Vascular amyloid of unknown origin and senile transthyretin amyloid in the lung and gastrointestinal tract of old age: histological and immunohistochemical studies.

The histological and immunohistochemical characteristics and the incidence of amyloid deposits in the tissues of the lung and gastrointestinal tract were investigated in 64 autopsied individuals who were 80 years and older (age range: 80-92 years; mean: 83.3 years). Immunohistochemical examination was performed with antibodies against amyloid A, transthyretin, immunoglobulin lambda and kappa light chain amyloid fibril proteins, beta2-microglobulin, beta protein, apolipoprotein AI, apolipoprotein AII, atrial natriuretic peptide, apolipoprotein E, and amyloid P component. Transthyretin amyloid fibril protein (ATTR) deposits were observed in five cases (7.8%). Gastrointestinal amyloid deposits of unknown origin were observed in the veins of the gastrointestinal tract in 26 cases (40.6%). This amyloid was regarded as portal amyloid with respect to distribution pattern. Pulmonary vascular amyloid deposits of unknown origin were observed in 12 cases (18.8%). These amyloid deposits were found mainly in medium-sized veins in the lungs and did not react with any antibodies against amyloid fibril proteins except apolipoprotein E and amyloid P component. Eleven of the 26 cases (42.3%) showing portal amyloid also showed pulmonary vascular amyloid of unknown origin. The pulmonary vascular amyloid deposits were similar to the portal amyloid deposits with respect to their morphological features and their relation to elastic fibers in the vessels. Further morphological investigation and biochemical analysis of the pulmonary vascular amyloid and portal amyloid will resolve questions of their origins and relation.

Useful polyclonal antibodies against synthetic peptides corresponding to immunoglobulin light chain constant region for immunohistochemical detection of immunoglobulin light chain amyloidosis.

For the immunohistochemical detection of immunoglobulin (Ig) light chain amyloidosis on formalin-fixed, paraffin-embedded tissue sections, we prepared polyclonal antibodies against synthetic peptides corresponding to positions 118-134 of Ig lambda light chain and positions 116-133 of Ig kappa light chain. Nineteen cases of systemic Ig lambda light chain amyloidosis (Alambda amyloidosis), 10 cases of systemic Ig kappa light chain amyloidosis (Akappa amyloidosis), one case of immunohistochemically unclassified systemic amyloidosis and five cases of localized Alambda amyloidosis were tested with these antibodies. Anti-lambda (118-134) antiserum and the affinity-purified antibody both reacted with 18 of the 19 cases of systemic Alambda amyloidosis and all cases of localized Alambda amyloidosis, although the immunoexpression was somewhat variable in intensity in different areas within the same specimen in both systemic and localized amyloidosis. The signal intensities in plasma cells and serum reacted for anti-lambda (118-134) antiserum were weaker than signals obtained with commercially available anti-Ig lambda light chain antibodies. Anti-kappa (116-133) antiserum and the affinity-purified antibody reacted with nine of the 10 cases of systemic Akappa amyloidosis. We conclude that these antibodies against synthetic peptides corresponding to the Ig light chain constant region are useful for the classification of amyloidosis on formalin-fixed, paraffin-embedded tissue sections.

Dystrophin-deficient myocardium is vulnerable to pressure overload in vivo.

OBJECTIVE: Dystrophin provides mechanical reinforcement to the membranes of myocytes. Dystrophin abnormalities are known to cause cardiomyopathy and skeletal muscle disorders; however, the pathogenesis of these abnormalities remains unclear. Dystrophin-deficient skeletal muscle is vulnerable to stresses such as stretch and hypo-osmotic shock. We investigated whether the myocardium of dystrophin-deficient (mdx) mice shows increased vulnerability to acute pressure overload in vivo. METHODS AND RESULTS: Abdominal aortic banding was performed in 12-week-old mdx and control mice. The aortic pressure was measured by cannulation of the right carotid artery at the time of sacrifice. Systolic pressures in mdx mice at 0, 1, 2, 7 and 14 days after aortic banding were 100 +/- 11, 119 +/- 7, 123 +/- 4, 134 +/- 11 and 130 +/- 10 mmHg, respectively. Microscopic analysis revealed focal lesions in the left ventricular wall in banded mdx mice. These lesions consisted of damaged myocytes and inflammatory cells, and also of fibrosis at a late stage. Similar lesions were not observed in non-banded or banded control mice. The proportion of areas of lesions to total left ventricular area increased over time: 1.0 +/- 0.6% in mdx mice without aortic banding (sham, n = 6), and 1.7+/-1.4% 1 day (n = 6, vs. sham, NS), 2.6 +/- 1.9% 2 days (n = 7, vs. sham, P < 0.05), 6.3+ /- 6.5% 7 days (n = 13, vs. sham, P < 0.05) and 9.9 +/- 8.3% 14 days after aortic banding (n=15, vs. sham, P < 0.01). Furthermore, linear regression analysis revealed a significant correlation between percentage of lesion area and systolic pressure in mdx mice (P < 0.05). CONCLUSION: Dystrophin-deficient myocardium is more vulnerable than normal myocardium to pressure overload in vivo. This result has two clinical implications: (1) the patients with dystrophynopathy, such as the Duchenne and the Becker types of muscular dystrophy and X-linked type of dilated cardiomyopathy, who develop arterial hypertension should be treated aggressively, and (2) they should avoid stresses that elevate blood pressure.

Inhibition of p53 function prevents renin-angiotensin system activation and stretch-mediated myocyte apoptosis.

To determine whether stretch-induced activation of p53 is necessary for the up-regulation of the local renin-angiotensin system and angiotensin II (Ang II)-induced apoptosis, ventricular myocytes were infected with an adenoviral vector carrying mutated p53, Adp53m, before 12 hours of stretch. Noninfected myocytes and myocytes infected with AdLacZ served as controls. Stretching of Adp53m-infected myocytes prevented stimulation of p53 function that conditioned the expression of p53-dependent genes; quantity of angiotensinogen (Aogen), AT(1), and Bax decreased, whereas Bcl-2 increased. Ang II generation was not enhanced by stretch. Conversely, stretch produced opposite changes in noninfected and AdLacZ-infected myocytes: Aogen increased twofold, AT(1) increased 2. 1-fold, Bax increased 2.5-fold, and Ang II increased 2.4-fold. These responses were coupled with 4.5-fold up-regulation of wild-type p53. Stretch elicited comparable adaptations in p53-independent genes, in the presence or absence of mutated p53; renin increased threefold, angiotensin-converting enzyme increased ninefold, and AT(2) increased 1.7-fold. Infection with Adp53m inhibited myocyte apoptosis after stretch. Conversely, stretch increased apoptosis by 6.2-fold in myocytes with elevated endogenous wild-type p53. Thus, a competitor of p53 function interfered with both stretch-induced Ang II formation and apoptosis, indicating that p53 is a major modulator of myocyte renin-angiotensin system and cell survival after mechanical deformation.

Analysis of plasma cell clonality in localized AL amyloidosis.

AL amyloidosis is characterized by fibrillar tissue deposits composed of monoclonal immunoglobulin light chains(IgLs). It has been speculated that clonal expansion of plasma cells may occur locally and produce amyloidogenic IgLs. Both immunohistochemistry and molecular genetics are useful for examining plasma cell clonality from paraffin-embedded tissue sections, which are easy to obtain. We evaluated plasma cell clonality in 16 biopsy cases of localized AL amyloidosis using these two methods. A clonal excess of plasma cells was detected in 6 (37.5%) cases immunohistochemically, in 10 (62.5%) cases molecularly, and in 13 (81.3%) cases by at least one of the two methods. These results support local synthesis of the light chain proteins in localized AL amyloidosis.

Conjunctival AL amyloidosis associated with a low-grade B-cell lymphoma.

A rare case of localized amyloidosis associated with a low-grade B-cell lymphoma involving the conjunctiva is described. Although infiltrating small lymphocytes and plasma cells showed little cytological atypia, molecular genetic examination revealed a prominent B-cell clonal immunoglobulin heavy chain (IgH) gene rearrangement in the tumor tissue. Immunoelectronmicroscopic examination showed immunoglobulin lambda light chain specificity in the amyloid deposit and Russell bodies in the surrounding plasma cells. We concluded that the immunoglobulin lambda light chain, produced by the tumor's differentiated plasma cells, is the precursor protein of the localized amyloidosis found in this case.

Insulin-like growth factor-1 attenuates the detrimental impact of nonocclusive coronary artery constriction on the heart.

Coronary artery narrowing (CAN) induces tissue injury, which may involve myocyte necrosis and apoptosis. Insulin-like growth factor (IGF)-1 may counteract cell death, modifying the detrimental effects of myocardial ischemia. On this basis, CAN was produced in female FVB.Igf+/- mice and nontransgenic littermates, and the animals were euthanized 7 days later. CAN consisted of an 82% reduction in the vessel luminal cross-sectional area in both groups of mice. Severe left ventricular dysfunction was present in CAN nontransgenic and transgenic mice, but heart and left ventricular weights increased more in littermates than in FVB.Igf+/- mice. Similarly, the changes in chamber volume and diastolic wall stress were greater in nontransgenic mice. Subacute tissue injury, represented by foci of replacement fibrosis, was 2.6-fold higher in CAN littermates than in FVB.Igf+/- mice. Ongoing myocyte necrosis was 5-fold greater in nontransgenic mice, whereas apoptosis was low and did not differ in the 2 groups of mice. In CAN nontransgenic mice, myocyte necrosis was 12-fold more frequent than apoptosis but, in CAN transgenic mice, these 2 types of cell death were comparable. alpha-Myosin and beta-myosin isoform mRNAs were affected by CAN, but alpha-myosin mRNA was reduced more in nontransgenic mice. In conclusion, myocyte necrosis and replacement fibrosis are the prevailing forms of myocardial damage induced by CAN. Constitutive overexpression of IGF-1 attenuates myocyte necrosis and tissue injury, having no effect on cell apoptosis. These factors limit ventricular dilation, myocardial loading, cardiac hypertrophy, and alterations in alpha- and beta-myosin isoform expression.

Cell death in acromegalic cardiomyopathy.

BACKGROUND: Prolonged untreated acromegaly leads to a nonspecific myopathy characterized by ventricular dysfunction and failure. However, the mechanisms responsible for the alterations of cardiac pump function remain to be defined. Because cell death is implicated in most cardiac disease processes, the possibility has been raised that myocyte apoptosis may occur in the acromegalic heart, contributing to the deterioration of ventricular hemodynamics. METHODS AND RESULTS: Ten acromegalic patients with diastolic dysfunction and 4 also with systolic dysfunction were subjected to electrocardiography, Holter monitoring, 2-dimensional echocardiography, cardiac catheterization, and biventricular and coronary angiography before surgical removal of a growth hormone-secreting pituitary adenoma. Endomyocardial biopsies were obtained and analyzed quantitatively in terms of tissue scarring and myocyte and nonmyocyte apoptosis. Myocardial samples from papillary muscles of patients who underwent valve replacement for mitral stenosis were used for comparison. The presence of apoptosis in myocytes and interstitial cells was determined by confocal microscopy with the use of 2 histochemical methods, consisting of terminal deoxynucleotidyl transferase (TdT) assay and Taq probe in situ ligation. Acromegaly was characterized by a 495-fold and 305-fold increase in apoptosis of myocytes and nonmyocytes, respectively. The magnitude of myocyte apoptosis correlated with the extent of impairment in ejection fraction and the duration of the disease. A similar correlation was found with the magnitude of collagen accumulation, indicative of previous myocyte necrosis. Myocyte death was independent from the hormonal levels of growth hormone and insulin-like growth factor-1. Apoptosis of interstitial cells did not correlate with ejection fraction. CONCLUSIONS: Myocyte cell death, apoptotic and necrotic in nature, may be critical for the development of ventricular dysfunction and its progression to cardiac failure with acromegaly.

Activation of cyclins and cyclin-dependent kinases, DNA synthesis, and myocyte mitotic division in pacing-induced heart failure in dogs.

The inability of myocytes to reenter the cell cycle in vitro may result from a block in the activation of cyclins and cyclin-dependent kinases (cdk). This inhibition may not occur in vivo because myocyte proliferation is present in the failing heart. Thus, cardiac failure was induced by ventricular pacing in dogs, and changes in the quantity of cyclin D2, cyclin A, cyclin B, cdk2, and cell-division cycle-2 (cdc2) in control and paced myocytes were measured. The kinase activity of these nuclear proteins was also established. Finally, DNA synthesis and mitotic indices in myocytes were evaluated. Cyclin D2 in myocytes increased 7-fold after pacing, and cyclin D2-associated kinase activity increased 3-fold. Similarly, cyclin A quantity and activity increased 4-fold. Comparable changes were observed for cyclin B. cdc2 protein increased 8-fold, and cdk2 and cdc2 activity increased 3-fold and 5-fold, respectively. DNA synthesis was detected in 556 myocyte nuclei/10(6) and 2,467 myocyte nuclei/10(6) in control and paced hearts, respectively. Corresponding mitotic indices were 16/10(6) and 95/106, respectively. In conclusion, myocytes react to cardiac failure by activating cyclins and cdk, which are coupled with cell regeneration and the recovery of muscle mass.

Prolactin-secreting macroadenoma in a prepubertal girl.

Prolactin-secreting adenoma, which usually presents with amenorrhea and galactorrhea syndrome, is quite rarely diagnosed in the prepubertal age group. We reported a rare case of a prepubertal prolactin-secreting adenoma and discuss its clinical, radiological and histological features. An 8-year-old girl presented with headache, progressive visual deterioration and precocious puberty. The serum prolactin level was 57.8 ng/ml. Computerized tomography and magnetic resonance imaging revealed an invasive suprasellar tumor. The tumor was partially resected through an interhemispheric approach in a first operation, and residual tumor was resected through the right pterional approach in a second operation. The histological diagnosis was a prolactin-secreting adenoma with high cellular pleomorphism. The Ki-67 labeling index was 5.7%, indicating aggressive biological behavior. Postoperatively, the patient was prescribed bromocriptine as maintenance therapy, and the serum prolactin level became normalized. There is a tendency for diagnosis of a prepubertal prolactin-secreting adenoma to be delayed because there are no endocrinological manifestations. Therefore, the tumor tends to become larger and invasive. Although it is rarely experienced, a prolactin-secreting adenoma should be considered in the differential diagnosis of a large, invasive parasellar lesion in the prepubertal age group.

Comparative efficacies of a calcium antagonist and an alpha1 blocker in elderly hypertensive patients with stroke.

We compared the effects of nilvadipine, a calcium antagonist, and terazosin. an alpha1 blocker, on the hemodynamics and quality of life (QOL) in 12 elderly hypertensive patients with stroke. Following a washout period of 2 weeks. nilvadipine or terazosin was administered for 2 weeks in a randomized crossover manner. At the end of control and treatment periods, we measured the 24-hour-ambulatory blood pressure (BP) and postural change of BP, and interviewed QOL. Terazosin treatment did not show consistent decrease of casual BP, but was associated with a transient decrease of systolic BP and an increase of pulse rate after standing, and enhanced postprandial decrease in BP. Nilvadipine decreased casual BP in a dose-dependent manner, but showed neither postural nor postprandial change of BP. There was no difference in QOL scores with either treatment. Results suggest that nilvadipine is preferable to terazosin for the treatment of elderly hypertensive patients with stroke.

Downgraded non-Hodgkin's lymphoma in the neck occurring as a secondary malignancy.

While the histologic progression from low-grade non-Hodgkin's lymphoma (NHL) to intermediate- or high-grade NHL has been well documented, a rare phenomenon called downgrading in which the histologic conversion of a low-grade NHL occurs after treatment for intermediate- or high-grade NHL has recently been recognized. We report the clinical, immunologic, and genetic features of a patient with a diffuse NHL (intermediate grade) who initially achieved complete remission by both chemotherapy and radiation therapy and then presented with a follicular NHL (low grade) 14 years later. The immunohistochemical study of the lymphoma cells showed B lymphocytes in biopsied lymph nodes at both the initial and the second diagnosis. However, a polymerase chain reaction (PCR) analysis for the immunoglobulin gene rearrangement indicated that the clone of the initial intermediate-grade NHL showed monoclonal cell population, and was distinct from that of the second downgraded form. Given the PCR results and the clinical features, we suggest that a follicular NHL can occur as a secondary malignancy following combined therapy for a diffuse NHL.

Multihormone-producing islet cell tumor of the pancreas associated with somatostatin-immunoreactive amyloid: immunohistochemical and immunoelectron microscopic studies.

Pancreatic islet cell tumors, especially insulinomas, are often associated with amyloid deposition in the tumor tissue. Biochemical analysis has demonstrated that the amyloid protein from insulinoma is derived from islet amyloid polypeptide (or amylin) that is produced by tumor cells originating from beta cells of the islet of Langerhans. We examined a case of malignant pancreatic islet cell tumor with amyloid deposition in the tumor tissue using immunohistochemistry and double-labeling immunogold electron microscopy. The tumors were composed of cells producing multiple hormones, including somatostatin, gastrin, amylin, insulin, calcitonin gene-related polypeptide, and calcitonin. Amyloid deposits reacted with antisomatostatin antiserum but not with other antisera, including antiamylin. The present study demonstrated for the first time that amyloid associated with islet cell tumors is not always derived from amylin and can come from somatostatin.

Stretch-activated channels in arterial smooth muscle of genetic hypertensive rats.

Electrical and contractile responses of small arteries to mechanical stress are reportedly enhanced in spontaneously hypertensive rats (SHR), compared with those in Wistar Kyoto rats (WKY). We have previously shown that stretch-activated cation channels exist in arterial smooth muscle membrane, of which opening causes Na+ and Ca2+ influx and membrane depolarization. We thus hypothesize that activation of stretch-activated channels is enhanced in arterial smooth muscle of SHR compared with WKY. To test this hypothesis, stretch-activated currents were recorded in single smooth muscle cells of resistance mesenteric arteries from SHR and WKY (16 to 24 weeks of age). In the whole-cell recording, membrane stretch was applied by inflating the cell with positive pressure to the recording pipette. Cell-inflation evoked Gd3+-sensitive cation currents. This current appeared with less stretch stimulation and its amplitude was larger in SHR cells compared with WKY cells. In the cell-attached recording, suction to the recording pipette evoked single stretch-activated channel currents (conductance of 32 pS with 150 mmol/L Na+), which were blocked by Gd3+. Channels were activated with less negative pressure and their availability was greater in SHR cells than in WKY cells. Results suggest that the activation of stretch-activated channels is enhanced in smooth muscle of resistance arteries from SHR compared with WKY, which may contribute to the enhanced vascular responses to mechanical stress in SHR.

Effects of CP-060S on membrane channels in vascular smooth muscle cells from guinea pig.

The newly developed cardioprotective drug, CP-060S, (-)-(S)-2-[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]-3-[3-[N-methyl-N- [2-(3,4-methylenedioxyphenoxy) ethyl] amino] propyl]-1,3-thiazolidin-4-one hydrogen fumarate, is reported to possess a vasodilating action. Our objective was to examine the effects of CP-060S on the membrane channels in mesenteric arterial cells from guinea pigs, using whole-cell patch-clamp techniques. CP-060S inhibited the Ca2+ channel current in a concentration-dependent manner (ED50 = 1.7 microM at a holding potential of -80 mV and a stimulation frequency of 0.1 Hz). The inhibition was potentiated by a more depolarized holding potential and a higher stimulation frequency. These effects of CP-060S resembled those of diltiazem and gallopamil more than to those of nifedipine; the inhibition was more frequency dependent and less holding-potential dependent than with nifedipine. Higher concentrations of CP-060S also inhibited the delayed K+ channel currents (ED50 = 18 microM). The present observations suggest that CP-060S exhibits the profile of a Ca2+ channel antagonist, similar to that of diltiazem and gallopamil.

Stretch-activated whole-cell currents in smooth muscle cells from mesenteric resistance artery of guinea-pig.

1. Stretch-activated (SA) channels were studied in smooth muscle cells isolated from mesenteric resistance arteries using the whole-cell patch-clamp method. Membrane stretch was achieved by cell inflation after application of positive pressure through a patch electrode. 2. In the voltage-clamp configuration, cell inflation increased and cell deflation decreased the membrane conductance. Conductance of the evoked current depended on the increase in cross-sectional area of the cell. The current-voltage relationship was linear between -80 and 0 mV, while further hyperpolarization showed a slight inward rectification. 3. The reversal potential of the SA current depended on the extracellular Na+ concentration, suggesting that the inward SA current was carried predominantly by Na+. The SA current was also carried by other cations, suggesting that the channel responsible for this current is a non-selective cation channel. The permeability sequence of cations as assessed by reversal potential was as follows: K+ > or = CS+ > or = Na+ > Li+. The channel was also permeable to Ca2+. 4. Extracellular Ca2+ and Gd3+ inhibited the SA current carried by monovalent cations in a concentration-dependent manner with IC50 (concentration giving 50% of maximal inhibition) values of 0.9 mM and 14 microM, respectively. 5. In the current-clamp configuration, membrane stretch depolarized the cell, and 100 microM Gd3+ inhibited the stretch-induced depolarization. 6. The results suggest that SA cation channels exist in arterial smooth muscle cells. Activation of the channels may modify membrane potential and intracellular ionic environment, and promote stretch-mediated cell responses.

Aortoiliac occlusion associated with the lupus anticoagulant. Report of two cases.

Aortoiliac occlusion due to atherosclerosis is known to occur in elderly people. Two unique cases are documented here in which aortoiliac occlusion was observed in young men. These patients had no identifiable risk factors for developing atherosclerotic thrombosis except for the lupus anticoagulant, an immunoglobulin associated with thromboembolic episodes. Although previously the lupus anticoagulant has been reported to cause thrombosis only in relatively small-sized arteries or veins, it may also be associated with aortoiliac atheromatous occlusion in young men.

Abnormal immunostaining for dystrophin in isoproterenol-induced acute myocardial injury in rats: evidence for change in dystrophin in the absence of genetic defect.

Abnormalities in the gene for Duchenne muscular dystrophy produce skeletal and myocardial changes, by impairing dystrophin production in patients with Duchenne and Becker muscular dystrophy. However, it is not known whether myocardial dystrophin may be altered in patients with other heart diseases. To investigate whether changes in myocardial dystrophin may be induced by acute myocardial injury, the immunostaining patterns of myocardial dystrophin were examined, together with those of myocardial actin, in rats with isoproterenol-induced myocardial damage. Hearts were excised at 6, 12, 24 and 48 h, and 1 and 4 weeks after the subcutaneous administration of 100 mg/kg of isoproterenol. Frozen serial sections were prepared for haematoxylin and eosin staining, and for immunostaining for dystrophin and actin. The immunostaining patterns of actin were used as an indicator of cell injury. The myocardial cells observed were classified into four types, according to staining pattern: normal for both actin and dystrophin (Type 1): normal for actin, but abnormal for dystrophin (Type 2); abnormal for actin, but normal for dystrophin (Type 3); and abnormal for both actin and dsytrophin (Type 4). The percentage of myocardial cells with abnormal staining (Types 2, 3 and 4) at 6, 12, 24 and 48 h after isoproterenol injection was 22.4, 12.6, 16.0 and 2.4%, respectively; most cells were Types 3 and 4. One week after injection or later, no Type 3 or 4 cells were detected, while the percentages of Type 2 cells were 2.7% for 1 week and 2.2% for 4 weeks, significantly higher than the corresponding value in the control group. In conclusion, changes in myocardial dystrophin may occur in isoproterenol-induced myocardial injury in rats.

Immunofluorescence analysis of trihexosylceramide accumulated in the hearts of variant hemizygotes and heterozygotes with Fabry disease.

An immunofluorescence method was applied to detect trihexosylceramide accumulated in the cardiac tissues from a variant hemizygote and a heterozygous female with Fabry disease, the incidence of which had been suspected to be high.

Impaired action of levcromakalim on ATP-sensitive K+ channels in mesenteric artery cells from spontaneously hypertensive rats.

The purpose of the present study was to test the hypothesis that properties of ATP-sensitive K+ channels are altered in arterial smooth muscle cells of hypertensive rats. Using a patch-clamp technique, we compared effects of a K+ channel opener, levromakalim, on membrane currents in mesenteric artery cells from adult Wistar Kyoto rats (WKY) and age-matched spontaneously hypertensive rats (SHR) treated or not treated with hydralazine. Blood pressure was significantly higher in SHR than in WKY or hydralazine-treated SHR. Levcromakalim evoked a time-independent and voltage-insensitive current in a dose-dependent manner in the whole-cell clamp configuration. The reversal potential of the evoked current depended on extracellular K+ concentration. Application of 3 micromol/L glibenclamide, a specific blocker of ATP-sensitive K+ channels, abolished the levcromakalim-evoked current; however, the current was unaffected by either 1 mmol/L tetraethylammonium or 0.3 micromol/L charybdotoxin. These results suggest that the levcromakalim-evoked current was carried through ATP-sensitive K+ channels. In SHR cells, the maximal slope conductance of the levcromakalim-evoked current, normalized by cell capacitance, was decreased, and the dose-response curve was shifted to the right compared with WKY cells. The levcromakalim action was not impaired in cells from hydralazine-treated SHR. In conclusion, the action of levcromakalim on ATP-sensitive K+ channels in SHR mesenteric artery muscle cells was impaired compared with WKY cells. This impairment was corrected by long-term antihypertensive treatment.