Ryanodine receptor subtypes regulate Ca2+ sparks/spontaneous transient outward currents and myogenic tone of uterine arteries in pregnancy.

AIMS: Our recent study demonstrated that increased Ca2+ sparks and spontaneous transient outward currents (STOCs) played an important role in uterine vascular tone and haemodynamic adaptation to pregnancy. The present study examined the role of ryanodine receptor (RyR) subtypes in regulating Ca2+ sparks/STOCs and myogenic tone in uterine arterial adaptation to pregnancy. METHODS AND RESULTS: Uterine arteries isolated from non-pregnant and near-term pregnant sheep were used in the present study. Pregnancy increased the association of α and ß1 subunits of large-conductance Ca2+-activated K+ (BKCa) channels and enhanced the co-localization of RyR1 and RyR2 with the ß1 subunit in the uterine artery. In contrast, RyR3 was not co-localized with BKCa ß1 subunit. Knockdown of RyR1 or RyR2 in uterine arteries of pregnant sheep downregulated the ß1 but not α subunit of the BKCa channel and decreased the association of α and ß1 subunits. Unlike RyR1 and RyR2, knockdown of RyR3 had no significant effect on either expression or association of BKCa subunits. In addition, knockdown of RyR1 or RyR2 significantly decreased Ca2+ spark frequency, suppressed STOCs frequency and amplitude, and increased pressure-dependent myogenic tone in uterine arteries of pregnant animals. RyR3 knockdown did not affect Ca2+ sparks/STOCs and myogenic tone in the uterine artery. CONCLUSION: Together, the present study demonstrates a novel mechanistic paradigm of RyR subtypes in the regulation of Ca2+ sparks/STOCs and uterine vascular tone, providing new insights into the mechanisms underlying uterine vascular adaptation to pregnancy.

Pregnancy Increases Ca2+ Sparks/Spontaneous Transient Outward Currents and Reduces Uterine Arterial Myogenic Tone.

Spontaneous transient outward currents (STOCs) at physiological membrane potentials of vascular smooth muscle cells fundamentally regulate vascular myogenic tone and blood flow in an organ. We hypothesize that heightened STOCs play a key role in uterine vascular adaptation to pregnancy. Uterine arteries were isolated from nonpregnant and near-term pregnant sheep. Ca2+ sparks were measured by confocal microscopy, and STOCs were determined by electrophysiological recording in smooth muscle cells. Percentage of Ca2+ spark firing myocytes increased dramatically at the resting condition in uterine arterial smooth muscle of pregnant animals, as compared with nonpregnant animals. Pregnancy upregulated the expression of RyRs (ryanodine receptors) and significantly boosted Ca2+ spark frequency. Ex vivo treatment of uterine arteries of nonpregnant sheep with estrogen and progesterone imitated pregnancy-induced RyR upregulation. STOCs occurred at much more negative membrane potentials in uterine arterial myocytes of pregnant animals. STOCs in uterine arterial myocytes were diminished by inhibiting large-conductance Ca2+-activated K+ (BKCa) channels and RyRs, thus functionally linking Ca2+ sparks and BKCa channel activity to STOCs. Pregnancy and steroid hormone treatment significantly increased STOCs frequency and amplitude in uterine arteries. Of importance, inhibition of STOCs with RyR inhibitor ryanodine eliminated pregnancy- and steroid hormone-induced attenuation of uterine arterial myogenic tone. Thus, the present study demonstrates a novel role of Ca2+ sparks and STOCs in the regulation of uterine vascular tone and provides new insights into the mechanisms underlying uterine vascular adaptation to pregnancy.

From skin to spontaneous lysis: A case of spontaneous tumor lysis syndrome in metastatic melanoma.

Tumor lysis syndrome is a life-threatening complication that often occurs after administration of cytotoxic therapy, but rarely occurs spontaneously without chemotherapy. This vignette describes a 59-year-old male with known extensive metastatic melanoma who presented to the hospital with spontaneous tumor lysis syndrome. Most spontaneous tumor lysis cases occur in patients with acute leukemias and aggressive lymphomas; however, this rare case depicts a patient with melanoma developing tumor lysis before the administration of chemotherapy.

B12 deficiency leading to marked poikilocytosis versus true schistocytosis, a pernicious problem.

Severe vitamin B12 deficiency is caused most commonly by autoimmune atrophic gastritis leading to loss of intrinsic factor. Vitamin B12 deficiency leading to megaloblastic anemia and demyelinating central nervous system disease is well known; however, a rare presentation of B12 deficiency described as pseudothrombotic microangiopathy is not well known. This complication presents with signs of mechanical hemolysis, elevated lactate dehydrogenase (LDH), thrombocytopenia, and a low reticulocyte count, which can be incorrectly diagnosed as thrombotic thrombocytopenic purpura and managed incorrectly. Decreased reticulocyte count and an LDH >2500IU/L is more commonly seen in B12 deficiency. However, recognizing the differences in marked poikilocytosis can be challenging, as seen with megaloblastic changes and true schistocytosis. To illustrate the challenge in differentiating between megaloblastic changes and true schistocytosis, we present the case of a 27-year-old woman who presented to her physician for symptomatic anemia and complaints of nausea, vomiting, and loose stool. She had a hemoglobin of 5.1g/dL, platelet count of 39×109/L, LDH of 9915IU/L, haptoglobin below assay limit, and a reticulocyte count of 2.5%. Peripheral smear showed macrocytic anemia, rare hypersegmented neutrophils, and schistocytes. Vitamin B12 level was less than 50pg/mL, methylmalonic acid was 0.33µmol/L, anti-parietal cell antibody was >1:640, and intrinsic factor blocking antibody was positive-confirming the diagnosis of pernicious anemia. While hospitalized, she was treated with vitamin B12 1000µg intramuscular injections daily and thereafter continued with monthly injections, which ultimately resolved her severe macrocytic anemia.