯ 6.0% vs. 25.1 Ϯ 3.8% of LV). Also, three cycles of 5 min occlusion and 10 min reperfusion (n ϭ 5) did not induce protection in Cx43-deficient mice (27.6 Ϯ 5.5 % of LV). Thus Cx43 contributes to the protection of IP in mice in vivo. mouse heart in situ; infarct size; gap junctions ISCHEMIC PRECONDITIONING (IP) by brief episodes of ischemia-reperfusion protects the myocardium from the damage induced by a subsequent more prolonged ischemia. Several triggers and mediators of IP have been identified, whereas the final end effector is still unknown (15). Protein kinase C⑀ (PKC⑀) is an established mediator of IP in mice and rabbits, whereas other PKC isoforms may be more important in other species (15). PKC⑀ is involved in signaling complexes with at least 36 proteins (1, 9, 18), among them connexin43 (Cx43) (10), an integral protein of myocardial gap junctions. Activated PKC⑀ colocalizes with Cx43 and contributes to phosphorylation of Cx43 in rats (3) and humans (2), which might then modulate gap junction transmission characteristics and intercellular communication. Indeed, in isolated mouse hearts, uncoupling of gap junctions using heptanol abolished infarct size reduction by IP (8). The data on the effect of gap junction uncoupling on infarct size per se are controversial. Pretreatment with the gap junction uncoupler heptanol had no effect on infarct size in isolated rabbit hearts (6), but heptanol given during early ischemia decreased infarct size in isolated rabbit hearts (16). Also, in pigs in vivo heptanol given during early reperfusion decreased infarct size (4). Data on the importance of Cx43 for IP in vivo, however, are lacking. We therefore studied whether or not Cx43 is involved in the cardioprotection by IP using heterozygous Cx43-deficient mice. EXPERIMENTAL PROCEDURESThe experimental protocols were approved by the bioethics committee of the district of Dü sseldorf, Germany. Mice were handled according to the guidelines of the American Physiological Society.We used the in situ mouse heart model developed by Guo et al. (5). Briefly, male and female C57BL/6J wild-type and heterozygous Cx43-deficient mice (B6.129-Gja1 tm1Kdr , JAX mice; Bar Harbor, ME) (12) (weight: 30.5 Ϯ 4.5 g, age: 14-20 wk) were anesthetized with pentobarbital sodium (80 mg/kg ip) and atropine sulfate (0.04 mg/kg ip). Ele...

IS reduction by IPc is a graded phenomenon. Whereas bradykinin is essential during preconditioning ischemia of shorter duration, adenosine is more important during preconditioning ischemia of longer duration.